Friday, December 18, 2009
DIGITAL COMMUNICATIONS TOTAL NOTES FROM IIT( K)
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Tuesday, December 8, 2009
current affairs part2
) Who is the author of the book ” Sahibs Who Loved India” ?
a) Jagdish
b) Khushwant Singh
c) Chetan Bhagat
d) Nadeem Aslam
2) Who received the Indira Gandhi Prize for Peace, Disarmament and Development ?
a) Mohamed ElBradei
b) Wen Jiabo
c) Taro Aso
d) Nicholas Sarkhosay
3) Which country will be setting up a world Biggest Telescope ?
a) Japan
b) France
c) China
d) India
4) At which place was G-20 Summit held?
a) Washington
b) New York
c) Chicago
d) Los Angeles
5) ” Lisbon Treaty ” is the treaty accepted / adopted by the members of which of the following organizations recently?
a) NATO
b) SAARC
c) European Union
d) NSG
6) Beri-Beri is the deficiency disease caused by the vitamin
a) B1
b) B5
c) A
d) C
7) Who has been appointed as President of Zambia?
a) Dawada Kairaba
b) Isatov Njle
c) Levy
d) Rupia Banda
8) Who is the Pepsico Chief ?
a) Indira Nooyi
b) Indira Mukerjee
c) Kiran Mazumdar
d) Deepa Mirza
9) “Fehmida Mizza” is a woman speaker of National Assembly of
a) Indonesia
b) Iran
c) Pakistan
d) Afghanistan
10) Who is called the “Grand Old Man Of India”?
a) Mahatma Gandhi
b) Dadabhai Naoroji
c) Gokhale
d) Tilak
11) Cabinet Mission came to India in which year?
a) 1942
b) 1932
c) 1916
d) 1946
12) Which five year plan has the objective ” Garibi Hatao” ?
a) first
b) fifth
c) seventh
d) eigth
13) Which river is declared as ” national river” ?
a) Ganga
b) Yamuna
c) Cauveri
d) Krishna
14) “No country for old men” is a
a) book
b) film
c) Drama
d) Poem
15) Hathigumbha inscription belongs to
a)Ashoka
b)Kharavela
c)Harsha
d)Sasaka
a) Jagdish
b) Khushwant Singh
c) Chetan Bhagat
d) Nadeem Aslam
2) Who received the Indira Gandhi Prize for Peace, Disarmament and Development ?
a) Mohamed ElBradei
b) Wen Jiabo
c) Taro Aso
d) Nicholas Sarkhosay
3) Which country will be setting up a world Biggest Telescope ?
a) Japan
b) France
c) China
d) India
4) At which place was G-20 Summit held?
a) Washington
b) New York
c) Chicago
d) Los Angeles
5) ” Lisbon Treaty ” is the treaty accepted / adopted by the members of which of the following organizations recently?
a) NATO
b) SAARC
c) European Union
d) NSG
6) Beri-Beri is the deficiency disease caused by the vitamin
a) B1
b) B5
c) A
d) C
7) Who has been appointed as President of Zambia?
a) Dawada Kairaba
b) Isatov Njle
c) Levy
d) Rupia Banda
8) Who is the Pepsico Chief ?
a) Indira Nooyi
b) Indira Mukerjee
c) Kiran Mazumdar
d) Deepa Mirza
9) “Fehmida Mizza” is a woman speaker of National Assembly of
a) Indonesia
b) Iran
c) Pakistan
d) Afghanistan
10) Who is called the “Grand Old Man Of India”?
a) Mahatma Gandhi
b) Dadabhai Naoroji
c) Gokhale
d) Tilak
11) Cabinet Mission came to India in which year?
a) 1942
b) 1932
c) 1916
d) 1946
12) Which five year plan has the objective ” Garibi Hatao” ?
a) first
b) fifth
c) seventh
d) eigth
13) Which river is declared as ” national river” ?
a) Ganga
b) Yamuna
c) Cauveri
d) Krishna
14) “No country for old men” is a
a) book
b) film
c) Drama
d) Poem
15) Hathigumbha inscription belongs to
a)Ashoka
b)Kharavela
c)Harsha
d)Sasaka
POWER SYSTEM ANALYSIS
1. What are the main divisions of power system?
The generating system,transmission system,and distribution system
2. What are the adv. Of interconnected power system?
1.less no. of generators are required as areserve for operation at peak loads.Hence the
reserve capacity of the generating station gets reduced.
2.less no. of generators which are running without load are required for meeting the sudden
unexpected increase in load.
3. it allows the use of most economical sources of power depending on time.
3.What are the problems of interconnection?
1.it increase the amount of current which flows when a short circuit occurs on a system and
thereby requires the installation of breakers which are able to interrupt a larger current‘
2. synchronism must be maintained between of all the interconnected systems .
4.Define one line diagram.
A simplified diagram by omiting the completed circuit through the neutral and by indicating
the components of the power system by standard symbols rather than by their equivalent circuits.
5.What is meant by impedance diagram.
The equivalent circuit of all the components of the power system are drawn and they are
interconnected is called impedance diagram.
6.What is meant by reactance diagram.
Omitting all static loads ,all resistance. The magnetizing components of each transformer and
the capacitance of the transmission line are reduced from the impedance diagram is called
reactance diagram.
7.Define per unit value.
Per unit of any quantity is defined as the ratio of the quantity ti its base value is expressed as a
decimal.
8. Need for per unit value
the per unit impedance referred to either side of a single phase transformer is the same.
The chance of confussion b/n line and phase quantities in a three phase balanced system is
greatly reduced.
The manufacturers usually produce the impedance values in per unit.
9.Define base current.
Ratio of base MVA to base KV
10.What is the need for short circuit study.
To determine the current interrupting capacity of the circuit breakers so that the faulted
equipments can be isolated.To establish the relay requirements and settings to detect the fault and cause the circuit breaker
to operate when the current flowing through it exceeds the max. value.
11. Define stability study.
Stability studies are performed in order to ensure that the system remains stable
following a severe fault or disturbance.
12. What are the eliments of y bus matrix.
short circuit driving point adm. Short circuit transfer admittance.
13. What are the eliments if Z bus matrix.
Open circuit driving point impedance, open circuit transfer impedances.
14.What are the methods to determine the Ybus$Z bus matrices.
Primitive n/w, n/w grafh theory , incidence matrix
15.What is primitive n/w
Primitive network is a set of unconnected elements which provides information
regardin.
Primitive n/w is a set of unconnected eliments which provides information
regaurding the characteristics of individual eliments only.
16.what is meant gy grafh of a n.w.
Agrafh shows the geometrical interconnection of the elements of a n/w.
17. Define sub graph?
Asub graph is any subset of elements of a graph.
18 What is meant by path of a n/w?
Apath is a subgraph of connected elements with not more than two elements
connected to any one nide.
19.What is meant by connected oriented graph?
Agraph is connected if and only if there is a path b/n every pairs of nodes.If each
element of the connected graph is assigned a direction it is called oriented graph.
20.What are the properties of a graph.
Tree is a sub graph connecting all the nodes of the oriented graph.
Tree is a connected subgraph.
21.Define basic cutest?
Acutset is the minimum set of elements in the graph, which when removed, divide a
connected graph inti two connected subgraph.
.
22. What are the quantities whose base values are required to represent the power system
by reactance diagram.
The base values of voltage, current, pwer and impedance are required to represent the
power system by reactance diagram. Selection of base valuesfor any two of them
determines the base values of the remaining two.
23.What is the need for base values?
The components of power system may operate at different voltage and power levels. It
will be convenient for analysis of power system if the voltage, power, current ratings of
the components of the power system is expressed with referance to a common value
called base value.
24.What is impedance and reactance diagram?
The impedance diagram is the equivalent circuit of power system in which the various
components of power system are represented by their approximate equivalent circuits.
The impedance diagram is used for load flow studies.
The reactance diagram is the simplified equivalent circuit of the power system in which
the various components are represented by their reactance. The reactance ddiagram can
be obtained from impedance diagram if all the resistive components are neglected.
25. What are the approximations made in impedance diagram?
The neutral reactances are neglected.
The shunt branches in equivalent circuit of induction motor are neglected.
26. What are the approximations made in reactance diagram?
The neutral reactances are neglected.
The resistances are neglected.
All static loads and induction motors are neglected.
27. What is a bus?
The meeting point of various components in a power system is called a bus. The bus
is a conductor made of copper having negligible resistance. The buses are considered as a
points of constant voltage in a system.
28. What is bus admittance matrix?
The matrix consisting of the self and mutual admittances of the network of a power
system is called bus admittance matrix.
29. Name the diagonal and off diagonal elements of bus admittance matrix.
The diagonal elements of bus admittance matrix are called self admittances of the
buses and off diagonal elements are called mutual admittances of the buses.
30. What is bus imbedance matrix?
The matrix consisting of driving point impedances and transfer impedances of the
network of a power system is called bus impedance matrix.
31. Name the diagonal elements and off diagonal elements of bus impedance matrix.
The diagonal elements of bus impedance matrix are called driving point impedances
of the buses and off diagonal elements of bus impedance matrix are called transfer
impedances of the buses.
32.What are the methods available for forming bus impedance matrix.
1. Form the bus impedance matrix and then take its inverse to get bus impedance
matrix.
2. Directly form the bus impedance matrix from the reactance diagram. This
method utilizes the techniques of modifications of existing bus impedance
matrix due to addition of new bus.
32. Write the four ways of adding an impedance to an existing system so as to modify
bus impedance matrix.
1. Adding a branch of impedanceZb from a new bus p to the referance bus.
2. Adding a branch of impedance Zb from a new busp to an existing bus.
3. Adding a branch of impedance Zb from an existing busq to the referance
bus.
4. Adding a branch of impedance Zb between two existing buses h and q.
33.What are symmetrical components?
An unbalanced system of N related vectors can be resolved into N systems of
balanced vectors. The N sets of balanced vectors are called symmetrical
components.
33. Write the symmetrical components of three phase system.
1.positive sequence components
3. negative sequence components.
4. zero sequence components.
34. What are positive sequence components?
The positive sequence components of a three phase unbalanced vectors consists of three
vectors of equal magnatude, displased from each other by 120 in phase and having the
same phase sequence as the original vectors.
35. What are negative sequence components?
The negative sequence components of a three phase unbalanced vectors consists of three
vectors of equal magnitude displaced from each other by 120 degree in phase and having
the phase sequence opposite to that of the original vectors.
36.What are zero sequence components?
The zero sequence components of a three phase unbalanced vectors consists of 3 vectors
of equal magnitude and with zero phase displacement from each other.
36. What are sequence impedance and sequence networks?
The sequence impedances are the impedances offered by the devices for the like
sequrnce component of the current.The single phase equivalent circuit of a power system consists of impedances to current f any one sequence is called sequence network.
37.What is meant by positive, negative and zero sequence impedance.
The impedance of the circuit element for positive, negative and zero sequence
component currents are called positive, negative and zero sequence impedances resp.
38.What is meant by positive, negative and zero sequence reactance.
The reactance diagram of a power system, when formed using positive, negative and
zero sequence reactances are called positive, negative and zero sequence reactance
diagram resp.
39.What is load flow or power flow study?
The study of various methods of solution to power system network is reffered to as load
flow study. The solution provides the voltages at various buses, power flowing in various
lines and line losses.
40.What are the information that are obtained from a load flow study.
The information obtained from a load flow study are magnatude and phase of bus
voltages,real and reactive power flowing in each line and the line losses. T he load flow
solution also gives the initial conditions of the system when the transient behaviour of
the system to be studied.
41.What is the need for load flow study.
The load flow study of a power system is essential to decide the best operation existing
system and for planning the future expansion of the system. It is also essential for
designing the power system.
42. What are the quantities associated with each bus ina system?
Each bus in a power system is associated with four quantities and they are real power,
reactive power, magnitude of voltage, and phase angle of voltage.
43. What are the different types of buses.
Load bus,generator bus,slack bus.
44.Define voltage controlled bus?
A bus is called voltage controlled bus if the magnitude of volte\age and real power are
specified for it. In a voltage controlled bus the magnitude of the voltage is not allowed to
change.
45. What is PQ bus?
A bus is called PQ bus when real and reactive components of power are specified for the
bus. In a load bus the voltage is allowed to vary within permissible limits.
46. What is swing bus?
Abus is called swing bus when the magnitude and phase of the bus voltage are specified
for it. The swing bus is the referance bus for load flow solution and it is required for
accounting line losses. Usually one of the generator bus is selected as swing bus.
47.What is the need for slack bus?
The slack bus is needed to account for transmission line losses. In a power system the
total power generated will be equal to sum of power consumed by loads and losses. In a
power system only the generated power and load power are specified for buses. The
slack bus is assumed to generate the power required for losses. Since the losses are
unknown the real and reactive power are not specified for slack bus.
48.What are the operating constraints imposed in the load flow studies?
The operating constraints imposed in load flow studies are reactive power limits for
generator buses and allowable change in magnitude of voltagefor load buses
.
49What are the iterative methods mainly used for solution of load flow study.
The Guass sedal method and Newton Raphson method are the two iterative methods.
50.Discuss the effect of acceleration factor in load flow study.
The acceleration factor is a real quantity and it modify the magnitude of voltage alone.
51What is meant by flat voltage start.
In iterative methods of load flow solution, the initial voltages of all buses exept slack bus
are assumed as 1+j0 pu.This is reffered as flat voltage profile.
52.When the generator buses are treated as load bus.
If the reactive power constraints of a generator bus violates the specified limits then the
generator is treated as load bus.
53. What will be the reactive power and bus voltage whan the generator bus is treated as
load bus.When the generator bus is treated as load bus, the reactive power of the bus is equated to
the limit it has violated, and the previous iteration value of bus voltage is used for
calculating current iteration value.
54. What are the advantages of Guass sedal methoa?
Calculations are simple and so the programming task is lesses.
The memory requirement is less
Useful for small systems
55 What are the disadvantages of Guass seidal method?
Requires large no. of iterations to reach converge
Not suitable for large systems
Convergence time increases with size of the system
56. How approximations is performed in Newton Raphson method?
In N-R method, the set of nonlinear simultaneous equations are approximated to a set of
linear simultaneous equations using tailors series expansion and the terms are limited to
first order approximation.
57.What is Jacobian matrix? How the elements of Jacobian matrix are computed.
The matrix formed from the first derivatives of load flow equations is called Jacobian
matrix.The elements of Jacobian matrix will change in every itration. In each iteration the
elements of the jacobian matrix are obtained by partially differentiating the load flow
equations w.r. t a unknown variable and then evaluating the first derivatives using the
solution of previous iteration
58.What are the adv. Of N-R method?
The N-R method is faster, more reliable and the results are accurate.
Requires less no. of iterations
Suitable for large size system
59. What are the disadv. Of N-R method?
The programming is more complex
The memory requirement is more
60 What is off nominal turns ratio?
When the voltage or turns ratio of a transformer is not used to decide the ratio of base
KV then its voltage ratio is called off nominal turns ratio. Usually the voltage ratio of
regulating transformer will be off nominal ratios
.
61 What is meant by a fault?
A fault in a circuit is any failure which interferes with the normal flow of current. The
faults are associated with abnormal change in current, voltage and frequency of the
power systwm. The faults may cause dan\mage to the equipments if it is allowed to persit
for a long time. Hence every part of the system has been protected by means of relays
and circuir breakers to sence the faults to isolate the faulty part from the healthy part in
the event of fault.
62Why fault accurs in a power system?
The fault occur in a power system due to insulation failure of equipments, flashover of
lines initiated by a lightning stroke, due to permanent damage to conductors and towers
63. How are faults are classified?
The faults are classified as shunt and series faults. The shunt faults are due to short
circuits in conductors and the series faults are due to oped conductors.
64.List the various types of series and shunt fault?
Shunt faults are,
Line to ground fault line to line fault, double line to ground fault, three phase fault.
Series faults are,
One open conductor fault
Two open conductor fault
64 What is symmetrical and unsymmetrical fault?
The fault is called symmetrical fault if the fault current is equal in all the phases. The
fault is called unsymmetrical fault if the fault current is not equal in all the phases.
65. Name any two methods of reducing short circuit current/
By providing neutral reactance.
By introducing a large value of shunt reactance between buses.
66. What is meant by fault calculations/
The fault condition of a power system can be dived into subtransient, transient and steady
state periods. The currents in the various parts of the system and in the fault are different
in these periods. The estimation of these currents for various types of faults at various
locations in the system are commenly reffered as fault calculations.
67.Define stability?
The stability of a system is defined as the ability of power system to return to stable
operation when it is subjected to a disturbance.
68. Define steady state stability
The stady statenstability is defined as the ability of a system to remain stable for small
disturbance.
69. Define transient stability?
The transient stabilitymis defined as the abilitymof a system to remain stable for large
disturbance.
70What is steady state state stability limit?
The steady state stability limit is the max. power that can be transferred by a machine toa
receving system without loss of synchronism.71 Define swing curve? What is the use of
swing curve.The swing curve is the plot between the power angle and time. It is usually plotted for a
transient state to stydy the nature of variation in angle for a sudden large disturbance.
71.Define power angle/
The power angle is defined as the angular displacement of the rotor from synchronously
rotating referance frame.
72Define critical clearing time and critiacal clearing angle
The critical clearing angle is the max. allowable change in the power angle before
clearing the fault, without loss of synchronism.
The critical clearing time can be defined as thw max. time delay that can be allowed to
clear a fault without loss of synchronism.
73.Define equal area criterion?
