ELECTRICAL ENGINEERING MPORTANT QUESTION AND ANSWERS FOR XAMS N INTERVIEWS

Question: What will happen when power factor is leading in distribution of power?
Ans: If there is high power factor, i.e., if the power factor is close to one:
1. Losses in form of heat will be reduced
2. Cable becomes less bulky and easy to carry, and very cheap to afford, &
3. It also reduces over heating of transformer

Question: What is the one main difference between UPS & inverter and electrical engineering & electronics engineering?
Ans: Uninterrupted power supply is mainly used for short time. Means according to ups VA it gives backup. UPS is also two types: online and offline. An online ups having high volt and amp for long time backup with high dc voltage. But ups start with 12v dc with 7 amps. But inverter is start with 12v, 24, dc to 36v dc and 120amp to 180amp battery with long time backup.

Question: What is ACSR cable and where we use it?
Ans: ACSR means Aluminium conductor steel reinforced, this conductor is used in transmission & distribution.

Question: What is the principle of motor?
Ans: Whenever a current carrying conductor is placed in an magnetic field it produce turning or twisting movement is called as torque

Question: What is meant by armature reaction?
Ans: The effect of armature flu to main flux is called armature reaction. The armature flux may support main flux or opposes main flux.

Question: Why Human bodies feel Electric shock?? In an Electric train during running, we don't feel any Shock. Why?
Ans: Unfortunately our body is a pretty good conductor of electricity, The golden rule is Current takes the lowest resistant path if you have insulation to our feet as the circuit is not complete (wearing rubber footwear which doing some repairs is advisable as our footwear is a high resistance path not much current flows through our body).The electric train is well insulated from its electrical system.

Question: Which motor has high Starting Torque and Staring current DC motor, Induction motor or Synchronous motor?
Ans: DC Series motor has high starting torque. We can not start the Induction motor and Synchronous motors on load, but can not start the DC series motor without load

Question: What is vacuum circuit breaker? Define with cause and where be use it Device?
Ans: A breaker is normally used to break a circuit. While breaking the circuit, the contact terminals will be separated. At the time of separation an air gap is formed in between the terminals. Due to existing current flow the air in the gap is ionized and results in the arc. Various mediums are used to quench this arc in respective CB's. But in VCB the medium is vacuum gas. Since the air in the CB is having vacuum pressure the arc formation is interrupted. VCB's can be used up to 11kv.

Question: Why when birds sit on transmission lines or current wires don't get shock?
Ans: It?s true that if birds touch the single one line (phase or neutral) they don't get electrical shock... if birds touch 2 lines than the circuit is closed and they get electrical shock. so if a human touch single one line (phase) then he doesn't get shock if he is in the air (not touching - standing on the ground if he is standing on the ground then touching the line (phase) he will get a shock because the ground on what we standing is like line (ground bed - like neutral) and in the most of electric lines the neutral is grounded. so that means that human who touch the line closes the circuit between phase and neutral.

Question: What happens if we give 220 volts dc supply to a bulb or tube light?
Ans: Bulbs [devices] for AC are designed to operate such that it offers high impedance to AC supply. Normally they have low resistance. When DC supply is applied, due to low resistance, the current through lamp would be so high that it may damage the bulb element.

Question: What are the advantages of speed control using thyristor?
Ans: Advantages:
1. Fast Switching Characteristics than Mosfet, BJT, IGBT
2. Low cost
3. Higher Accurate.

Question: How tube light circuit is connected and how it works?
Ans: A choke is connected in one end of the tube light and a starter is in series with the circuit. When supply is provided, the starter will interrupt the supply cycle of AC. Due to the sudden change of supply the chock will generate around 1000volts. This volt will capable of to break the electrons inside the tube to make electron flow. Once the current passes through the tube the starter circuit will be out of part. Now there is no change of supply causes choke voltage normalized and act as minimize the current.

Question: Why link is provided in neutral of an ac circuit and fuse in phase of ac circuit?
Ans: Link is provided at a Neutral common point in the circuit from which various connections are taken for the individual control circuit and so it is given in a link form to withstand high Amps. But in the case of Fuse in the Phase of AC circuit it is designed such that the fuse rating is calculated for the particular circuit (i.e. load) only. So if any malfunction happens the fuse connected in the particular control circuit alone will blow off.

Question: What is MARX CIRCUIT?
Ans: It is used with generators for charging a number of capacitor in parallel and discharging them in series. It is used when voltage required for testing is higher than the available.

Question: What is "pu" in electrical engineering?
Ans: ?pu? stands for per unit and this will be used in power system single line diagram there it is like a huge electrical circuit with no of components (generators, transformers, loads) with different ratings (in MVA and KV). To bring all the ratings into common platform we use pu concept in which, in general largest MVA and KV ratings of the component is considered as base values, then all other component ratings will get back into this basis. Those values are called as pu values. (pu = actual value/base value).