The equal area criterion for stability states that the system is stable if the area under pvs
angle curve reduces to zero at some value of angle.
74.What is transient state stability limit?
The transient state stability limit is the max. power that can be transmitted by a machine
to a receiving system without loss of synchronism.In steady state the power transferred
by synchronous machine is always less than the steady state stability limit.
75.what is transient stability limit ?
The transient stability limit is the max power that can be transmitted by a machine to a
fault or a receiving system during a transient state without loss of synchronism.The
transient stability limit is always less than the steady state stability limit.
The generating system,transmission system,and distribution system
2. What are the adv. Of interconnected power system?
1.less no. of generators are required as areserve for operation at peak loads.Hence the
reserve capacity of the generating station gets reduced.
2.less no. of generators which are running without load are required for meeting the sudden
unexpected increase in load.
3. it allows the use of most economical sources of power depending on time.
3.What are the problems of interconnection?
1.it increase the amount of current which flows when a short circuit occurs on a system and
thereby requires the installation of breakers which are able to interrupt a larger current‘
2. synchronism must be maintained between of all the interconnected systems .
4.Define one line diagram.
A simplified diagram by omiting the completed circuit through the neutral and by indicating
the components of the power system by standard symbols rather than by their equivalent circuits.
5.What is meant by impedance diagram.
The equivalent circuit of all the components of the power system are drawn and they are
interconnected is called impedance diagram.
6.What is meant by reactance diagram.
Omitting all static loads ,all resistance. The magnetizing components of each transformer and
the capacitance of the transmission line are reduced from the impedance diagram is called
reactance diagram.
7.Define per unit value.
Per unit of any quantity is defined as the ratio of the quantity ti its base value is expressed as a
decimal.
8. Need for per unit value
the per unit impedance referred to either side of a single phase transformer is the same.
The chance of confussion b/n line and phase quantities in a three phase balanced system is
greatly reduced.
The manufacturers usually produce the impedance values in per unit.
9.Define base current.
Ratio of base MVA to base KV
10.What is the need for short circuit study.
To determine the current interrupting capacity of the circuit breakers so that the faulted
equipments can be isolated.To establish the relay requirements and settings to detect the fault and cause the circuit breaker
to operate when the current flowing through it exceeds the max. value.
11. Define stability study.
Stability studies are performed in order to ensure that the system remains stable
following a severe fault or disturbance.
12. What are the eliments of y bus matrix.
short circuit driving point adm. Short circuit transfer admittance.
13. What are the eliments if Z bus matrix.
Open circuit driving point impedance, open circuit transfer impedances.
14.What are the methods to determine the Ybus$Z bus matrices.
Primitive n/w, n/w grafh theory , incidence matrix
15.What is primitive n/w
Primitive network is a set of unconnected elements which provides information
regardin.
Primitive n/w is a set of unconnected eliments which provides information
regaurding the characteristics of individual eliments only.
16.what is meant gy grafh of a n.w.
Agrafh shows the geometrical interconnection of the elements of a n/w.
17. Define sub graph?
Asub graph is any subset of elements of a graph.
18 What is meant by path of a n/w?
Apath is a subgraph of connected elements with not more than two elements
connected to any one nide.
19.What is meant by connected oriented graph?
Agraph is connected if and only if there is a path b/n every pairs of nodes.If each
element of the connected graph is assigned a direction it is called oriented graph.
20.What are the properties of a graph.
Tree is a sub graph connecting all the nodes of the oriented graph.
Tree is a connected subgraph.
21.Define basic cutest?
Acutset is the minimum set of elements in the graph, which when removed, divide a
connected graph inti two connected subgraph.
.
22. What are the quantities whose base values are required to represent the power system
by reactance diagram.
The base values of voltage, current, pwer and impedance are required to represent the
power system by reactance diagram. Selection of base valuesfor any two of them
determines the base values of the remaining two.
23.What is the need for base values?
The components of power system may operate at different voltage and power levels. It
will be convenient for analysis of power system if the voltage, power, current ratings of
the components of the power system is expressed with referance to a common value
called base value.
24.What is impedance and reactance diagram?
The impedance diagram is the equivalent circuit of power system in which the various
components of power system are represented by their approximate equivalent circuits.
The impedance diagram is used for load flow studies.
The reactance diagram is the simplified equivalent circuit of the power system in which
the various components are represented by their reactance. The reactance ddiagram can
be obtained from impedance diagram if all the resistive components are neglected.
25. What are the approximations made in impedance diagram?
The neutral reactances are neglected.
The shunt branches in equivalent circuit of induction motor are neglected.
26. What are the approximations made in reactance diagram?
The neutral reactances are neglected.
The resistances are neglected.
All static loads and induction motors are neglected.
27. What is a bus?
The meeting point of various components in a power system is called a bus. The bus
is a conductor made of copper having negligible resistance. The buses are considered as a
points of constant voltage in a system.
28. What is bus admittance matrix?
The matrix consisting of the self and mutual admittances of the network of a power
system is called bus admittance matrix.
29. Name the diagonal and off diagonal elements of bus admittance matrix.
The diagonal elements of bus admittance matrix are called self admittances of the
buses and off diagonal elements are called mutual admittances of the buses.
30. What is bus imbedance matrix?
The matrix consisting of driving point impedances and transfer impedances of the
network of a power system is called bus impedance matrix.
31. Name the diagonal elements and off diagonal elements of bus impedance matrix.
The diagonal elements of bus impedance matrix are called driving point impedances
of the buses and off diagonal elements of bus impedance matrix are called transfer
impedances of the buses.
32.What are the methods available for forming bus impedance matrix.
1. Form the bus impedance matrix and then take its inverse to get bus impedance
matrix.
2. Directly form the bus impedance matrix from the reactance diagram. This
method utilizes the techniques of modifications of existing bus impedance
matrix due to addition of new bus.
32. Write the four ways of adding an impedance to an existing system so as to modify
bus impedance matrix.
1. Adding a branch of impedanceZb from a new bus p to the referance bus.
2. Adding a branch of impedance Zb from a new busp to an existing bus.
3. Adding a branch of impedance Zb from an existing busq to the referance
bus.
4. Adding a branch of impedance Zb between two existing buses h and q.
33.What are symmetrical components?
An unbalanced system of N related vectors can be resolved into N systems of
balanced vectors. The N sets of balanced vectors are called symmetrical
components.
33. Write the symmetrical components of three phase system.
1.positive sequence components
3. negative sequence components.
4. zero sequence components.
34. What are positive sequence components?
The positive sequence components of a three phase unbalanced vectors consists of three
vectors of equal magnatude, displased from each other by 120 in phase and having the
same phase sequence as the original vectors.
35. What are negative sequence components?
The negative sequence components of a three phase unbalanced vectors consists of three
vectors of equal magnitude displaced from each other by 120 degree in phase and having
the phase sequence opposite to that of the original vectors.
36.What are zero sequence components?
The zero sequence components of a three phase unbalanced vectors consists of 3 vectors
of equal magnitude and with zero phase displacement from each other.
36. What are sequence impedance and sequence networks?
The sequence impedances are the impedances offered by the devices for the like
sequrnce component of the current.The single phase equivalent circuit of a power system consists of impedances to current f any one sequence is called sequence network.
37.What is meant by positive, negative and zero sequence impedance.
The impedance of the circuit element for positive, negative and zero sequence
component currents are called positive, negative and zero sequence impedances resp.
38.What is meant by positive, negative and zero sequence reactance.
The reactance diagram of a power system, when formed using positive, negative and
zero sequence reactances are called positive, negative and zero sequence reactance
diagram resp.
39.What is load flow or power flow study?
The study of various methods of solution to power system network is reffered to as load
flow study. The solution provides the voltages at various buses, power flowing in various
lines and line losses.
40.What are the information that are obtained from a load flow study.
The information obtained from a load flow study are magnatude and phase of bus
voltages,real and reactive power flowing in each line and the line losses. T he load flow
solution also gives the initial conditions of the system when the transient behaviour of
the system to be studied.
41.What is the need for load flow study.
The load flow study of a power system is essential to decide the best operation existing
system and for planning the future expansion of the system. It is also essential for
designing the power system.
42. What are the quantities associated with each bus ina system?
Each bus in a power system is associated with four quantities and they are real power,
reactive power, magnitude of voltage, and phase angle of voltage.
43. What are the different types of buses.
Load bus,generator bus,slack bus.
44.Define voltage controlled bus?
A bus is called voltage controlled bus if the magnitude of volte\age and real power are
specified for it. In a voltage controlled bus the magnitude of the voltage is not allowed to
change.
45. What is PQ bus?
A bus is called PQ bus when real and reactive components of power are specified for the
bus. In a load bus the voltage is allowed to vary within permissible limits.
46. What is swing bus?
Abus is called swing bus when the magnitude and phase of the bus voltage are specified
for it. The swing bus is the referance bus for load flow solution and it is required for
accounting line losses. Usually one of the generator bus is selected as swing bus.
47.What is the need for slack bus?
The slack bus is needed to account for transmission line losses. In a power system the
total power generated will be equal to sum of power consumed by loads and losses. In a
power system only the generated power and load power are specified for buses. The
slack bus is assumed to generate the power required for losses. Since the losses are
unknown the real and reactive power are not specified for slack bus.
48.What are the operating constraints imposed in the load flow studies?
The operating constraints imposed in load flow studies are reactive power limits for
generator buses and allowable change in magnitude of voltagefor load buses
.
49What are the iterative methods mainly used for solution of load flow study.
The Guass sedal method and Newton Raphson method are the two iterative methods.
50.Discuss the effect of acceleration factor in load flow study.
The acceleration factor is a real quantity and it modify the magnitude of voltage alone.
51What is meant by flat voltage start.
In iterative methods of load flow solution, the initial voltages of all buses exept slack bus
are assumed as 1+j0 pu.This is reffered as flat voltage profile.
52.When the generator buses are treated as load bus.
If the reactive power constraints of a generator bus violates the specified limits then the
generator is treated as load bus.
53. What will be the reactive power and bus voltage whan the generator bus is treated as
load bus.When the generator bus is treated as load bus, the reactive power of the bus is equated to
the limit it has violated, and the previous iteration value of bus voltage is used for
calculating current iteration value.
54. What are the advantages of Guass sedal methoa?
Calculations are simple and so the programming task is lesses.
The memory requirement is less
Useful for small systems
55 What are the disadvantages of Guass seidal method?
Requires large no. of iterations to reach converge
Not suitable for large systems
Convergence time increases with size of the system
56. How approximations is performed in Newton Raphson method?
In N-R method, the set of nonlinear simultaneous equations are approximated to a set of
linear simultaneous equations using tailors series expansion and the terms are limited to
first order approximation.
57.What is Jacobian matrix? How the elements of Jacobian matrix are computed.
The matrix formed from the first derivatives of load flow equations is called Jacobian
matrix.The elements of Jacobian matrix will change in every itration. In each iteration the
elements of the jacobian matrix are obtained by partially differentiating the load flow
equations w.r. t a unknown variable and then evaluating the first derivatives using the
solution of previous iteration
58.What are the adv. Of N-R method?
The N-R method is faster, more reliable and the results are accurate.
Requires less no. of iterations
Suitable for large size system
59. What are the disadv. Of N-R method?
The programming is more complex
The memory requirement is more
60 What is off nominal turns ratio?
When the voltage or turns ratio of a transformer is not used to decide the ratio of base
KV then its voltage ratio is called off nominal turns ratio. Usually the voltage ratio of
regulating transformer will be off nominal ratios
.
61 What is meant by a fault?
A fault in a circuit is any failure which interferes with the normal flow of current. The
faults are associated with abnormal change in current, voltage and frequency of the
power systwm. The faults may cause dan\mage to the equipments if it is allowed to persit
for a long time. Hence every part of the system has been protected by means of relays
and circuir breakers to sence the faults to isolate the faulty part from the healthy part in
the event of fault.
62Why fault accurs in a power system?
The fault occur in a power system due to insulation failure of equipments, flashover of
lines initiated by a lightning stroke, due to permanent damage to conductors and towers
63. How are faults are classified?
The faults are classified as shunt and series faults. The shunt faults are due to short
circuits in conductors and the series faults are due to oped conductors.
64.List the various types of series and shunt fault?
Shunt faults are,
Line to ground fault line to line fault, double line to ground fault, three phase fault.
Series faults are,
One open conductor fault
Two open conductor fault
64 What is symmetrical and unsymmetrical fault?
The fault is called symmetrical fault if the fault current is equal in all the phases. The
fault is called unsymmetrical fault if the fault current is not equal in all the phases.
65. Name any two methods of reducing short circuit current/
By providing neutral reactance.
By introducing a large value of shunt reactance between buses.
66. What is meant by fault calculations/
The fault condition of a power system can be dived into subtransient, transient and steady
state periods. The currents in the various parts of the system and in the fault are different
in these periods. The estimation of these currents for various types of faults at various
locations in the system are commenly reffered as fault calculations.
67.Define stability?
The stability of a system is defined as the ability of power system to return to stable
operation when it is subjected to a disturbance.
68. Define steady state stability
The stady statenstability is defined as the ability of a system to remain stable for small
disturbance.
69. Define transient stability?
The transient stabilitymis defined as the abilitymof a system to remain stable for large
disturbance.
70What is steady state state stability limit?
The steady state stability limit is the max. power that can be transferred by a machine toa
receving system without loss of synchronism.71 Define swing curve? What is the use of
swing curve.The swing curve is the plot between the power angle and time. It is usually plotted for a
transient state to stydy the nature of variation in angle for a sudden large disturbance.
71.Define power angle/
The power angle is defined as the angular displacement of the rotor from synchronously
rotating referance frame.
72Define critical clearing time and critiacal clearing angle
The critical clearing angle is the max. allowable change in the power angle before
clearing the fault, without loss of synchronism.
The critical clearing time can be defined as thw max. time delay that can be allowed to
clear a fault without loss of synchronism.
73.Define equal area criterion?
The equal area criterion for stability states that the system is stable if the area under pvs
angle curve reduces to zero at some value of angle.
74.What is transient state stability limit?
The transient state stability limit is the max. power that can be transmitted by a machine
to a receiving system without loss of synchronism.In steady state the power transferred
by synchronous machine is always less than the steady state stability limit.
75.what is transient stability limit ?
The transient stability limit is the max power that can be transmitted by a machine to a
fault or a receiving system during a transient state without loss of synchronism.The
transient stability limit is always less than the steady state stability limit.
Monday, December 7, 2009
current affairs 2009
1. Which country won Nehru Cup International Football Tournament 2009?
India defeated Syria by 5-4 (penalty shootout) in the finals on August 31, 2009.
Goal-keeper Subroto Paul, who saved three penalties to become India’s saviour, was awarded the man of the match of the final.
India won this cup two times, 2007 & 2009.
2. Who won the Man of the Tournament award of Nehru Cup Football title-2009?
Bhaichung Bhutia, Indian Captain
3. Which scientist is elected as the new President of International Academy of Astronautics (IAA)?
Dr. Madhavan Nair, Chief of Indian Space Research Organisation (ISRO).
4. Who is the new Air Officer Commanding –in-Chief of Southern Air Command of India?
Air Marshal Sumit Mukerjee. He is the only pilot in the history of IAF to have commanded units with the Mig-21,Mig-23U, Mig-25, Mig-27 and Mig-29 aircraft.
5. Who is appointed as the Flag Officer Commanding-in-Chief of the Southern Naval Command?
Vice-Admiral K.N. Sushil
6. Who will act as a bowling consultant for the Kolkata Knight Riders during the third edition of the Indian Premier League (IPL) next year?
Vasim Akram
7. India achieved a Gross Domestic Product (GDP) growth rate of how much percentage during April-June 2009?
6.1%
8. The Indian-American fashion designer who charged with sexually assaulting seven girls was sentenced to 59 years of imprisonment on Aug 31?
Anand Jon Alexander
9. Who is appointed as the new Air Officer-in-Charge Personnel (AOP)of the Indian Air Force (IAF)?
Air Marshal KJ Mathews
10. Country which has been expelled from the Commonwealth after failing to announce plans to hold elections in 2010?
Fiji
11. Distinguished scientist and the man in charge of the development of missile and strategic systems in the country, who is appointed as the chief of the Defence Research and Development Organisation(DRDO)?
Dr Vijay Kumar Saraswat
12. Who is appointed as the vice chief of Indian Army?
Lt General P C Bhardwaj
13. Bollywood Actor who has been appointed by Life insurance Company Max New York Life as the brand ambassador for Max Vijay, a brand specifically targeted at providing financial inclusion to the underprivileged masses?
Amitabh Bachchan
14. Andhra Pradesh Chief Minister who feared dead after his Bell 430 chopper crash-landed about 40 nautical miles east of the Kurnool mountainous area of Andra Pradesh?
Y.S. Rajasekhara Reddy
15. The first Iranian female cabinet minister who is appointed since the foundation of the Islamic Republic 30 years?
Marzieh Vahid Dastjerdi
Iranian parliament approves Marzieh as new health minister despite opposition from hardline MPs and clerics.
16. Who won the Man of the Series Award in the recent 20-20 cricket series between Sri Lanka and New Zealand which is held in Sri Lanka?
Jesse Ryder(New Zealand).
New Zealand won the series by 2-0.
17. Lok Sabha Secretary General who was recently given a year's extension by Lok Sabha Speaker Meira Kumar?
P.D.T. Acharya
18. Who took over charge as Additional General Manager, Southern Railway?
Shri A.K. Gupta
19. Athletes who won $1 million Golden League jackpot which is given by IAAF (International Association of Athletics Federations) to anyone who wins all six of the premier European meets?
(All gold Yelena Isinbayeva, Kenenisa Bekele and Sanya Richards Getty Images)
Answer:Yelena Isinbayeva, Kenenisa Bekele and Sanya Richards
20. Who is the new Brand Ambassador of popular Levis Jeans?
Priyanka Chopra.
21. U.S.President Barack Obama's adviser and an administration official specializing in environmentally friendly "green jobs" with the White House Council on Environmental Quality who resigned amid controversy over past inflammatory statements?
Van Jones
22. Who has topped the list of world's 10 top earning cricketers compiled by Forbes magazine ?
Mahendra Singh Dhoni, Indian skipper
Raking in USD 10 million, Dhoni is at the top of the chart followed by Tendulkar at the second spot with earnings worth USD 8 million in the list of 'The World's Top-Earning Cricketers' . While Yuvraj Singh and Dravid are at the third and fourth spot, respectively, Ganguly and Australian cricketer Ricky Ponting share the sixth place.
23. Former Chief Minister of Punjab and former governor of Haryana and Orissa , who died recently after a prolonged illness?
Harcharan Singh Brar
25. Who has become the second Indian after Geet Sethi to win the World’s Billiards Championship?
Pankaj Advani
He beat defending champion Mark Russel 2030-1253 to win the World Professional Billiards Championship-2009. Geet Sethi won the title in 1992.
26. Australian Cricket player who retired from international Twenty20 cricket recently?
Ricky Ponting
27. The first African country to qualify for the 2010 World Cup Football which is to be held in South Africa?
Ghana
28. Which country leads world in foreign weapons sales in the year 2008?
United States of America. America accounted for more than two-thirds of foreign weapons sales in 2008.
29. Who participated as the chief guest at the 19th Independence Day celebrations of Tajikistan which was held at Dushanbe?
Pratibha Patil, President of India
30. Reserve Bank recently decided to introduce polymer banknotes of which denomination whose life span would be 4 times the normal currency notes and would be difficult to imitate.?
Rs 10
Polymer notes were first introduced in Australia to safeguard against counterfeiting of currency
31. The Sri Lankan government has ordered a senior United Nations diplomat to leave the country after accusing him of partiality towards the Liberation Tigers of Tamil Eelam (LTTE). Name of that spoke person of UNICEF?
James Elder, an Australian national.
32. Woman journalist of Sudan convicted of public indecency for wearing trousers outdoors was freed recently despite her own desire to serve a month in prison as protest against Sudan's draconian morality laws?
Lubna Hussein
33. Name of the Buddha statue gifted by Mahatma Gandhi to one of his Irish friend, which was sold in London in the auction for Rs 5.47 lakh (6,840 pounds)?
Bodhisattva.
The statue was possibly of the Bodhisattva of compassion Avalokitesvara, a seated 13-inch-high bronze Buddha statue.
Gandhiji gave this statue to his Irish friend Emma Harker when she volunteered for relief work among the poor in flooded areas of Bihar and Orissa.
34. Who was the captain of Indian team for the 23rd FIBA Asia Women Basketball Championship held in Chennai?
Geethu Anna Jose
35. Venezuela recognized the independence of two countries on September 10, 2009. Name that countries.
South Ossetia and Abkhazia.
Earlier, Russia and Nicaragua also recognized independence of Abkhazia and South Ossetia.
36. New York Governor David Paterson recently signed into law a bill that bans use of a word in documents used by state agencies, public authorities and municipalities when referring to persons of Asian or Pacific islander heritage.
Which word?
"Oriental"
37. Indian Musician who has been invited to perform live along with the famous Pussycat Dolls — a pop girl group and dance ensemble- on the occasion of the India’s historic participation in the America’s world famous Polo Cup?
A.R.Rahman
38. Former Taiwan President who has been found guilty of corruption and sentenced to life in prison?
Chen Shui-bian
39. Indian film which is included in the “Festival of festival” section in the Cairo International film festival that will commence on the tenth of November?
Raman. The film is directed by Dr.Biju.
40. Which footballer won the annual VP Sathyan Memorial Award?
Mohanraj
Chennai-based, Kerala Sports Persons Association (KESPA) has picked Tamil Nadu footballer Mohanraj for this award.
41. Former president of BCCI who served as the chairman of the national selection committee (including when Sachin Tendulkar was first picked in the Indian team in 1989) died at the age of 73 following a prolonged illness recently?
Raj Singh Dungarpur
42. High Court Lawyer, who has been appointed Assistant Solicitor General of India for conducting Central government cases other than the cases of income tax and the Railway Department before the High Court?
T.P.M. Ibrahim Khan
43. An island of Mexico which was clearly visible on national and international maps until the middle of the 20th century has gone missing now?
Bermeja Island. This island is strategically important as it could give Mexico a claim to millions of dollars worth of oil deposits.
44. Cuban revolutionary leader, who has died in Havana at the age of 82, had been among only three surviving rebel leaders who still bore the honorary title “Commander of the Revolution.”
Juan Almeida Bosque
45. World's oldest person, a woman who was born in 1894 died in California at the age of 115 gained a measure of fame when she voted for Barack Obama for U.S. president?
Gertrude Baines
46. Which country will host the 6th SAF football matches scheduled for December 1-15 of this year?
Bangladesh. Eight teams of South Asian countries will take part in these matches.
47. First Indian to reach semi-finals of World Boxing Championships and fist Indian to win a medal in the same event?
Vijender Kumar
He won Bronze medal in the World Boxing Championships and becomes the first Indian to do so.
48. Which club won their maiden IFA Shield football tournament title?
Churchill Brothers, Goa
They beating local giant Mohun Bagan 2-0
49. Nat West One day cricket series between England and Australia won by ?
Australia. They won the series 6-1.
50. Who has been selected for this year’s Mathrubhumi Literary Award of Rs.2 Lakhs instituted by the Malayalam daily “Mathrubhumi”?
Kovilan
51. Name of the 14-year-old astrophysicist from Kozhikode, Kerala who recently participated in the NASA space camp where a model rocket designed by her was launched?
Hannan Binth Hashim.
She has prepared a research paper titled ‘Absolute Theory of Zero' which questions the accuracy of many existing theories like Albert Einstein's ‘Theory of relativity' and the ‘Big Bang Theory'.
52. An American agronomist, humanitarian, and Nobel laureate who has been deemed the father of the Green Revolution died at the age of 95, on September 12, 2009?
Norman Borlaug.
He was one of only six people to have won the Nobel Peace Prize, the Presidential Medal of Freedom and the Congressional Gold Medal. He was also a recipient of the Padma Vibhushan, India's second-highest civilian honor.
53. Which film won the Golden Lion for best picture at the Venice film festival?
"Lebanon"
Hard-hitting Israeli war movie "Lebanon" is directed by Samuel Maoz
Best Actor Award: Colin Firth
Best Actress Award: Ksenia Rappoport
54. Who won the Silver Lion prize for best director at the Venice film festival?
Shirin Neshat
She won this award for the film "Women without Men," based on a banned book about Iran in the 1950s.
55. ‘Basava Sri’ award instituted by Murugha mutt won by ?
P.T.Usha.
56. Noted football commentator who was found dead in his hotel a day after the final of the IFA Shield?
Noel De Lima Leitao
57. French photographer who was one of France's giants of photography, particularly famous for his images of post-war Paris in the 1940s and 1950s died recently at the age of 99?
Willy Ronis
58. Who has been named as one of the two Anglo Indian nominees to the Lok Sabha -- taking Kerala's strength in the Lower House of the Indian Parliament to 21?
Charles Dias.
59. Which country won the tri-nation Compaq Cup (One Day Cricket Series) held in Sri Lanka?
India.
India beat Sri Lanka in the final by 46 runs. New Zealand was the third team.
Sachin Tendulkar won Man of the Match Award for his 138 runs in final.
Man of the Series: Sachin Tendulkar
60. Who is appointed as the Managing Director of Agri co-operative National Agricultural Cooperative Marketing Federation of India Limited (NAFED)?
C V Ananda Bose
61. The India Today Group has recently adjudged which state of India as the best State with regard to the law and order situation.
Kerala
62. Who won US Open Men’s Double Title?
Leander Paes and Lukas Dlouhy
They won the Grand Slam title after defeating Mahesh Bhupathi and Mark Knowles in the US Open men’s doubles final. This is 10th Grant slam title for Leander Paes.
63. Who won the US Open Women’s title 2009?
Kim Clijsters
She beat 19-year-old Caroline Wozniacki of Denmark, 7-5, 6-3, in the final.
She become the first unseeded woman to win the US Open and the first mother to win a major title since 1980.
64. Who Clinch US Open Women’s Doubles Title?
Serena Williams and Venus Williams
They took over top seeds Cara Black of Zimbabwe and Liezel Huber of the United States in straight sets of 6-2, 6-2 to clinch the women’s doubles title at US Open.
65. Who won US Open men's title?
Juan Martin del Potro
Juan Martin del Potro of Argentina battled back to beat five-times champion Roger Federer 3-6, 7-6, 4-6, 7-6, 6-2 in the final
66. A juror in the fashion designer Anand Jon rape trial who was fined $1,000 and sentenced to 120 hours of community service for trying to strike up a romance with Sanjana, the sister of Anand Jon who was sentenced to 59 years?
Alvin Dymally
67. Who has been selected by the Audit Bureau of Circulations (ABC) to head the operations of the organisation as the Chairman for the period of 2009-10?
Mr Subroto Chattopadhyay
68. Name of the Olympic medal-winning boxer who has been found dead by his manager?
Darren Sutherland
Sutherland has won a bronze medal for Ireland at the 2008 Beijing Olympics.
69. Who will be the chairman of the Fourth Finance Commission constituted by the Government of Kerala?
Dr.M.A.Umman
70. Name of the sacred food offered to devotees at the Lord Venkateswara Temple in Andhra Pradesh which has been awarded geographical copyright that bars others from naming or marketing the sweetmeat preparation under the same name?
Tirupati laddoo
71. Name of the most expensive bike so far launched in India by the Japanese bike giant Yamaha?
Yamaha VMAX
This 1,680cc super bike VMAX, priced at Rs. 20 lakh (ex-showroom Delhi).
72. Person from Kerala who has been honored with the highest award of Bharat Scouts and Guides ‘Silver Elephant Award 2007-08’.?
Shri M. C. Ramadas
73. Who is named as Japan's new Prime Minister
Yukio Hatoyama. He will be named the 93rd Prime Minister of Japan.
74. Indonesia's most wanted Islamist militant, who was killed in a police shoot-out in Central Java of Indonesia ?
Noordin Mohammad Top.
75. Who is now officially the tallest man walking the planet by the Guinness World Records?
(REUTERS Andrew Winning)
Sultan Kosen 27, from Turkey was recognized as the tallest person(8 foot 1 inch (2.47 meter)) in the world on September 17,2009.
76. Who is the new Accountant General of Kerala State?
Maha Lekshmi Menon
77. Indian American technocrat who has been appointed by U.S.President Barack Obama to a key administration post dealing with energy research?
Arun Majumdar
78. Footballer of Argentina who signed a two-year contract extension with Barcelona until the summer of 2016.
Lionel Messi
79. The Indians who have figured in a list of 60 "most influential foreigners" who have played a profound role in shaping the way over 1.2-billion people of modern China think and live?
Jawaharlal Nehru and Rabindranath Tagore
80. Which TV series won the 2009 Emmy award for best comedy?
30 Rock.
81. Which TV series won the 2009 Emmy award for best drama?
Mad Men
82. Who is the new captain of Delhi Dare Devils Team ?
Gautham Gambhir
83. The Indian tennis star who has confirmed Indian team berth in the Davis Cup World Group after he ousted South Africa's Rik Voest in the reverse singles match of the Davis Cup tie ?
Somdev Dewarman
Indian team has made into World Group playoff after a long period of 11 years.
84. Name of 13-year-old girl from Lucknow who addressed the United Nations Climate Change Summit in New York?
Yugratna Srivastav
85. Who are the winners of Durand Cup-2009?
Churchill Brothers. They beat Mohun Bagan in the final. Churchill Brothers had earlier won the trophy in 2007
86. Name of Indian-origin woman who was sentenced to 33 years in jail - one of the longest jail terms handed out to a woman in Britain - for murdering her two teenaged daughters in a frenzied knife attack at her home in Cambridgeshire?
Rekha Kumari-Baker
87. The 63-year-old magazine, which has covered business and politics since World War II, will shut down in December 2009, struggling with losses as readers and advertisers move to the Internet?
“Far Eastern Economic Review”
88. Name of India's 16th remote sensing satellite successfully launched by ISRO through its space carrier Plar Satellite Launch Vehicle (PSLV) in just twenty minutes?
Oceansat-2.
ISRO's Polar Satellite Launch Vehicle, PSLV-C14 successfully launched the 960 kg Indian remote sensing satellite Oceansat-2 and six nano satellites for international customers into a polar Sun Synchronous Orbit (SSO). This was the fifteenth successful flight of PSLV.
89. Who has been selected for this year’s Vallathol Award which carries a purse of Rs.1,11,111 and citation?
Kavalam Narayana Panicker
90. The much anticipated small car for India which was unveiled in Delhi by Ford Motor Company?
Ford Figo
91. Who is the new director of United Nations Educational, Scientific and Cultural Organization, (UNESCO)?
Irina Bokova, Bulgarian diplomat
92. The adventurers who set a new world record after successfully landing on Mount Everest 16,800 ft above sea level?
Ramesh Chandra Tripathi, Leo Dickinson and Ralph Mitchell.
They jumped from an altitude of 20,000 ft to land at the world’s highest drop zone, near Mount Everest.
93. A prominent Indian American agricultural scientist, who has been nominated for the post of the Chief Agricultural Negotiator in the Office of the U.S. Trade Representative by the US President Barack Obama?
Islam A. Siddiqui
94. India's maiden spacecraft, which has discovered water on the lunar surface?
Chandrayaan-1
95. First mixed-gender university of Saudi Arabia which opened recently?
King Abdullah University of Science and Technology (KAUST)
96. Who is the chairman of Subordinate Legislation Committee of Indian Loksabha?
P.Karunakaran , M.P from Kerala
97. Which country won the 23rd Asian Women's Basketball Championships held in Chennai, India?
China. They beat South Korea in the final
98. Indian who won bronze medal in the freestyle 74 kg category in the prestigious World Wrestling Championship held in Denmark?
Ramesh Kumar
India made history in wrestling after a gap of 32 years, when Ramesh Kumar won bronze medal in World Wrestling Championship.
99. Who was elected president of the Indian Newspaper Society for 2009-10, at the 70th annual general meeting of the INS?
T. Venkattram Reddy. He is the chairman of the Hyderabad-based Deccan Chronicle.
100. Who will head the Committee of Privileges which has been reconstituted by Lok Sabha Speaker Meira Kumar?
P.C.Chacko, M.P.from Kerala
101. Britain’s Indian-origin Business Minister, who is set to step down, appointed as the UK’s representative to G-20?
Shriti Vadera
102. Who was elected as regional chairman (Kerala)of the Indian Newspaper Society for 2009-10?
P.V.chandran
103. Which political party retained power in Portuguese elections recently ?
Center-left Socialist Party.
Portuguese Prime Minister Jose Socrates is the main leader of this party.
104. German Chancellor who recorded a resounding triumph in her country's recent general elections?
Angela Merkel
105. Indian-American Human rights activist who has won the American Courage Award for her human rights work in India and the United States?
Mallika Dutt
106. Name of the limited-series pen by Pen-makers Mont Blanc inspired by Gandhiji’s iconic Dandi March in 1930 to protest against the British salt tax ?
Mahatma Gandhi Limited Edition-241 series (MGLE-241)
This pen costs Rs 11.39 lakh.
107. Who won the women’s singles title in the Yonex Czech international badminton championship?
Trupti Murgunde
India defeated Syria by 5-4 (penalty shootout) in the finals on August 31, 2009.
Goal-keeper Subroto Paul, who saved three penalties to become India’s saviour, was awarded the man of the match of the final.
India won this cup two times, 2007 & 2009.
2. Who won the Man of the Tournament award of Nehru Cup Football title-2009?
Bhaichung Bhutia, Indian Captain
3. Which scientist is elected as the new President of International Academy of Astronautics (IAA)?
Dr. Madhavan Nair, Chief of Indian Space Research Organisation (ISRO).
4. Who is the new Air Officer Commanding –in-Chief of Southern Air Command of India?
Air Marshal Sumit Mukerjee. He is the only pilot in the history of IAF to have commanded units with the Mig-21,Mig-23U, Mig-25, Mig-27 and Mig-29 aircraft.
5. Who is appointed as the Flag Officer Commanding-in-Chief of the Southern Naval Command?
Vice-Admiral K.N. Sushil
6. Who will act as a bowling consultant for the Kolkata Knight Riders during the third edition of the Indian Premier League (IPL) next year?
Vasim Akram
7. India achieved a Gross Domestic Product (GDP) growth rate of how much percentage during April-June 2009?
6.1%
8. The Indian-American fashion designer who charged with sexually assaulting seven girls was sentenced to 59 years of imprisonment on Aug 31?
Anand Jon Alexander
9. Who is appointed as the new Air Officer-in-Charge Personnel (AOP)of the Indian Air Force (IAF)?
Air Marshal KJ Mathews
10. Country which has been expelled from the Commonwealth after failing to announce plans to hold elections in 2010?
Fiji
11. Distinguished scientist and the man in charge of the development of missile and strategic systems in the country, who is appointed as the chief of the Defence Research and Development Organisation(DRDO)?