Question: What is electric traction?
Ans: Traction means using the electric power for traction system i.e. for railways, trams; trolleys etc. electric traction means use of the electricity for all these. Now a day, magnetic traction is also used for bullet trains. Basically dc motors are used for electric traction systems.

Question: Describe the operation carried out in thermal power station.
Ans: The water is obtained in the boiler and the coal is burnt so that steam is obtained this steam is allowed to hit the turbine; the turbine which is coupled with the generator generates the electricity

Electrical Engineering Interview Questions Question: What are the advantages of speed control using thyristor?
Ans: Advantages:
1. Fast Switching Characteristics than Mosfet, BJT, IGBT
2. Low cost
3. Higher Accurate. TOP Question: How tube light circuit is connected and how it works?
Ans: A choke is connected in one end of the tube light and a starter is in series with the circuit. When supply is provided, the starter will interrupt the supply cycle of AC. Due to the sudden change of supply the chock will generate around 1000volts. This volt will capable of to break the electrons inside the tube to make electron flow. Once the current passes through the tube the starter circuit will be out of part. Now there is no change of supply causes choke voltage normalized and act as minimize the current.

Question: Why link is provided in neutral of an ac circuit and fuse in phase of ac circuit?
Ans: Link is provided at a Neutral common point in the circuit from which various connections are taken for the individual control circuit and so it is given in a link form to withstand high Amps. But in the case of Fuse in the Phase of AC circuit it is designed such that the fuse rating is calculated for the particular circuit (i.e. load) only. So if any malfunction happens the fuse connected in the particular control circuit alone will blow off.


Question: How can you start-up the 40w tube light with 230v AC/DC without using any choke/Coil?
Ans: It's possible by means of Electronic choke. Otherwise it's not possible to ionize the particles in tube.

Question: Which type of A.C motor is used in the fans (ceiling fan, exhaust fan, padestal fan, bracket fan etc) which are found in the houses?
Ans: It is Single Phase Induction motor which mostly squirrel cage rotor and are capacitor start capacitor run.

Question: Why syn. generators r used for the production of electricity?
Ans: Synchronous machines have capability to work on different power factor (or say different imaginary power varying the field emf. Hence, synchronous generators are used for the production of electricity.

Question: Give two basic speed control scheme of DC shunt motor?
Ans: 1. By using flux control method: in this method a rheostat is connected across the field winding to control the field current. So by changing the current the flux produced by the field winding can be changed, and since speed is inversely proportional to flux speed can be controlled
2. Armature control method: in this method a rheostat is connected across armature wedge. By varying the resistance the value of resistive drop (IaRa)can be varied, and since speed is directly proportional to Eb-IaRa the speed can be controlled

Question: What is the significance of vector grouping in Power Transformers?
Ans: Every power transformer has a vector group listed by its manufacturer. Fundamentally it tells you the information about how the windings are connected (delta or wye) and the phase difference between the current and voltage. E.g. DYN11 means Delta primary, Wye Secondary and the current is at 11 o clock referred to the voltage.

Question: Give two basic speed control scheme of DC shunt motor?
Ans: 1. By using flux control method: in this method a rheostat is connected across the field winding to control the field current. So by changing the current the flux produced by the field winding can be changed, and since speed is inversely proportional to flux speed can be controlled.
2. Armature control method: in this method a rheostat is connected across armature winding by varying the resistance the value of resistive drop (IaRa) can be varied, and since speed is directly proportional to Eb-IaRa the speed can be controlled.

Question: What is meant by armature reaction?
Ans: The effect of armature flu to main flux is called armature reaction. The armature flux may support main flux or opposes main flux.

Question: What is 2 phase motor?
Ans: A two phase motor is a motor with the starting winding and the running winding have a phase split e.g.; ac servo motor where the auxiliary winding and the control winding have a phase split of 90 degree.

Question: What is the Polarization index value? (pi value)and simple definition of polarization index?
Ans: It?s ratio between insulation resistance (IR) i.e. meggar value for 10min to insulation resistance for 1 min. It ranges from 5-7 for new motors & normally for motor to be in good condition it should be Greater than 2.5.

Question: Advantages of vvvf drive over non-vvvf drives for EOT cranes.
Ans: 1. Smooth start and stop.
2. No jerking of load.
3. Exact positioning.
4. Better protection for motor.
5. high/low speed selection.
6. Reliability of break shoe.
7. Programmable break control.
8. Easy circuitry.
9. Reduction in controls.
10. Increases motor life.