Dr Vijay Kumar Saraswat
12. Who is appointed as the vice chief of Indian Army?
Lt General P C Bhardwaj
13. Bollywood Actor who has been appointed by Life insurance Company Max New York Life as the brand ambassador for Max Vijay, a brand specifically targeted at providing financial inclusion to the underprivileged masses?
Amitabh Bachchan
14. Andhra Pradesh Chief Minister who feared dead after his Bell 430 chopper crash-landed about 40 nautical miles east of the Kurnool mountainous area of Andra Pradesh?
Y.S. Rajasekhara Reddy
15. The first Iranian female cabinet minister who is appointed since the foundation of the Islamic Republic 30 years?
Marzieh Vahid Dastjerdi
Iranian parliament approves Marzieh as new health minister despite opposition from hardline MPs and clerics.
16. Who won the Man of the Series Award in the recent 20-20 cricket series between Sri Lanka and New Zealand which is held in Sri Lanka?
Jesse Ryder(New Zealand).
New Zealand won the series by 2-0.
17. Lok Sabha Secretary General who was recently given a year's extension by Lok Sabha Speaker Meira Kumar?
P.D.T. Acharya
18. Who took over charge as Additional General Manager, Southern Railway?
Shri A.K. Gupta
19. Athletes who won $1 million Golden League jackpot which is given by IAAF (International Association of Athletics Federations) to anyone who wins all six of the premier European meets?
(All gold Yelena Isinbayeva, Kenenisa Bekele and Sanya Richards Getty Images)
Answer:Yelena Isinbayeva, Kenenisa Bekele and Sanya Richards
20. Who is the new Brand Ambassador of popular Levis Jeans?
Priyanka Chopra.
21. U.S.President Barack Obama's adviser and an administration official specializing in environmentally friendly "green jobs" with the White House Council on Environmental Quality who resigned amid controversy over past inflammatory statements?
Van Jones
22. Who has topped the list of world's 10 top earning cricketers compiled by Forbes magazine ?
Mahendra Singh Dhoni, Indian skipper
Raking in USD 10 million, Dhoni is at the top of the chart followed by Tendulkar at the second spot with earnings worth USD 8 million in the list of 'The World's Top-Earning Cricketers' . While Yuvraj Singh and Dravid are at the third and fourth spot, respectively, Ganguly and Australian cricketer Ricky Ponting share the sixth place.
23. Former Chief Minister of Punjab and former governor of Haryana and Orissa , who died recently after a prolonged illness?
Harcharan Singh Brar
25. Who has become the second Indian after Geet Sethi to win the World’s Billiards Championship?
Pankaj Advani
He beat defending champion Mark Russel 2030-1253 to win the World Professional Billiards Championship-2009. Geet Sethi won the title in 1992.
26. Australian Cricket player who retired from international Twenty20 cricket recently?
Ricky Ponting
27. The first African country to qualify for the 2010 World Cup Football which is to be held in South Africa?
Ghana
28. Which country leads world in foreign weapons sales in the year 2008?
United States of America. America accounted for more than two-thirds of foreign weapons sales in 2008.
29. Who participated as the chief guest at the 19th Independence Day celebrations of Tajikistan which was held at Dushanbe?
Pratibha Patil, President of India
30. Reserve Bank recently decided to introduce polymer banknotes of which denomination whose life span would be 4 times the normal currency notes and would be difficult to imitate.?
Rs 10
Polymer notes were first introduced in Australia to safeguard against counterfeiting of currency
31. The Sri Lankan government has ordered a senior United Nations diplomat to leave the country after accusing him of partiality towards the Liberation Tigers of Tamil Eelam (LTTE). Name of that spoke person of UNICEF?
James Elder, an Australian national.
32. Woman journalist of Sudan convicted of public indecency for wearing trousers outdoors was freed recently despite her own desire to serve a month in prison as protest against Sudan's draconian morality laws?
Lubna Hussein
33. Name of the Buddha statue gifted by Mahatma Gandhi to one of his Irish friend, which was sold in London in the auction for Rs 5.47 lakh (6,840 pounds)?
Bodhisattva.
The statue was possibly of the Bodhisattva of compassion Avalokitesvara, a seated 13-inch-high bronze Buddha statue.
Gandhiji gave this statue to his Irish friend Emma Harker when she volunteered for relief work among the poor in flooded areas of Bihar and Orissa.
34. Who was the captain of Indian team for the 23rd FIBA Asia Women Basketball Championship held in Chennai?
Geethu Anna Jose
35. Venezuela recognized the independence of two countries on September 10, 2009. Name that countries.
South Ossetia and Abkhazia.
Earlier, Russia and Nicaragua also recognized independence of Abkhazia and South Ossetia.
36. New York Governor David Paterson recently signed into law a bill that bans use of a word in documents used by state agencies, public authorities and municipalities when referring to persons of Asian or Pacific islander heritage.
Which word?
"Oriental"
37. Indian Musician who has been invited to perform live along with the famous Pussycat Dolls — a pop girl group and dance ensemble- on the occasion of the India’s historic participation in the America’s world famous Polo Cup?
A.R.Rahman
38. Former Taiwan President who has been found guilty of corruption and sentenced to life in prison?
Chen Shui-bian
39. Indian film which is included in the “Festival of festival” section in the Cairo International film festival that will commence on the tenth of November?
Raman. The film is directed by Dr.Biju.
40. Which footballer won the annual VP Sathyan Memorial Award?
Mohanraj
Chennai-based, Kerala Sports Persons Association (KESPA) has picked Tamil Nadu footballer Mohanraj for this award.
41. Former president of BCCI who served as the chairman of the national selection committee (including when Sachin Tendulkar was first picked in the Indian team in 1989) died at the age of 73 following a prolonged illness recently?
Raj Singh Dungarpur
42. High Court Lawyer, who has been appointed Assistant Solicitor General of India for conducting Central government cases other than the cases of income tax and the Railway Department before the High Court?
T.P.M. Ibrahim Khan
43. An island of Mexico which was clearly visible on national and international maps until the middle of the 20th century has gone missing now?
Bermeja Island. This island is strategically important as it could give Mexico a claim to millions of dollars worth of oil deposits.
44. Cuban revolutionary leader, who has died in Havana at the age of 82, had been among only three surviving rebel leaders who still bore the honorary title “Commander of the Revolution.”
Juan Almeida Bosque
45. World's oldest person, a woman who was born in 1894 died in California at the age of 115 gained a measure of fame when she voted for Barack Obama for U.S. president?
Gertrude Baines
46. Which country will host the 6th SAF football matches scheduled for December 1-15 of this year?
Bangladesh. Eight teams of South Asian countries will take part in these matches.
47. First Indian to reach semi-finals of World Boxing Championships and fist Indian to win a medal in the same event?
Vijender Kumar
He won Bronze medal in the World Boxing Championships and becomes the first Indian to do so.
48. Which club won their maiden IFA Shield football tournament title?
Churchill Brothers, Goa
They beating local giant Mohun Bagan 2-0
49. Nat West One day cricket series between England and Australia won by ?
Australia. They won the series 6-1.
50. Who has been selected for this year’s Mathrubhumi Literary Award of Rs.2 Lakhs instituted by the Malayalam daily “Mathrubhumi”?
Kovilan
51. Name of the 14-year-old astrophysicist from Kozhikode, Kerala who recently participated in the NASA space camp where a model rocket designed by her was launched?
Hannan Binth Hashim.
She has prepared a research paper titled ‘Absolute Theory of Zero' which questions the accuracy of many existing theories like Albert Einstein's ‘Theory of relativity' and the ‘Big Bang Theory'.
52. An American agronomist, humanitarian, and Nobel laureate who has been deemed the father of the Green Revolution died at the age of 95, on September 12, 2009?
Norman Borlaug.
He was one of only six people to have won the Nobel Peace Prize, the Presidential Medal of Freedom and the Congressional Gold Medal. He was also a recipient of the Padma Vibhushan, India's second-highest civilian honor.
53. Which film won the Golden Lion for best picture at the Venice film festival?
"Lebanon"
Hard-hitting Israeli war movie "Lebanon" is directed by Samuel Maoz
Best Actor Award: Colin Firth
Best Actress Award: Ksenia Rappoport
54. Who won the Silver Lion prize for best director at the Venice film festival?
Shirin Neshat
She won this award for the film "Women without Men," based on a banned book about Iran in the 1950s.
55. ‘Basava Sri’ award instituted by Murugha mutt won by ?
P.T.Usha.
56. Noted football commentator who was found dead in his hotel a day after the final of the IFA Shield?
Noel De Lima Leitao
57. French photographer who was one of France's giants of photography, particularly famous for his images of post-war Paris in the 1940s and 1950s died recently at the age of 99?
Willy Ronis
58. Who has been named as one of the two Anglo Indian nominees to the Lok Sabha -- taking Kerala's strength in the Lower House of the Indian Parliament to 21?
Charles Dias.
59. Which country won the tri-nation Compaq Cup (One Day Cricket Series) held in Sri Lanka?
India.
India beat Sri Lanka in the final by 46 runs. New Zealand was the third team.
Sachin Tendulkar won Man of the Match Award for his 138 runs in final.
Man of the Series: Sachin Tendulkar
60. Who is appointed as the Managing Director of Agri co-operative National Agricultural Cooperative Marketing Federation of India Limited (NAFED)?
C V Ananda Bose
61. The India Today Group has recently adjudged which state of India as the best State with regard to the law and order situation.
Kerala
62. Who won US Open Men’s Double Title?
Leander Paes and Lukas Dlouhy
They won the Grand Slam title after defeating Mahesh Bhupathi and Mark Knowles in the US Open men’s doubles final. This is 10th Grant slam title for Leander Paes.
63. Who won the US Open Women’s title 2009?
Kim Clijsters
She beat 19-year-old Caroline Wozniacki of Denmark, 7-5, 6-3, in the final.
She become the first unseeded woman to win the US Open and the first mother to win a major title since 1980.
64. Who Clinch US Open Women’s Doubles Title?
Serena Williams and Venus Williams
They took over top seeds Cara Black of Zimbabwe and Liezel Huber of the United States in straight sets of 6-2, 6-2 to clinch the women’s doubles title at US Open.
65. Who won US Open men's title?
Juan Martin del Potro
Juan Martin del Potro of Argentina battled back to beat five-times champion Roger Federer 3-6, 7-6, 4-6, 7-6, 6-2 in the final
66. A juror in the fashion designer Anand Jon rape trial who was fined $1,000 and sentenced to 120 hours of community service for trying to strike up a romance with Sanjana, the sister of Anand Jon who was sentenced to 59 years?
Alvin Dymally
67. Who has been selected by the Audit Bureau of Circulations (ABC) to head the operations of the organisation as the Chairman for the period of 2009-10?
Mr Subroto Chattopadhyay
68. Name of the Olympic medal-winning boxer who has been found dead by his manager?
Darren Sutherland
Sutherland has won a bronze medal for Ireland at the 2008 Beijing Olympics.
69. Who will be the chairman of the Fourth Finance Commission constituted by the Government of Kerala?
Dr.M.A.Umman
70. Name of the sacred food offered to devotees at the Lord Venkateswara Temple in Andhra Pradesh which has been awarded geographical copyright that bars others from naming or marketing the sweetmeat preparation under the same name?
Tirupati laddoo
71. Name of the most expensive bike so far launched in India by the Japanese bike giant Yamaha?
Yamaha VMAX
This 1,680cc super bike VMAX, priced at Rs. 20 lakh (ex-showroom Delhi).
72. Person from Kerala who has been honored with the highest award of Bharat Scouts and Guides ‘Silver Elephant Award 2007-08’.?
Shri M. C. Ramadas
73. Who is named as Japan's new Prime Minister
Yukio Hatoyama. He will be named the 93rd Prime Minister of Japan.
74. Indonesia's most wanted Islamist militant, who was killed in a police shoot-out in Central Java of Indonesia ?
Noordin Mohammad Top.
75. Who is now officially the tallest man walking the planet by the Guinness World Records?
(REUTERS Andrew Winning)
Sultan Kosen 27, from Turkey was recognized as the tallest person(8 foot 1 inch (2.47 meter)) in the world on September 17,2009.
76. Who is the new Accountant General of Kerala State?
Maha Lekshmi Menon
77. Indian American technocrat who has been appointed by U.S.President Barack Obama to a key administration post dealing with energy research?
Arun Majumdar
78. Footballer of Argentina who signed a two-year contract extension with Barcelona until the summer of 2016.
Lionel Messi
79. The Indians who have figured in a list of 60 "most influential foreigners" who have played a profound role in shaping the way over 1.2-billion people of modern China think and live?
Jawaharlal Nehru and Rabindranath Tagore
80. Which TV series won the 2009 Emmy award for best comedy?
30 Rock.
81. Which TV series won the 2009 Emmy award for best drama?
Mad Men
82. Who is the new captain of Delhi Dare Devils Team ?
Gautham Gambhir
83. The Indian tennis star who has confirmed Indian team berth in the Davis Cup World Group after he ousted South Africa's Rik Voest in the reverse singles match of the Davis Cup tie ?
Somdev Dewarman
Indian team has made into World Group playoff after a long period of 11 years.
84. Name of 13-year-old girl from Lucknow who addressed the United Nations Climate Change Summit in New York?
Yugratna Srivastav
85. Who are the winners of Durand Cup-2009?
Churchill Brothers. They beat Mohun Bagan in the final. Churchill Brothers had earlier won the trophy in 2007
86. Name of Indian-origin woman who was sentenced to 33 years in jail - one of the longest jail terms handed out to a woman in Britain - for murdering her two teenaged daughters in a frenzied knife attack at her home in Cambridgeshire?
Rekha Kumari-Baker
87. The 63-year-old magazine, which has covered business and politics since World War II, will shut down in December 2009, struggling with losses as readers and advertisers move to the Internet?
“Far Eastern Economic Review”
88. Name of India's 16th remote sensing satellite successfully launched by ISRO through its space carrier Plar Satellite Launch Vehicle (PSLV) in just twenty minutes?
Oceansat-2.
ISRO's Polar Satellite Launch Vehicle, PSLV-C14 successfully launched the 960 kg Indian remote sensing satellite Oceansat-2 and six nano satellites for international customers into a polar Sun Synchronous Orbit (SSO). This was the fifteenth successful flight of PSLV.
89. Who has been selected for this year’s Vallathol Award which carries a purse of Rs.1,11,111 and citation?
Kavalam Narayana Panicker
90. The much anticipated small car for India which was unveiled in Delhi by Ford Motor Company?
Ford Figo
91. Who is the new director of United Nations Educational, Scientific and Cultural Organization, (UNESCO)?
Irina Bokova, Bulgarian diplomat
92. The adventurers who set a new world record after successfully landing on Mount Everest 16,800 ft above sea level?
Ramesh Chandra Tripathi, Leo Dickinson and Ralph Mitchell.
They jumped from an altitude of 20,000 ft to land at the world’s highest drop zone, near Mount Everest.
93. A prominent Indian American agricultural scientist, who has been nominated for the post of the Chief Agricultural Negotiator in the Office of the U.S. Trade Representative by the US President Barack Obama?
Islam A. Siddiqui
94. India's maiden spacecraft, which has discovered water on the lunar surface?
Chandrayaan-1
95. First mixed-gender university of Saudi Arabia which opened recently?
King Abdullah University of Science and Technology (KAUST)
96. Who is the chairman of Subordinate Legislation Committee of Indian Loksabha?
P.Karunakaran , M.P from Kerala
97. Which country won the 23rd Asian Women's Basketball Championships held in Chennai, India?
China. They beat South Korea in the final
98. Indian who won bronze medal in the freestyle 74 kg category in the prestigious World Wrestling Championship held in Denmark?
Ramesh Kumar
India made history in wrestling after a gap of 32 years, when Ramesh Kumar won bronze medal in World Wrestling Championship.
99. Who was elected president of the Indian Newspaper Society for 2009-10, at the 70th annual general meeting of the INS?
T. Venkattram Reddy. He is the chairman of the Hyderabad-based Deccan Chronicle.
100. Who will head the Committee of Privileges which has been reconstituted by Lok Sabha Speaker Meira Kumar?
P.C.Chacko, M.P.from Kerala
101. Britain’s Indian-origin Business Minister, who is set to step down, appointed as the UK’s representative to G-20?
Shriti Vadera
102. Who was elected as regional chairman (Kerala)of the Indian Newspaper Society for 2009-10?
P.V.chandran
103. Which political party retained power in Portuguese elections recently ?
Center-left Socialist Party.
Portuguese Prime Minister Jose Socrates is the main leader of this party.
104. German Chancellor who recorded a resounding triumph in her country's recent general elections?
Angela Merkel
105. Indian-American Human rights activist who has won the American Courage Award for her human rights work in India and the United States?
Mallika Dutt
106. Name of the limited-series pen by Pen-makers Mont Blanc inspired by Gandhiji’s iconic Dandi March in 1930 to protest against the British salt tax ?
Mahatma Gandhi Limited Edition-241 series (MGLE-241)
This pen costs Rs 11.39 lakh.
107. Who won the women’s singles title in the Yonex Czech international badminton championship?
Trupti Murgunde
Power systems switchgear and protection bits
1. What are the functions of protective relays
To detect the fault and initiate the operation of the circuit breaker to isolate
the defective element from the rest of the system, thereby protecting the system from damages consequent to the fault.
2. Give the consequences of short circuit.
Whenever a short-circuit occurs, the current flowing through the coil increases to an enormous value. If protective relays are present , a heavy current also flows through the relay coil, causing it to operate by closing its contacts.The trip circuit is then closed , the circuit breaker opens and the fault is isolated from the rest of the system. Also, a low voltage may be created which may damage systems connected to the supply.
3. Define protected zone.
Are those which are directly protected by a protective system such as relays,
fuses or switchgears.If a fault occurring in a zone can be immediately detected and or isolated by a protection scheme dedicated to that particular zone.
4. What are unit system and non unit system?
A unit protective system is one in which only faults occurring within its
protected zone are isolated.Faults occurring elsewhere in the system have no influence on the operation of a unit system.A non unit system is a protective system which is activated even when the faults are external to its protected zone.
5. What is primary protection?
Is the protection in which the fault occurring in a line will be cleared by its
own relay and circuit breaker.It serves as the first line of defence.
6. What is back up protection?
Is the second line of defence , which operates if the primary protection
fails to activate within a definite time delay.
7. Name the different kinds of over current relays.
Induction type non-directional over current relay,Induction type directional
over current relay & current differential relay.
8. Define energizing quantity.
It refers to the current or voltage which is used to activate the relay into
operation.
9. Define operating time of a relay.
It is defined as the time period extendind from the occurrence of the
fault through the relay detecting the fault to the operation of the relay.
10. Define resetting time of a relay.
It is defined as the time taken by the relay from the instant of isolating
the fault to the moment when the fault is removed and the relay can be reset.
11. What are over and under current relays?
Overcurrent relays are those that operate when the current in a line exceeds a
predetermined value. (eg: Induction type non-directional/directional overcurrent relay,differential overcurrent relay)whereas undercurrent relays are those which operate whenever the current in a circuit/line drops below a predetermined value.(eg: differential over-voltage relay)
12. Mention any two applications of differential relay.
Protection of generator & generator transformer unit; protection of large motors
and busbars .
13. What is biased differential bus zone reduction?
The biased beam relay is designed to respond to the differential current in terms
of its fractional relation to the current flowing through the protected zone. It is essentially an over-current balanced beam relay type with an additional restraining coil. The restraining coil produces a bias force in the opposite direction to the operating force.
14. What is the need of relay coordination?
The operation of a relay should be fast and selective, ie, it should isolate the fault
in the shortest possible time causing minimum disturbance to the system. Also, if a relay fails to operate, there should be sufficiently quick backup protection so that the rest of the system is protected. By coordinating relays, faults can always be isolated quickly without serious disturbance to the rest of the system.
15. Mention the short comings of Merz Price scheme of protection applied to a power transformer.
In a power transformer, currents in the primary and secondary are to be compared. As these two currents are usually different, the use of identical transformers will give differential current, and operate the relay under no-load condition. Also, there is usually a phase difference between the primary and secondary currents of three phase transformers. Even CT’s of proper turn-ratio are used, the differential current may flow through the relay under normal condition.
16. What are the various faults to which a turbo alternator is likely to be subjected?
Failure of steam supply; failure of speed; overcurrent; over voltage; unbalanced
loading; stator winding fault .
17. What is an under frequency relay?
An under frequency relay is one which operates when the frequency of the system (usually an alternator or transformer) falls below a certain value.
18. Define the term pilot with reference to power line protection.
Pilot wires refers to the wires that connect the CT’s placed at the ends of a power
transmission line as part of its protection scheme. The resistance of the pilot wires is usually less than 500 ohms.
19. Mention any two disadvantage of carrier current scheme for transmission line only.
The program time (ie, the time taken by the carrier to reach the other end-upto
.1% mile); the response time of band pass filter; capacitance phase-shift of the
transmission line .
20. What are the features of directional relay?
High speed operation; high sensitivity; ability to operate at low voltages; adequate short-time thermal ratio; burden must not be excessive.
21. What are the causes of over speed and how alternators are protected from it?
Sudden loss of all or major part of the load causes over-speeding in alternators.
Modern alternators are provided with mechanical centrifugal devices mounted on their driving shafts to trip the main valve of the prime mover when a dangerous over-speed occurs.
22. What are the main types of stator winding faults?
Fault between phase and ground; fault between phases and inter-turn fault
involving turns of the same phase winding.
23. Give the limitations of Merz Price protection.
Since neutral earthing resistances are often used to protect circuit from earth-fault currents, it becomes impossible to protect the whole of a star-connected alternator. If an earth-fault occurs near the neutral point, the voltage may be insufficient to operate the relay. Also it is extremely difficult to find two identical CT’s. In addition to this, there always an inherent phase difference between the primary and the secondary quantities and a possibility of current through the relay even when there is no fault.
24. What are the uses of Buchholz’s relay?
Bucholz relay is used to give an alarm in case of incipient( slow-developing)
faults in the transformer and to connect the transformer from the supply in the event of severe internal faults. It is usually used in oil immersion transformers with a rating over 750KVA.
25. What are the types of graded used in line of radial relay feeder?
Definite time relay and inverse-definite time relay.
26. What are the various faults that would affect an alternator?
(a) Stator faults
1, Phase to phase faults
2, Phase to earth faults
3, Inter turn faults
(b)
1, Earth faults
2, Fault between turns
3, Loss of excitation due to fuel failure
(c) 1, Over speed
2, Loss of drive
3, Vacuum failure resulting in condenser pressure rise, resulting in
shattering of the turbine low pressure casing
(d) 1, Fault on lines
2, Fault on busbars
27. Why neutral resistor is added between neutral and earth of an alternator?
In order to limit the flow of current through neutral and earth a resistor is
introduced between them.
28. What is the backup protection available for an alternator?
Overcurrent and earth fault protection is the backup protections.
29. What are faults associated with an alternator?
(a) External fault or through fault
(b) Internal fault
1, Short circuit in transformer winding and connection
2, Incipient or slow developing faults
30. What are the main safety devices available with transformer?
Oil level guage, sudden pressure delay, oil temperature indicator, winding
temperature indicator .
31. What are the limitations of Buchholz relay?
(a) Only fault below the oil level are detected.
(b) Mercury switch setting should be very accurate, otherwise even for
vibration, there can be a false operation.
(c) The relay is of slow operating type, which is unsatisfactory.
32. What are the problems arising in differential protection in power transformer and how are they overcome?
1. Difference in lengths of pilot wires on either sides of the relay. This is
overcome by connecting adjustable resistors to pilot wires to get equipotential
points on the pilot wires.
2. Difference in CT ratio error difference at high values of short circuit currents
that makes the relay to operate even for external or through faults. This is
overcome by introducing bias coil.
3. Tap changing alters the ratio of voltage and currents between HV and LV sides and the relay will sense this and act. Bias coil will solve this.
4. Magnetizing inrush current appears wherever a transformer is energized on its
primary side producing harmonics. No current will be seen by the secondary.
CT’s as there is no load in the circuit. This difference in current will actuate the
differential relay. A harmonic restraining unit is added to the relay which will
block it when the transformer is energized.
33. What is REF relay?
It is restricted earth fault relay. When the fault occurs very near to the neutral
point of the transformer, the voltage available to drive the earth circuit is very small,which may not be sufficient to activate the relay, unless the relay is set for a very low current. Hence the zone of protection in the winding of the transformer is restricted to cover only around 85%. Hence the relay is called REF relay.
34. What is over fluxing protection in transformer?
If the turns ratio of the transformer is more than 1:1, there will be higher core loss
and the capability of the transformer to withstand this is limited to a few minutes only.This phenomenon is called over fluxing.
35. Why busbar protection is needed?
(a) Fault level at busbar is high
(b) The stability of the system is affected by the faults in the bus zone.
(c) A fault in the bus bar causes interruption of supply to a large portion of the
system network.
36. What are the merits of carrier current protection?
Fast operation, auto re-closing possible, easy discrimination of simultaneous
faults .
37. What are the errors in CT?
(a) Ratio error
Percentage ratio error = [(Nominal ratio – Actual ratio)/Actual ratio] x 100
The value of transformation ratio is not equal to the turns ratio.
(b) Phase angle error:
Phase angle _ =180/_[(ImCos _-I1Sin _)/nIs]
38. What is field suppression?
When a fault occurs in an alternator winding even though the generator circuit
breaker is tripped, the fault continues to fed because EMF is induced in the generator itself. Hence the field circuit breaker is opened and stored energy in the field winding is discharged through another resistor. This method is known as field suppression.
39. What are the causes of bus zone faults?
_ Failure of support insulator resulting in earth fault
_ Flashover across support insulator during over voltage
_ Heavily polluted insulator causing flashover
_ Earthquake, mechanical damage etc.
40. What are the problems in bus zone differential protection?
_ Large number of circuits, different current levels for different circuits for
external faults.
_ Saturation of CT cores due to dc component and ac component in short
circuit currents. The saturation introduces ratio error.
_ Sectionalizing of the bus makes circuit complicated.
_ Setting of relays need a change with large load changes.
41. What is static relay?
It is a relay in which measurement or comparison of electrical quantities is made
in a static network which is designed to give an output signal when a threshold condition
is passed which operates a tripping device.
42. What is power swing?
During switching of lines or wrong synchronization surges of real and reactive
power flowing in transmission line causes severe oscillations in the voltage and current vectors. It is represented by curves originating in load regions and traveling towards relay characteristics.
43. What is a programmable relay?
A static relay may have one or more programmable units such as microprocessors
or microcomputers in its circuit.
44. What is CPMC?
It is combined protection, monitoring and control system incorporated in the static
system.
45. What are the advantages of static relay over electromagnetic relay?
o Low power consumption as low as 1mW
o No moving contacts; hence associated problems of arcing, contact bounce,
erosion, replacement of contacts
o No gravity effect on operation of static relays. Hence can be used in
vessels ie, ships, aircrafts etc.
o A single relay can perform several functions like over current, under
voltage, single phasing protection by incorporating respective functional
blocks. This is not possible in electromagnetic relays
o Static relay is compact
o Superior operating characteristics and accuracy
o Static relay can think , programmable operation is possible with static
relay
o Effect of vibration is nil, hence can be used in earthquake-prone areas
o Simplified testing and servicing. Can convert even non-electrical
quantities to electrical in conjunction with transducers.
46. What is resistance switching?
It is the method of connecting a resistance in parallel with the contact space(arc).
The resistance reduces the restriking voltage frequency and it diverts part of the arc current. It assists the circuit breaker in interrupting the magnetizing current and capacity current.
47. What do you mean by current chopping?
When interrupting low inductive currents such as magnetizing currents of the
transformer, shunt reactor, the rapid deionization of the contact space and blast effect may cause the current to be interrupted before the natural current zero. This phenomenon of interruption of the current before its natural zero is called current chopping.
48. What are the methods of capacitive switching?
Opening of single capacitor bank
Closing of one capacitor bank against another
49. What is an arc?
Arc is a phenomenon occurring when the two contacts of a circuit breaker
separate under heavy load or fault or short circuit condition.
50. Give the two methods of arc interruption?
_ High resistance interruption:-the arc resistance is increased by elongating, and
splitting the arc so that the arc is fully extinguished
_ Current zero method:-The arc is interrupted at current zero position that
occurs100 times a second in case of 50Hz power system frequency in ac.
51. What is restriking voltage?
It is the transient voltage appearing across the breaker contacts at the instant of arc
being extinguished.
52. What is meant by recovery voltage?
The power frequency rms voltage appearing across the breaker contacts after the arc is extinguished and transient oscillations die out is called recovery voltage.
53. What is RRRV?
It is the rate of rise of restriking voltage, expressed in volts per microsecond. It is
closely associated with natural frequency of oscillation.
54. What is circuit breaker?
It is a piece of equipment used to break a circuit automatically under fault
conditions. It breaks a circuit either manually or by remote control under normal
conditions and under fault conditions.
55. Write the classification of circuit breakers based on the medium used for arc
extinction?
_ Air break circuit breaker
_ Oil circuit breaker
_ Minimum oil circuit breaker
_ Air blast circuit breaker
_ SF6 circuit breaker
_ Vacuum circuit breaker
56. What is the main problem of the circuit breaker?
When the contacts of the breaker are separated, an arc is struck between them.
This arc delays the current interruption process and also generates enormous heat which may cause damage to the system or to the breaker itself. This is the main problem.
57. What are demerits of MOCB?
_ Short contact life
_ Frequent maintenance
_ Possibility of explosion
_ Larger arcing time for small currents
_ Prone to restricts
58. What are the advantages of oil as arc quenching medium?
It absorbs the arc energy to decompose the oil into gases, which have
excellent cooling properties
It acts as an insulator and permits smaller clearance between line conductors
and earthed components
59. What are the hazards imposed by oil when it is used as an arc quenching medium?
There is a risk of fire since it is inflammable. It may form an explosive mixture
with arc. So oil is preferred as an arc quenching medium.
60. What are the advantages of MOCB over a bulk oil circuit breaker?
It requires lesser quantity of oil
It requires smaller space
There is a reduced risk of fire
Maintenance problem are reduced
61. What are the disadvantages of MOCB over a bulk oil circuit breaker?
o The degree of carbonization is increased due to smaller quantity of oil
o There is difficulty of removing the gases from the contact space in time
o The dielectric strength of the oil deteriorates rapidly due to high degree of
carbonization.
62. What are the types of air blast circuit breaker?
_ Arial-blast type
_ Cross blast
_ Radial-blast
63. What are the advantages of air blast circuit breaker over oil circuit breaker?
o The risk of fire is diminished
o The arcing time is very small due to rapid buildup of dielectric strength
between contacts
o The arcing products are completely removed by the blast whereas oil
deteriorates with successive operations
64. What are the demerits of using oil as an arc quenching medium?
The air has relatively inferior arc quenching properties
The air blast circuit breakers are very sensitive to variations in the rate of rise
of restriking voltage
Maintenance is required for the compression plant which supplies the air blast
65. What is meant by electro negativity of SF6 gas?
SF6 has high affinity for electrons. When a free electron comes and collides with
a neutral gas molecule, the electron is absorbed by the neutral gas molecule and negative ion is formed. This is called as electro negativity of SF6 gas.
66. What are the characteristic of SF6 gas?
It has good dielectric strength and excellent arc quenching property. It is inert,
non-toxic, noninflammable and heavy. At atmospheric pressure, its dielectric strength is 2.5 times that of air. At three times atmospheric pressure, its dielectric strength is equal to that of the transformer oil.
67. Write the classifications of test conducted on circuit breakers.
_ Type test
_ Routine test
_ Reliability test
_ Commissioning test
68. What are the indirect methods of circuit breaker testing?
o Unit test
o Synthetic test
o Substitution testing
o Compensation testing
o Capacitance testing
69. What are the advantages of synthetic testing methods?
The breaker can be tested for desired transient recovery voltage and RRRV.
Both test current and test voltage can be independently varied. This gives
flexibility to the test
The method is simple
With this method a breaker capacity (MVA) of five time of that of the
capacity of the test plant can be tested.
70. How does the over voltage surge affect the power system?
The over voltage of the power system leads to insulation breakdown of the
equipments. It causes the line insulation to flash over and may also damage the nearby transformer, generators and the other equipment connected to the line.
71. What is pick up value?
It is the minimum current in the relay coil at which the relay starts to
operate.
72. Define target.
It is the indicator used for showing the operation of the relay.
73. Define reach.
It is the distance upto which the relay will cover for protection.
74. Define blocking.
It means preventing the relay from tripping due to its own
characteristics or due to additional relays.
75. Define a over current relay.
Relay which operates when the current ia a line exceeds a
predetermined value.
76. Define an under current relay?
Relays which operates whenever the current in a circuit drops below a
predetermined value.
77. Mention any 2 applications of differential relays.
Protection of generator and generator-transformer unit: protection of
large motors and bus bars
78.Mention the various tests carried out in a circuit breaker at HV labs.
Short circuit tests, Synthetic tests& direct tests.
78. Mention the advantages of field tests.
The circuit breaker is tested under actual conditions like those that occur in the
network. Special occasions like breaking of charging currents of long lines ,very short line faults ,interruption of small inductive currents etc… can be tested by direct testing only.
79. State the disadvantages of field tests.
The circuit breaker can be tested at only a given rated voltage and network
capacity. The necessity to interrupt the normal services and to test only at light load conditions.Extra inconvenience and expenses in installation of controlling and measuring equipment in the field.
80. Define composite testing of a circuit breaker.
In this method the breaker is first tested for its rated breaking capacity at a
reduced voltage and afterwards for rated voltage at a low current.This method does not give a proper estimate of the breaker performance.
81. State the various types of earthing.
Solid earthing, resistance earthing , reactance earthing , voltage transformer
earthing and zig-zag transformer earthing
82. What are arcing grounds?
The presence of inductive and capacitive currents in the isolated neutral system
leads to formation of arcs called as arcing grounds.
83. What is arc suppression coil?
A method of reactance grounding used to suppress the arc due to arcing
grounds.
84. State the significance of single line to ground fault.
In single line to ground fault all the sequence networks are connected
in series. All the sequence currents are equal and the fault current magnitude is three times its sequence currents.
85. What are symmetrical components?
It is a mathematical tool to resolve unbalanced components into balanced
components.
86. State the three sequence components.
Positive sequence components, negative sequence components and zero
sequence components.
87. Define positive sequence component.
-has 3 vectors equal in magnitude and displaced from each other by an angle
120 degrees and having the phase sequence as original vectors.
88. Define zero sequence component.
They has 3 vectors having equal magnitudes and displaced from each
other by an angle zero degees.
89. State the significance of double line fault.
It has no zero sequence component and the positive and negative sequence
networks are connected in parallel.
90. Define negative sequence component.
It has 3 vectors equal in magnitude and displaced from each other by an angle
120 degrees and has the phase sequence in opposite to its original phasors.
91. State the different types of faults.
Symmetrical faults and unsymmetrical faults and open conductor faults.
92. State the various types of unsymmetrical faults.
Line to ground ,line to line and double line to ground faults
93. Mention the withstanding current in our human body.
9mA
94. State the different types of circuit breakers.
Air ,oil,vacuum circuit breakers.
95. Define per unit value.
It is defined as the ratio of actual value to its base value.
96. Mention the inductance value of the peterson’s coil.
L=1/3c2
97. Define single line diagram.
Representation of various power system components in a single line is
defined as single line diagram.
98. Differentiate between a fuse and a circuit breaker.
Fuse is a low current interrupting device. It is a copper or an
aluminium wire.Circuit breaker is a high current interrupting device and it act as a switch under normal operating conditions.
99. How direct tests are conducted in circuit breakers?
Using a short circuit generator as the source.
Using the power utility system or network as the source.
100. What is dielectric test of a circuit breaker?
It consists of overvoltage withstand test of power frequency
lightning and impulse voltages.Testa are done for both internal and external insulation with switch in both open and closed conditions.
To detect the fault and initiate the operation of the circuit breaker to isolate
the defective element from the rest of the system, thereby protecting the system from damages consequent to the fault.
2. Give the consequences of short circuit.
Whenever a short-circuit occurs, the current flowing through the coil increases to an enormous value. If protective relays are present , a heavy current also flows through the relay coil, causing it to operate by closing its contacts.The trip circuit is then closed , the circuit breaker opens and the fault is isolated from the rest of the system. Also, a low voltage may be created which may damage systems connected to the supply.
3. Define protected zone.
Are those which are directly protected by a protective system such as relays,
fuses or switchgears.If a fault occurring in a zone can be immediately detected and or isolated by a protection scheme dedicated to that particular zone.
4. What are unit system and non unit system?
A unit protective system is one in which only faults occurring within its
protected zone are isolated.Faults occurring elsewhere in the system have no influence on the operation of a unit system.A non unit system is a protective system which is activated even when the faults are external to its protected zone.
5. What is primary protection?
Is the protection in which the fault occurring in a line will be cleared by its
own relay and circuit breaker.It serves as the first line of defence.
6. What is back up protection?
Is the second line of defence , which operates if the primary protection
fails to activate within a definite time delay.
7. Name the different kinds of over current relays.
Induction type non-directional over current relay,Induction type directional
over current relay & current differential relay.
8. Define energizing quantity.
It refers to the current or voltage which is used to activate the relay into
operation.
9. Define operating time of a relay.
It is defined as the time period extendind from the occurrence of the
fault through the relay detecting the fault to the operation of the relay.
10. Define resetting time of a relay.
It is defined as the time taken by the relay from the instant of isolating
the fault to the moment when the fault is removed and the relay can be reset.
11. What are over and under current relays?
Overcurrent relays are those that operate when the current in a line exceeds a
predetermined value. (eg: Induction type non-directional/directional overcurrent relay,differential overcurrent relay)whereas undercurrent relays are those which operate whenever the current in a circuit/line drops below a predetermined value.(eg: differential over-voltage relay)
12. Mention any two applications of differential relay.
Protection of generator & generator transformer unit; protection of large motors
and busbars .
13. What is biased differential bus zone reduction?
The biased beam relay is designed to respond to the differential current in terms
of its fractional relation to the current flowing through the protected zone. It is essentially an over-current balanced beam relay type with an additional restraining coil. The restraining coil produces a bias force in the opposite direction to the operating force.
14. What is the need of relay coordination?
The operation of a relay should be fast and selective, ie, it should isolate the fault
in the shortest possible time causing minimum disturbance to the system. Also, if a relay fails to operate, there should be sufficiently quick backup protection so that the rest of the system is protected. By coordinating relays, faults can always be isolated quickly without serious disturbance to the rest of the system.
15. Mention the short comings of Merz Price scheme of protection applied to a power transformer.
In a power transformer, currents in the primary and secondary are to be compared. As these two currents are usually different, the use of identical transformers will give differential current, and operate the relay under no-load condition. Also, there is usually a phase difference between the primary and secondary currents of three phase transformers. Even CT’s of proper turn-ratio are used, the differential current may flow through the relay under normal condition.
16. What are the various faults to which a turbo alternator is likely to be subjected?
Failure of steam supply; failure of speed; overcurrent; over voltage; unbalanced
loading; stator winding fault .
17. What is an under frequency relay?
An under frequency relay is one which operates when the frequency of the system (usually an alternator or transformer) falls below a certain value.
18. Define the term pilot with reference to power line protection.
Pilot wires refers to the wires that connect the CT’s placed at the ends of a power
transmission line as part of its protection scheme. The resistance of the pilot wires is usually less than 500 ohms.
19. Mention any two disadvantage of carrier current scheme for transmission line only.
The program time (ie, the time taken by the carrier to reach the other end-upto
.1% mile); the response time of band pass filter; capacitance phase-shift of the
transmission line .
20. What are the features of directional relay?
High speed operation; high sensitivity; ability to operate at low voltages; adequate short-time thermal ratio; burden must not be excessive.
21. What are the causes of over speed and how alternators are protected from it?
Sudden loss of all or major part of the load causes over-speeding in alternators.
Modern alternators are provided with mechanical centrifugal devices mounted on their driving shafts to trip the main valve of the prime mover when a dangerous over-speed occurs.
22. What are the main types of stator winding faults?
Fault between phase and ground; fault between phases and inter-turn fault
involving turns of the same phase winding.
23. Give the limitations of Merz Price protection.
Since neutral earthing resistances are often used to protect circuit from earth-fault currents, it becomes impossible to protect the whole of a star-connected alternator. If an earth-fault occurs near the neutral point, the voltage may be insufficient to operate the relay. Also it is extremely difficult to find two identical CT’s. In addition to this, there always an inherent phase difference between the primary and the secondary quantities and a possibility of current through the relay even when there is no fault.
24. What are the uses of Buchholz’s relay?
Bucholz relay is used to give an alarm in case of incipient( slow-developing)
faults in the transformer and to connect the transformer from the supply in the event of severe internal faults. It is usually used in oil immersion transformers with a rating over 750KVA.
25. What are the types of graded used in line of radial relay feeder?
Definite time relay and inverse-definite time relay.
26. What are the various faults that would affect an alternator?
(a) Stator faults
1, Phase to phase faults
2, Phase to earth faults
3, Inter turn faults
(b)
1, Earth faults
2, Fault between turns
3, Loss of excitation due to fuel failure
(c) 1, Over speed
2, Loss of drive
3, Vacuum failure resulting in condenser pressure rise, resulting in
shattering of the turbine low pressure casing
(d) 1, Fault on lines
2, Fault on busbars
27. Why neutral resistor is added between neutral and earth of an alternator?
In order to limit the flow of current through neutral and earth a resistor is
introduced between them.
28. What is the backup protection available for an alternator?
Overcurrent and earth fault protection is the backup protections.
29. What are faults associated with an alternator?
(a) External fault or through fault
(b) Internal fault
1, Short circuit in transformer winding and connection
2, Incipient or slow developing faults
30. What are the main safety devices available with transformer?
Oil level guage, sudden pressure delay, oil temperature indicator, winding
temperature indicator .
31. What are the limitations of Buchholz relay?
(a) Only fault below the oil level are detected.
(b) Mercury switch setting should be very accurate, otherwise even for
vibration, there can be a false operation.
(c) The relay is of slow operating type, which is unsatisfactory.
32. What are the problems arising in differential protection in power transformer and how are they overcome?
1. Difference in lengths of pilot wires on either sides of the relay. This is
overcome by connecting adjustable resistors to pilot wires to get equipotential
points on the pilot wires.
2. Difference in CT ratio error difference at high values of short circuit currents
that makes the relay to operate even for external or through faults. This is
overcome by introducing bias coil.
3. Tap changing alters the ratio of voltage and currents between HV and LV sides and the relay will sense this and act. Bias coil will solve this.
4. Magnetizing inrush current appears wherever a transformer is energized on its
primary side producing harmonics. No current will be seen by the secondary.
CT’s as there is no load in the circuit. This difference in current will actuate the
differential relay. A harmonic restraining unit is added to the relay which will
block it when the transformer is energized.
33. What is REF relay?
It is restricted earth fault relay. When the fault occurs very near to the neutral
point of the transformer, the voltage available to drive the earth circuit is very small,which may not be sufficient to activate the relay, unless the relay is set for a very low current. Hence the zone of protection in the winding of the transformer is restricted to cover only around 85%. Hence the relay is called REF relay.
34. What is over fluxing protection in transformer?
If the turns ratio of the transformer is more than 1:1, there will be higher core loss
and the capability of the transformer to withstand this is limited to a few minutes only.This phenomenon is called over fluxing.
35. Why busbar protection is needed?
(a) Fault level at busbar is high
(b) The stability of the system is affected by the faults in the bus zone.
(c) A fault in the bus bar causes interruption of supply to a large portion of the
system network.
36. What are the merits of carrier current protection?
Fast operation, auto re-closing possible, easy discrimination of simultaneous
faults .
37. What are the errors in CT?
(a) Ratio error
Percentage ratio error = [(Nominal ratio – Actual ratio)/Actual ratio] x 100
The value of transformation ratio is not equal to the turns ratio.
(b) Phase angle error:
Phase angle _ =180/_[(ImCos _-I1Sin _)/nIs]
38. What is field suppression?
When a fault occurs in an alternator winding even though the generator circuit
breaker is tripped, the fault continues to fed because EMF is induced in the generator itself. Hence the field circuit breaker is opened and stored energy in the field winding is discharged through another resistor. This method is known as field suppression.
39. What are the causes of bus zone faults?
_ Failure of support insulator resulting in earth fault
_ Flashover across support insulator during over voltage
_ Heavily polluted insulator causing flashover
_ Earthquake, mechanical damage etc.
40. What are the problems in bus zone differential protection?
_ Large number of circuits, different current levels for different circuits for
external faults.
_ Saturation of CT cores due to dc component and ac component in short
circuit currents. The saturation introduces ratio error.
_ Sectionalizing of the bus makes circuit complicated.
_ Setting of relays need a change with large load changes.
41. What is static relay?
It is a relay in which measurement or comparison of electrical quantities is made
in a static network which is designed to give an output signal when a threshold condition
is passed which operates a tripping device.
42. What is power swing?
During switching of lines or wrong synchronization surges of real and reactive
power flowing in transmission line causes severe oscillations in the voltage and current vectors. It is represented by curves originating in load regions and traveling towards relay characteristics.
43. What is a programmable relay?
A static relay may have one or more programmable units such as microprocessors
or microcomputers in its circuit.
44. What is CPMC?
It is combined protection, monitoring and control system incorporated in the static
system.
45. What are the advantages of static relay over electromagnetic relay?
o Low power consumption as low as 1mW
o No moving contacts; hence associated problems of arcing, contact bounce,
erosion, replacement of contacts
o No gravity effect on operation of static relays. Hence can be used in
vessels ie, ships, aircrafts etc.
o A single relay can perform several functions like over current, under
voltage, single phasing protection by incorporating respective functional
blocks. This is not possible in electromagnetic relays
o Static relay is compact
o Superior operating characteristics and accuracy
o Static relay can think , programmable operation is possible with static
relay
o Effect of vibration is nil, hence can be used in earthquake-prone areas
o Simplified testing and servicing. Can convert even non-electrical
quantities to electrical in conjunction with transducers.
46. What is resistance switching?
It is the method of connecting a resistance in parallel with the contact space(arc).
The resistance reduces the restriking voltage frequency and it diverts part of the arc current. It assists the circuit breaker in interrupting the magnetizing current and capacity current.
47. What do you mean by current chopping?
When interrupting low inductive currents such as magnetizing currents of the
transformer, shunt reactor, the rapid deionization of the contact space and blast effect may cause the current to be interrupted before the natural current zero. This phenomenon of interruption of the current before its natural zero is called current chopping.
48. What are the methods of capacitive switching?
Opening of single capacitor bank
Closing of one capacitor bank against another
49. What is an arc?
Arc is a phenomenon occurring when the two contacts of a circuit breaker
separate under heavy load or fault or short circuit condition.
50. Give the two methods of arc interruption?
_ High resistance interruption:-the arc resistance is increased by elongating, and
splitting the arc so that the arc is fully extinguished
_ Current zero method:-The arc is interrupted at current zero position that
occurs100 times a second in case of 50Hz power system frequency in ac.
51. What is restriking voltage?
It is the transient voltage appearing across the breaker contacts at the instant of arc
being extinguished.
52. What is meant by recovery voltage?
The power frequency rms voltage appearing across the breaker contacts after the arc is extinguished and transient oscillations die out is called recovery voltage.
53. What is RRRV?
It is the rate of rise of restriking voltage, expressed in volts per microsecond. It is
closely associated with natural frequency of oscillation.
54. What is circuit breaker?
It is a piece of equipment used to break a circuit automatically under fault
conditions. It breaks a circuit either manually or by remote control under normal
conditions and under fault conditions.
55. Write the classification of circuit breakers based on the medium used for arc
extinction?
_ Air break circuit breaker
_ Oil circuit breaker
_ Minimum oil circuit breaker
_ Air blast circuit breaker
_ SF6 circuit breaker
_ Vacuum circuit breaker
56. What is the main problem of the circuit breaker?
When the contacts of the breaker are separated, an arc is struck between them.
This arc delays the current interruption process and also generates enormous heat which may cause damage to the system or to the breaker itself. This is the main problem.
57. What are demerits of MOCB?
_ Short contact life
_ Frequent maintenance
_ Possibility of explosion
_ Larger arcing time for small currents
_ Prone to restricts
58. What are the advantages of oil as arc quenching medium?
It absorbs the arc energy to decompose the oil into gases, which have
excellent cooling properties
It acts as an insulator and permits smaller clearance between line conductors
and earthed components
59. What are the hazards imposed by oil when it is used as an arc quenching medium?
There is a risk of fire since it is inflammable. It may form an explosive mixture
with arc. So oil is preferred as an arc quenching medium.
60. What are the advantages of MOCB over a bulk oil circuit breaker?
It requires lesser quantity of oil
It requires smaller space
There is a reduced risk of fire
Maintenance problem are reduced
61. What are the disadvantages of MOCB over a bulk oil circuit breaker?
o The degree of carbonization is increased due to smaller quantity of oil
o There is difficulty of removing the gases from the contact space in time
o The dielectric strength of the oil deteriorates rapidly due to high degree of
carbonization.
62. What are the types of air blast circuit breaker?
_ Arial-blast type
_ Cross blast
_ Radial-blast
63. What are the advantages of air blast circuit breaker over oil circuit breaker?
o The risk of fire is diminished
o The arcing time is very small due to rapid buildup of dielectric strength
between contacts
o The arcing products are completely removed by the blast whereas oil
deteriorates with successive operations
64. What are the demerits of using oil as an arc quenching medium?
The air has relatively inferior arc quenching properties
The air blast circuit breakers are very sensitive to variations in the rate of rise
of restriking voltage
Maintenance is required for the compression plant which supplies the air blast
65. What is meant by electro negativity of SF6 gas?
SF6 has high affinity for electrons. When a free electron comes and collides with
a neutral gas molecule, the electron is absorbed by the neutral gas molecule and negative ion is formed. This is called as electro negativity of SF6 gas.
66. What are the characteristic of SF6 gas?
It has good dielectric strength and excellent arc quenching property. It is inert,
non-toxic, noninflammable and heavy. At atmospheric pressure, its dielectric strength is 2.5 times that of air. At three times atmospheric pressure, its dielectric strength is equal to that of the transformer oil.
67. Write the classifications of test conducted on circuit breakers.
_ Type test
_ Routine test
_ Reliability test
_ Commissioning test
68. What are the indirect methods of circuit breaker testing?
o Unit test
o Synthetic test
o Substitution testing
o Compensation testing
o Capacitance testing
69. What are the advantages of synthetic testing methods?
The breaker can be tested for desired transient recovery voltage and RRRV.
Both test current and test voltage can be independently varied. This gives
flexibility to the test
The method is simple
With this method a breaker capacity (MVA) of five time of that of the
capacity of the test plant can be tested.
70. How does the over voltage surge affect the power system?
The over voltage of the power system leads to insulation breakdown of the
equipments. It causes the line insulation to flash over and may also damage the nearby transformer, generators and the other equipment connected to the line.
71. What is pick up value?
It is the minimum current in the relay coil at which the relay starts to
operate.
72. Define target.
It is the indicator used for showing the operation of the relay.
73. Define reach.
It is the distance upto which the relay will cover for protection.
74. Define blocking.
It means preventing the relay from tripping due to its own
characteristics or due to additional relays.
75. Define a over current relay.
Relay which operates when the current ia a line exceeds a
predetermined value.
76. Define an under current relay?
Relays which operates whenever the current in a circuit drops below a
predetermined value.
77. Mention any 2 applications of differential relays.
Protection of generator and generator-transformer unit: protection of
large motors and bus bars
78.Mention the various tests carried out in a circuit breaker at HV labs.
Short circuit tests, Synthetic tests& direct tests.
78. Mention the advantages of field tests.
The circuit breaker is tested under actual conditions like those that occur in the
network. Special occasions like breaking of charging currents of long lines ,very short line faults ,interruption of small inductive currents etc… can be tested by direct testing only.
79. State the disadvantages of field tests.
The circuit breaker can be tested at only a given rated voltage and network
capacity. The necessity to interrupt the normal services and to test only at light load conditions.Extra inconvenience and expenses in installation of controlling and measuring equipment in the field.
80. Define composite testing of a circuit breaker.
In this method the breaker is first tested for its rated breaking capacity at a
reduced voltage and afterwards for rated voltage at a low current.This method does not give a proper estimate of the breaker performance.
81. State the various types of earthing.
Solid earthing, resistance earthing , reactance earthing , voltage transformer
earthing and zig-zag transformer earthing
82. What are arcing grounds?
The presence of inductive and capacitive currents in the isolated neutral system
leads to formation of arcs called as arcing grounds.
83. What is arc suppression coil?
A method of reactance grounding used to suppress the arc due to arcing
grounds.
84. State the significance of single line to ground fault.
In single line to ground fault all the sequence networks are connected
in series. All the sequence currents are equal and the fault current magnitude is three times its sequence currents.
85. What are symmetrical components?
It is a mathematical tool to resolve unbalanced components into balanced
components.
86. State the three sequence components.
Positive sequence components, negative sequence components and zero
sequence components.
87. Define positive sequence component.
-has 3 vectors equal in magnitude and displaced from each other by an angle
120 degrees and having the phase sequence as original vectors.
88. Define zero sequence component.
They has 3 vectors having equal magnitudes and displaced from each
other by an angle zero degees.
89. State the significance of double line fault.
It has no zero sequence component and the positive and negative sequence
networks are connected in parallel.
90. Define negative sequence component.
It has 3 vectors equal in magnitude and displaced from each other by an angle
120 degrees and has the phase sequence in opposite to its original phasors.
91. State the different types of faults.
Symmetrical faults and unsymmetrical faults and open conductor faults.
92. State the various types of unsymmetrical faults.
Line to ground ,line to line and double line to ground faults
93. Mention the withstanding current in our human body.
9mA
94. State the different types of circuit breakers.
Air ,oil,vacuum circuit breakers.
95. Define per unit value.
It is defined as the ratio of actual value to its base value.
96. Mention the inductance value of the peterson’s coil.
L=1/3c2
97. Define single line diagram.
Representation of various power system components in a single line is
defined as single line diagram.
98. Differentiate between a fuse and a circuit breaker.
Fuse is a low current interrupting device. It is a copper or an
aluminium wire.Circuit breaker is a high current interrupting device and it act as a switch under normal operating conditions.
99. How direct tests are conducted in circuit breakers?
Using a short circuit generator as the source.
Using the power utility system or network as the source.
100. What is dielectric test of a circuit breaker?
It consists of overvoltage withstand test of power frequency
lightning and impulse voltages.Testa are done for both internal and external insulation with switch in both open and closed conditions.
transmission lines and waveguide bits
http://www.niceindia.com/qbank/EC_1403_Microwave_Engineering.pdf
digital electronics bits n theory quest
Unit – 1
1. Define binary logic?
Binary logic consists of binary variables and logical operations. The variables are
designated by the alphabets such as A, B, C, x, y, z, etc., with each variable having only two distinct values: 1 and 0. There are three basic logic operations: AND, OR, and NOT.
The three basic logic gates are
AND gate
OR gate NOT gate
Logic gates are the basic elements that make up a digital system. The electronic gate
is a circuit that is able to operate on a number of binary inputs in order to perform a particular logical function.
Bipolar Unipolar
Saturated Non Saturated PMOS
NMOS
CMOS
RTL Schottky TTL
ECL DTL
The NAND and NOR gates are called as the universal gates. These gates are used to perform any type of logic application.
The Bipolar logic family is classified into
Saturated logic Unsaturated logic.The RTL, DTL, TTL, I2L, HTL logic comes under the saturated logic family.The Schottky TTL, and ECL logic comes under the unsaturated logic family.
FET is classified as
1. Junction Field Effect Transistor (JFET)
The bipolar logic family is classified as follows:
RTL- Resistor Transistor Logic
DTL- Diode Transistor logic
I2L- Integrated Injection Logic TTL- Transistor Transistor Logic ECL- Emitter Coupled Logic
Fan out
Power dissipation
Propagation Delay
Noise Margin
Fan In
Operating temperature,Power supply requirements
Fan out specifies the number of standard loads that the output of the gate can drive with out impairment of its normal operation.
Power dissipation is measure of power consumed by the gate when fully driven by all its inputs.
Propagation delay is the average transition delay time for the signal to propagate from input to output when the signals change in value. It is expressed in ns.
It is the maximum noise voltage added to an input signal of a digital circuit that does not cause an undesirable change in the circuit output. It is expressed in volts.
Fan in is the number of inputs connected to the gate without any degradation in the voltage level.
All the gates or semiconductor devices are temperature sensitive in nature. The
temperature in which the performance of the IC is effective is called as operating temperature. Operating temperature of the IC vary from 00 C to 700 c.
Some digital circuits operate in environments, which produce very high noise signals.
For operation in such surroundings there is available a type of DTL gate which possesses a high threshold to noise immunity. This type of gate is called HTL logic or High Threshold Logic.
1. Open collector output
If the channel is initially doped lightly with p-type impurity a conducting channel exists at zero gate voltage and the device is said to operate in depletion mode.
If the region beneath the gate is left initially uncharged the gate field must induce a
channel before current can flow. Thus the gate voltage enhances the channel current and such a device is said to operate in the enhancement mode.
1. The n- channel MOS conducts when its gate- to- source voltage is positive.
2. The p- channel MOS conducts when its gate- to- source voltage is negative
A schottky diode is formed by the combination of metal and semiconductor. The
presence of schottky diode between the base and the collector prevents the transistor from
going into saturation. The resulting transistor is called as schottky transistor.
The use of schottky transistor in TTL decreases the propagation delay without a
1.TTL (Std.TTL) 2.LTTL (Low Power TTL)
3.HTTL (High Speed TTL) 4.STTL (Schottky TTL)
Totem pole outputs cannot be connected together because such a connection might produce excessive current and may result in damage to the devices.
Adv: Easily compatible with other ICs
Low output impedance
Disadv: Wired output capability is possible only with tristate and open collector types Special circuits in Circuit layout and system design are required.
When noise voltages are within the limits of VNA(High State Noise Margin) and VNK for a particular logic family.
It is the oldest and standard CMOS family. The devices are not pin compatible or
When logic gates are connected together to produce a specified output for certain
specified combinations of input variables, with no storage involved, the resulting circuit is called combinational logic.
The problem definition
Determine the number of available input variables & required O/P variables.
Assigning letter symbols to I/O variables
Obtain simplified Boolean expression for each O/P.Obtain the logic diagram.
The logic circuit that performs the addition of two bits is a half adder. The circuit that performs the addition of three bits is a full adder.
A decoder is a multiple - input multiple output logic circuit that converts codedinputs into coded outputs where the input and output codes are different.
A decoder is a combinational circuit that converts binary information from n input lines to a maximum of 2n out puts lines.
An encoder has 2n input lines and n output lines. In encoder the output lines generate the binary code corresponding to the input value.
A priority encoder is an encoder circuit that includes the priority function. In priority
encoder, if 2 or more inputs are equal to 1 at the same time, the input having the highest priority will take precedence.
Multiplexer is a digital switch. If allows digital information from several sources to be routed onto a single output line.
. Read only memory . Programmable logic Array . Programmable Array Logic
A read only memory(ROM) is a device that includes both the decoder and the OR
gates within a single IC package. It consists of n input lines and m output lines. Each bit
combination of the input variables is called an address. Each bit combination that comes out
of the output lines is called a word. The number of distinct addresses possible with n input variables is 2n.
In a ROM, each bit combination of the input variable is called on address. Each bit combination that comes out of the output lines is called a word.
. Masked ROM.
. Programmable Read only Memory
. Erasable Programmable Read only memory.. Electrically Erasable Programmable Read only Memory.
PROM (Programmable Read Only Memory)
It allows user to store data or program. PROMs use the fuses with material
like nichrome and polycrystalline. The user can blow these fuses by passing
around 20 to 50 mA of current for the period 5 to 20µs.The blowing of fuses is
called programming of ROM. The PROMs are one time programmable. Once programmed, the information is stored permanent.
EPROM(Erasable Programmable Read Only Memory)
EPROM use MOS circuitry. They store 1’s and 0’s as a packet of charge in a
buried layer of the IC chip. We can erase the stored data in the EPROMs by
exposing the chip to ultraviolet light via its quartz window for 15 to 20
minutes. It is not possible to erase selective information. The chip can bereprogrammed.
EEPROM also use MOS circuitry. Data is stored as charge or no charge on an
insulated layer or an insulated floating gate in the device. EEPROM allows
selective erasing at the register level rather than erasing all the information
since the information can be changed by using electrical signals.
In some cases the number of don’t care conditions is excessive, it is more economical to use a second type of LSI component called a PLA. A PLA is similar to a ROM in concept;however it does not provide full decoding of the variables and does not generates all the minterms as in the ROM.
With a mask programmable PLA, the user must submit a PLA program table to the manufacturer.
PLA: Both AND and OR arrays are programmable and Complex
Costlier than PAL
PAL
AND arrays are programmable OR arrays are fixed Cheaper and Simpler
Programmable Logic Devices consist of a large array of AND gates and OR gates that can be programmed to achieve specific logic functions.
PLDs are classified as PROM(Programmable Read Only Memory), ProgrammableLogic Array(PLA), Programmable Array Logic (PAL), and Generic Array Logic(GAL)
PROM is Programmable Read Only Memory. It consists of a set of fixed AND gatesconnected to a decoder and a programmable OR array.
PLA is Programmable Logic Array(PLA). The PLA is a PLD that consists of aprogrammable AND array and a programmable OR array.
It is a PLD that was developed to overcome certain disadvantages of PLA, such as longer delays due to additional fusible links that result from using two programmable arrays and more circuit complexity.
The input variables to a PAL are buffered to prevent loading by the large number of AND gate inputs to which available or its complement can be connected.
PAL - Programmable Logic Array
10 - Ten inputs
1. And array is fixed and OR Both AND and OR arrays are
array is programmable. Programmable.
2. Cheaper and simple to use. Costliest and complex than
PROMS.
63. What are the classification of sequential circuits?
The sequential circuits are classified on the basis of timing of their signals into two
types. They are,
The basic unit for storage is flip flop. A flip-flop maintains its output state either at 1 or 0 until directed by an input signal to change its state.
There are various types of flip flops. Some of them are mentioned below they are,
RS flip-flop
SR flip-flop
D flip-flop
In D flip-flop during the occurrence of clock pulse if D=1, the output Q is set and if D=0, the output is reset.
• When K input is low and J input is high the Q output of flip-flop is
set.
• When K input is high and J input is low the Q output of flip-flop is
reset.
• When both the inputs K and J are low the output does not change
• When both the inputs K and J are high it is possible to set or reset the flip-flop (ie) the output toggle on the next positive clock edge.
T flip-flop is also known as Toggle flip-flop.
• When T=0 there is no change in the output.
• When T=1 the output switch to the complement state (ie) the outputtoggles.
change in the input. Due to this in the positive half of the clock pulse if both J and K are high then output toggles continuously. This condition is called ‘race around condition’.
The problem of race around condition can solved by edge triggering flip flop. The
term edge triggering means that the flip-flop changes state either at the positive edge or negative edge of the clock pulse and it is sensitive to its inputs only at this transition of the clock.
A master-slave flip-flop consists of two flip-flops where one circuit serves as a master and the other as a slave.
The time required to change the voltage level from 10% to 90% is known as rise time(tr).
The time required to change the voltage level from 90% to 10% is known as fall time(tf).
The phase shift between the rectangular clock waveforms is referred to as skew and the time delay between the two clock pulses is called clock skew.
The setup time is the minimum time required to maintain a constant voltage levels at
the excitation inputs of the flip-flop device prior to the triggering edge of the clock pulse in order for the levels to be reliably clocked into the flip flop. It is denoted as tsetup.
The hold time is the minimum time for which the voltage levels at the excitationinputs must remain constant after the triggering edge of the clock pulse in order for the levels to be reliably clocked into the flip flop. It is denoted as thold .
A propagation delay is the time required to change the output after the application of the input.
A register is a group of flip-flops flip-flop can store one bit information. So an n-bit register
has a group of n flip-flops and is capable of storing any binary information/number containing n-bits.
The binary information in a register can be moved from stage to stage within the
register or into or out of the register upon application of clock pulses. This type of bit
movement or shifting is essential for certain arithmetic and logic operations used in microprocessors. This gives rise to group of registers called shift registers.
There are five types. They are,
Serial In Serial Out Shift Register
Serial In Parallel Out Shift Register
Parallel In Serial Out Shift Register
Parallel In Parallel Out Shift Register ,,Bidirectional Shift Register
RS flip-flop
In RS flip-flop there are four possible transitions from the present state to the
next state. They are,
00 transition: This can happen either when R=S=0 or when R=1 and
S=0.
01 transition: This can happen only when S=1 and R=0.
10 transition: This can happen only when S=0 and R=1.
11 transition: This can happen either when S=1 and R=0 or S=0 and
In sequential circuits the output variables dependent not only on the present input variables but they also depend up on the past history of these input variables.
Combinational circuits Sequential circuits
Memory unit is not required Memory unity is required Parallel adder is a combinational circuit Serial adder is a sequential circuit
The information stored in the memory elements at any given time define.s the present state of the sequential circuit.
The present state and the external inputs determine the outputs and the next state ofthe sequential circuit.
In synchronous sequential circuits, signals can affect the memory elements only at
discrete instant of time.
88. Define Asynchronous sequential circuit?
In asynchronous sequential circuits change in input signals can affect memory element at any instant of time.
Synchronous sequential circuits Asynchronous sequential circuits.
Memory elements are clocked flip-flops Memory elements are either unlocked flip -
flops or time delay elements.Easier to design More difficult to design
waveform Assume initially Q = 1
Here the latch input has to be pulsed momentarily to cause a change in the latch output state, and the output will remain in that new state even after the input pulse is over.
In the JK latch, the output is feedback to the input, and therefore changes in the output
results change in the input. Due to this in the positive half of the clock pulse if J and K are
both high then output toggles continuously. This condition is known as race around condition.
Asynchronous counters Synchronous counters
In this type of counter flip-flops are
connected in such a way that output of 1st
flip-flop drives the clock for the next flipflop.
In this type there is no connection between
output of first flip-flop and clock input of
the next flip - flop
All the flip-flops are Not clocked
simultaneously
All the flip-flops are clocked simultaneously
MOD - 32 ripple counter f max (ripple) = 5 x 50 ns = 4 MHZ]
-input variables changes if the circuit is stable
In synchronous circuits-state assignments are made with the objective of circuit
reduction Asynchronous circuits-its objective is to avoid critical races
-two or more binary state variables change their value in response to the change in i/p variable
-final stable state depends on the order in which the state variable changes
-shared row state assignment
-construction of primitive flow table
-reduction of flow table
-state assignment is made
The merger graph is defined as follows. It contains the same number of vertices as the
state table contains states. A line drawn between the two state vertices indicates each compatible state pair. It two states are incompatible no connecting line is drawn.
A Set of compatibles is said to be closed if, for every compatible contained in the set,all its implied compatibles are also contained in the set. A closed set of compatibles, which contains all the states of M, is called a closed covering.
For the design of sequential counters we have to relate present states and next states.The table, which represents the relationship between present states and next states, is called state table.
The combination of level signals that appear at the inputs and the outputs of the delays define what is called the total state of the circuit.
1. Construction of a primitive flow table from the problem statement.
2. Primitive flow table is reduced by eliminating redundant states using the state reduction
3. State assignment is made
It is defined as a flow table which has exactly one stable state for each row in the
1. Fundamental mode circuits
asynchronous circuit.
In synchronous circuit, the state assignments are made with the objective of circuit
an input variable, race condition occurs in an asynchronous sequential circuit. In case of
unequal delays, a race condition may cause the state variables to change in an unpredictable manner.
If the final stable state that the circuit reaches does not depend on the order in which the state variable changes, the race condition is not harmful and it is called a non critical race.
If the final stable state depends on the order in which the state variable changes, the race condition is harmful and it is called a critical race.
A cycle occurs when an asynchronous circuit makes a transition through a series ofunstable states. If a cycle does not contain a stable state, the circuit will go from one unstable to stable to another, until the inputs are changed.
Fundamental mode circuit assumes that. The input variables change only when the circuit is stable. Only one input variable can change at a given time and inputs are levels and not pulses.
Pulse mode circuit assumes that the input variables are pulses instead of level. The width of the pulses is long enough for the circuit to respond to the input and the pulse width must not be so long that it is still present after the new state is reached.
The delay elements provide a short term memory for the sequential circuit. The present state and next state variables in asynchronous sequential circuits are called secondary variables.
A transition from one stable state to another occurs only in response to a change in the
input state. After a change in one input has occurred, no other change in any input occurs
until the circuit enters a stable state. Such a mode of operation is referred to as a fundamental mode.
Races can be avoided by making a proper binary assignment to the state variables.Here, the state variables are assigned with binary numbers in such a way that only one state variable can change at any one state variable can change at any one time when a state transition occurs. To accomplish this, it is necessary that states between which transitions occur be given adjacent assignments. Two binary are said to be adjacent if they differ in only one variable.
The one hot state assignment is another method for finding a race free state
assignment. In this method, only one variable is active or hot for each row in the original
flow table, ie, it requires one state variable for each row of the flow table. Additional row are introduced to provide single variable changes between internal state transitions.
1. Define binary logic?
Binary logic consists of binary variables and logical operations. The variables are
designated by the alphabets such as A, B, C, x, y, z, etc., with each variable having only two distinct values: 1 and 0. There are three basic logic operations: AND, OR, and NOT.
The three basic logic gates are
AND gate
OR gate NOT gate
Logic gates are the basic elements that make up a digital system. The electronic gate
is a circuit that is able to operate on a number of binary inputs in order to perform a particular logical function.
Bipolar Unipolar
Saturated Non Saturated PMOS
NMOS
CMOS
RTL Schottky TTL
ECL DTL
I I L ,TTL
The NAND and NOR gates are called as the universal gates. These gates are used to perform any type of logic application.
The Bipolar logic family is classified into
Saturated logic Unsaturated logic.The RTL, DTL, TTL, I2L, HTL logic comes under the saturated logic family.The Schottky TTL, and ECL logic comes under the unsaturated logic family.
FET is classified as
1. Junction Field Effect Transistor (JFET)
2. Metal oxide semiconductor family (MOS).
The bipolar logic family is classified as follows:
RTL- Resistor Transistor Logic
DTL- Diode Transistor logic
I2L- Integrated Injection Logic TTL- Transistor Transistor Logic ECL- Emitter Coupled Logic
Fan out
Power dissipation
Propagation Delay
Noise Margin
Fan In
Operating temperature,Power supply requirements
Fan out specifies the number of standard loads that the output of the gate can drive with out impairment of its normal operation.
Power dissipation is measure of power consumed by the gate when fully driven by all its inputs.
Propagation delay is the average transition delay time for the signal to propagate from input to output when the signals change in value. It is expressed in ns.
It is the maximum noise voltage added to an input signal of a digital circuit that does not cause an undesirable change in the circuit output. It is expressed in volts.
Fan in is the number of inputs connected to the gate without any degradation in the voltage level.
All the gates or semiconductor devices are temperature sensitive in nature. The
temperature in which the performance of the IC is effective is called as operating temperature. Operating temperature of the IC vary from 00 C to 700 c.
Some digital circuits operate in environments, which produce very high noise signals.
For operation in such surroundings there is available a type of DTL gate which possesses a high threshold to noise immunity. This type of gate is called HTL logic or High Threshold Logic.
1. Open collector output
2. Totem-Pole Output
3. Tri-state output.
If the channel is initially doped lightly with p-type impurity a conducting channel exists at zero gate voltage and the device is said to operate in depletion mode.
If the region beneath the gate is left initially uncharged the gate field must induce a
channel before current can flow. Thus the gate voltage enhances the channel current and such a device is said to operate in the enhancement mode.
1. The n- channel MOS conducts when its gate- to- source voltage is positive.
2. The p- channel MOS conducts when its gate- to- source voltage is negative
3. Either type of device is turned of if its gate- to- source voltage is zero.
A schottky diode is formed by the combination of metal and semiconductor. The
presence of schottky diode between the base and the collector prevents the transistor from
going into saturation. The resulting transistor is called as schottky transistor.
The use of schottky transistor in TTL decreases the propagation delay without a
sacrifice of power dissipation.
1.TTL (Std.TTL) 2.LTTL (Low Power TTL)
3.HTTL (High Speed TTL) 4.STTL (Schottky TTL)
5.LSTTL (Low power Schottky TTL)
Totem pole outputs cannot be connected together because such a connection might produce excessive current and may result in damage to the devices.
Adv: Easily compatible with other ICs
Low output impedance
Disadv: Wired output capability is possible only with tristate and open collector types Special circuits in Circuit layout and system design are required.
When noise voltages are within the limits of VNA(High State Noise Margin) and VNK for a particular logic family.
It is the oldest and standard CMOS family. The devices are not pin compatible or
electrically compatible with any TTL Series.
Unit – II
When logic gates are connected together to produce a specified output for certain
specified combinations of input variables, with no storage involved, the resulting circuit is called combinational logic.
The problem definition
Determine the number of available input variables & required O/P variables.
Assigning letter symbols to I/O variables
Obtain simplified Boolean expression for each O/P.Obtain the logic diagram.
The logic circuit that performs the addition of two bits is a half adder. The circuit that performs the addition of three bits is a full adder.
A decoder is a multiple - input multiple output logic circuit that converts codedinputs into coded outputs where the input and output codes are different.
A decoder is a combinational circuit that converts binary information from n input lines to a maximum of 2n out puts lines.
An encoder has 2n input lines and n output lines. In encoder the output lines generate the binary code corresponding to the input value.
A priority encoder is an encoder circuit that includes the priority function. In priority
encoder, if 2 or more inputs are equal to 1 at the same time, the input having the highest priority will take precedence.
Multiplexer is a digital switch. If allows digital information from several sources to be routed onto a single output line.
A comparator is a special combinational circuit designed primarily to compare the relative magnitude of two binary numbers.
. Read only memory . Programmable logic Array . Programmable Array Logic
A read only memory(ROM) is a device that includes both the decoder and the OR
gates within a single IC package. It consists of n input lines and m output lines. Each bit
combination of the input variables is called an address. Each bit combination that comes out
of the output lines is called a word. The number of distinct addresses possible with n input variables is 2n.
In a ROM, each bit combination of the input variable is called on address. Each bit combination that comes out of the output lines is called a word.
. Masked ROM.
. Programmable Read only Memory
. Erasable Programmable Read only memory.. Electrically Erasable Programmable Read only Memory.
41. What is programmable logic array? How it differs from ROM?
In some cases the number of don’t care conditions is excessive, it is more economical to use a second type of LSI component called a PLA. A PLA is similar to a ROM in concept;however it does not provide full decoding of the variables and does not generates all the minterms as in the ROM.
42. Which gate is equal to AND-invert Gate?
NAND gate.
NOR gate.
NAND gate
NOR gate
PROM (Programmable Read Only Memory)
It allows user to store data or program. PROMs use the fuses with material
like nichrome and polycrystalline. The user can blow these fuses by passing
around 20 to 50 mA of current for the period 5 to 20µs.The blowing of fuses is
called programming of ROM. The PROMs are one time programmable. Once programmed, the information is stored permanent.
EPROM(Erasable Programmable Read Only Memory)
EPROM use MOS circuitry. They store 1’s and 0’s as a packet of charge in a
buried layer of the IC chip. We can erase the stored data in the EPROMs by
exposing the chip to ultraviolet light via its quartz window for 15 to 20
minutes. It is not possible to erase selective information. The chip can bereprogrammed.
48. Explain EEPROM.
EEPROM also use MOS circuitry. Data is stored as charge or no charge on an
insulated layer or an insulated floating gate in the device. EEPROM allows
selective erasing at the register level rather than erasing all the information
since the information can be changed by using electrical signals.
49. What is RAM?
Random Access Memory. Read and write operations can be carried out.
In some cases the number of don’t care conditions is excessive, it is more economical to use a second type of LSI component called a PLA. A PLA is similar to a ROM in concept;however it does not provide full decoding of the variables and does not generates all the minterms as in the ROM.
With a mask programmable PLA, the user must submit a PLA program table to the manufacturer.
52. What is field programmable logic array?
PLA: Both AND and OR arrays are programmable and Complex
Costlier than PAL
PAL
AND arrays are programmable OR arrays are fixed Cheaper and Simpler
Programmable Logic Devices consist of a large array of AND gates and OR gates that can be programmed to achieve specific logic functions.
PLDs are classified as PROM(Programmable Read Only Memory), ProgrammableLogic Array(PLA), Programmable Array Logic (PAL), and Generic Array Logic(GAL)
PROM is Programmable Read Only Memory. It consists of a set of fixed AND gatesconnected to a decoder and a programmable OR array.
PLA is Programmable Logic Array(PLA). The PLA is a PLD that consists of aprogrammable AND array and a programmable OR array.
PAL is Programmable Array Logic. PAL consists of a programmable AND array and a fixed OR array with output logic.
It is a PLD that was developed to overcome certain disadvantages of PLA, such as longer delays due to additional fusible links that result from using two programmable arrays and more circuit complexity.
The input variables to a PAL are buffered to prevent loading by the large number of AND gate inputs to which available or its complement can be connected.
PAL - Programmable Logic Array
10 - Ten inputs
L - Active LOW Ouput
8 - Eight Outputs
62.Give the comparison between PROM and PLA.
1. And array is fixed and OR Both AND and OR arrays are
array is programmable. Programmable.
2. Cheaper and simple to use. Costliest and complex than
PROMS.
63. What are the classification of sequential circuits?
The sequential circuits are classified on the basis of timing of their signals into two
types. They are,
1)Synchronous sequential circuit.
2)Asynchronous sequential circuit.
The basic unit for storage is flip flop. A flip-flop maintains its output state either at 1 or 0 until directed by an input signal to change its state.
There are various types of flip flops. Some of them are mentioned below they are,
RS flip-flop
SR flip-flop
D flip-flop
JK flip-flop
T flip-flop
In D flip-flop during the occurrence of clock pulse if D=1, the output Q is set and if D=0, the output is reset.
• When K input is low and J input is high the Q output of flip-flop is
set.
• When K input is high and J input is low the Q output of flip-flop is
reset.
• When both the inputs K and J are low the output does not change
• When both the inputs K and J are high it is possible to set or reset the flip-flop (ie) the output toggle on the next positive clock edge.
T flip-flop is also known as Toggle flip-flop.
• When T=0 there is no change in the output.
• When T=1 the output switch to the complement state (ie) the outputtoggles.
69. Define race around condition.
change in the input. Due to this in the positive half of the clock pulse if both J and K are high then output toggles continuously. This condition is called ‘race around condition’.
The problem of race around condition can solved by edge triggering flip flop. The
term edge triggering means that the flip-flop changes state either at the positive edge or negative edge of the clock pulse and it is sensitive to its inputs only at this transition of the clock.
A master-slave flip-flop consists of two flip-flops where one circuit serves as a master and the other as a slave.
The time required to change the voltage level from 10% to 90% is known as rise time(tr).
The time required to change the voltage level from 90% to 10% is known as fall time(tf).
The phase shift between the rectangular clock waveforms is referred to as skew and the time delay between the two clock pulses is called clock skew.
The setup time is the minimum time required to maintain a constant voltage levels at
the excitation inputs of the flip-flop device prior to the triggering edge of the clock pulse in order for the levels to be reliably clocked into the flip flop. It is denoted as tsetup.
The hold time is the minimum time for which the voltage levels at the excitationinputs must remain constant after the triggering edge of the clock pulse in order for the levels to be reliably clocked into the flip flop. It is denoted as thold .
A propagation delay is the time required to change the output after the application of the input.
A register is a group of flip-flops flip-flop can store one bit information. So an n-bit register
has a group of n flip-flops and is capable of storing any binary information/number containing n-bits.
The binary information in a register can be moved from stage to stage within the
register or into or out of the register upon application of clock pulses. This type of bit
movement or shifting is essential for certain arithmetic and logic operations used in microprocessors. This gives rise to group of registers called shift registers.
There are five types. They are,
Serial In Serial Out Shift Register
Serial In Parallel Out Shift Register
Parallel In Serial Out Shift Register
Parallel In Parallel Out Shift Register ,,Bidirectional Shift Register
RS flip-flop
In RS flip-flop there are four possible transitions from the present state to the
next state. They are,
00 transition: This can happen either when R=S=0 or when R=1 and
S=0.
01 transition: This can happen only when S=1 and R=0.
10 transition: This can happen only when S=0 and R=1.
11 transition: This can happen either when S=1 and R=0 or S=0 and
R=0.
In sequential circuits the output variables dependent not only on the present input variables but they also depend up on the past history of these input variables.
Combinational circuits Sequential circuits
Memory unit is not required Memory unity is required Parallel adder is a combinational circuit Serial adder is a sequential circuit
The information stored in the memory elements at any given time define.s the present state of the sequential circuit.
The present state and the external inputs determine the outputs and the next state ofthe sequential circuit.
86. State the types of sequential circuits?
2. Asynchronous sequential circuits
In synchronous sequential circuits, signals can affect the memory elements only at
discrete instant of time.
88. Define Asynchronous sequential circuit?
In asynchronous sequential circuits change in input signals can affect memory element at any instant of time.
Synchronous sequential circuits Asynchronous sequential circuits.
Memory elements are clocked flip-flops Memory elements are either unlocked flip -
flops or time delay elements.Easier to design More difficult to design
waveform Assume initially Q = 1
Here the latch input has to be pulsed momentarily to cause a change in the latch output state, and the output will remain in that new state even after the input pulse is over.
In the JK latch, the output is feedback to the input, and therefore changes in the output
results change in the input. Due to this in the positive half of the clock pulse if J and K are
both high then output toggles continuously. This condition is known as race around condition.
Asynchronous counters Synchronous counters
In this type of counter flip-flops are
connected in such a way that output of 1st
flip-flop drives the clock for the next flipflop.
In this type there is no connection between
output of first flip-flop and clock input of
the next flip - flop
All the flip-flops are Not clocked
simultaneously
All the flip-flops are clocked simultaneously
MOD - 32 ripple counter f max (ripple) = 5 x 50 ns = 4 MHZ]
-present state variables in asynchronous sequential circuits
-next state variables in asynchronous sequential circuits
-input variables changes if the circuit is stable
-inputs are levels, not pulses
-only one input can change at a given time
97. What are pulse mode circuit?
-width of pulses are long for circuit to respond to the input
-pulse width must not be so long that it is still present after the new state is reached
In synchronous circuits-state assignments are made with the objective of circuit
reduction Asynchronous circuits-its objective is to avoid critical races
-two or more binary state variables change their value in response to the change in i/p variable
-final stable state does not depend on the order in which the state variable changes
-race condition is not harmful
-final stable state depends on the order in which the state variable changes
-race condition is harmful
-asynchronous circuit makes a transition through a series of unstable state
-shared row state assignment
-one hot state assignment
-construction of primitive flow table
-reduction of flow table
-state assignment is made
-realization of primitive flow table
-unwanted switching transients
-output goes momentarily 0 when it should remain at 1
-output goes momentarily 1 when it should remain at 0
-output changes 3 or more times when it changes from 1 to 0 or 0 to 1
-unequal delays along 2 or more path from same input
-state table of an synchronous sequential network
-one stable state per row
Output depends on the given input. It has no storage element.
The merger graph is defined as follows. It contains the same number of vertices as the
state table contains states. A line drawn between the two state vertices indicates each compatible state pair. It two states are incompatible no connecting line is drawn.
A Set of compatibles is said to be closed if, for every compatible contained in the set,all its implied compatibles are also contained in the set. A closed set of compatibles, which contains all the states of M, is called a closed covering.
For the design of sequential counters we have to relate present states and next states.The table, which represents the relationship between present states and next states, is called state table.
The combination of level signals that appear at the inputs and the outputs of the delays define what is called the total state of the circuit.
1. Construction of a primitive flow table from the problem statement.
2. Primitive flow table is reduced by eliminating redundant states using the state reduction
3. State assignment is made
4. The primitive flow table is realized using appropriate logic elements.
It is defined as a flow table which has exactly one stable state for each row in the
table. The design process begins with the construction of primitive flow table.
1. Fundamental mode circuits
2. Pulse mode circuits
asynchronous circuit.
In synchronous circuit, the state assignments are made with the objective of circuit
reduction. In asynchronous circuits, the objective of state assignment is to avoid critical races.
121.What are races?
an input variable, race condition occurs in an asynchronous sequential circuit. In case of
unequal delays, a race condition may cause the state variables to change in an unpredictable manner.
If the final stable state that the circuit reaches does not depend on the order in which the state variable changes, the race condition is not harmful and it is called a non critical race.
If the final stable state depends on the order in which the state variable changes, the race condition is harmful and it is called a critical race.
A cycle occurs when an asynchronous circuit makes a transition through a series ofunstable states. If a cycle does not contain a stable state, the circuit will go from one unstable to stable to another, until the inputs are changed.
Fundamental mode circuit assumes that. The input variables change only when the circuit is stable. Only one input variable can change at a given time and inputs are levels and not pulses.
Pulse mode circuit assumes that the input variables are pulses instead of level. The width of the pulses is long enough for the circuit to respond to the input and the pulse width must not be so long that it is still present after the new state is reached.
The delay elements provide a short term memory for the sequential circuit. The present state and next state variables in asynchronous sequential circuits are called secondary variables.
128. Define flow table in asynchronous sequential circuit.
In asynchronous sequential circuit state table is known as flow table because of the behaviour of the asynchronous sequential circuit. The stage changes occur in independent of a clock, based on the logic propagation delay, and cause the states to .flow. from one to another.
129. A pulse mode asynchronous machine has two inputs. If produces an output whenever two consecutive pulses occur on one input line only. The output remains at 1 until a pulse has occurred on the other input line. Write down the state table for the machine.
A transition from one stable state to another occurs only in response to a change in the
input state. After a change in one input has occurred, no other change in any input occurs
until the circuit enters a stable state. Such a mode of operation is referred to as a fundamental mode.
Races can be avoided by making a proper binary assignment to the state variables.Here, the state variables are assigned with binary numbers in such a way that only one state variable can change at any one state variable can change at any one time when a state transition occurs. To accomplish this, it is necessary that states between which transitions occur be given adjacent assignments. Two binary are said to be adjacent if they differ in only one variable.
The one hot state assignment is another method for finding a race free state
assignment. In this method, only one variable is active or hot for each row in the original
flow table, ie, it requires one state variable for each row of the flow table. Additional row are introduced to provide single variable changes between internal state transitions.
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