ELECTRICAL INTERVIEW QUESTION
electrical interview question with answer;
1)Why star delta starter is used to start induction motor?
Star delta starter is preferred with induction motor due to following reasons:
• It reduce 3-4 time starting voltage,starting current and also torque.
2)State the difference between generator and alternator?
Generator and alternator are two devices, which converts mechanical energy into electrical energy. Both have the same principle of electromagnetic induction, the only difference is that their construction.
Alternator:ac to ac conversion.
Generator:dc to ac conversion
3)Why AC systems is better DC systems?
Due to following reasons, AC systems are preferred over DC systems:
a. It is easy to maintain and change the voltage of AC electricity for transmission and distribution.
b. Plant cost for AC transmission (circuit breakers, transformers etc) is much lower than the equivalent DC transmission
c.AC produce magnetic flux,but d.c is not produce flux.
4)How can you relate power engineering with electrical engineering?
Power engineering is a sub division of electrical engineering. It deals with generation, transmission and distribution of energy in electrical form. Design of all power equipments also comes under power engineering.
5)What are the various kind of cables?
Cables, which are used for transmitting power, can be categorized in three forms:
• Low-tension cables, which can transmit voltage upto 1000 volts.
• High-tension cables can transmit voltage upto 23000 volts.
• Super tension cables can transmit voltage 66 kV to 132 kV.
6)Why back emf used for a dc motor?
According to faraday law,when current carrying conductor put in magnetig field then E.M.F will be induced in conductor is called back emf. Its value depends upon the speed of rotation of the armature conductors. In starting, the value of back emf is zero.
7)What is slip in an induction motor?
Diffrent between synchronous speed to rotor speed is called slip in an induction motor.itrepresented by the symbol ‘S’.
8)What is diffrent between ac and dc.
in Ac flow of current either positive to negative or negative to positive but have only phase.
Ac produce flux but dc not produce flux.
9. What is diffrent between 3-phase and 1-phase.
3-phase produce rotating torque but 1-phase not produce rotating torque.
10. What are the different methods for the starting of a synchronous motor.
Starting methods: Synchronous motor can be started by the following two methods:
• BY prime mover: The rotor of a synchronous motor is rotated by auxiliary motor. Then rotor poles are excited due to which the rotor field is locked with the stator-revolving field and continuous rotation is obtained.
• By damper winding: Here, bar conductors are embedded in the outer periphery of the rotor poles and are short-circuited with the short-circuiting rings at both sides. The machine is started as a squirrel cage induction motor first. When it picks up speed, excitation is given to the rotor and the rotor starts rotating continuously as the rotor field is locked with stator revolving field.
11. Name the types of motors used in vacuum cleaners?
Universal motor are used in vacuum cleaner.in univalsal motor dc motor work on ac power.
12. State Thevenin’s Theorem:
According to thevenin’s theorem, When two circuit are replaced by an equivalent circuit,it consist of an voltage source and series resister.
13. State Norton’s Theorem.
According to thevenin’s theorem, When two circuit are replaced by an equivalent circuit,it consist of an voltage source and parallel resister.
14. State Maximum power transfer theorem.
The Maximum power transfer theorem explains about the load that a resistance will extract from the network. This includes the maximum power from the network and in this case the load resistance is being is equal to the resistance of the network and it also allows the resistance to be equal to the resistance of the network. This resistance can be viewed by the output terminals and the energy sources can be removed by leaving the internal resistance behind.
15. Explain different losses in a transformer.
There are three types of losses occurring in transformer:
Iron loss
cu loss
eddy current loss
16. Explain different types of D.C motors?
Give their applicationsDifferent type of DC motors and their applications are as follows:-
• Shunt motors:When field winding and armature current connected in parallel is called shunt motor such as pumps, blowers, fan, lathe machines, tools, belt or chain conveyor etc.
• Series motor: When field winding and armature current connected in series is called shunt motor. Therefore, motor is used in lifts, cranes, traction work, coal loader and coal cutter in coalmines etc.
• Compound motors: Having both series and shunt is called compound motor. This motor will therefore find its application in loads having high inertia load or requiring high intermittent torque such as elevators, conveyor, rolling mill, planes, presses, shears and punches, coal cutter and winding machines etc.
17. Explain the terms real power, apparent power and reactive power for ac circuits and also the units used.•
Real power: It is the product of voltage, current and power factor i.e. P = V I cos j
Apparent power:it is product of voltage and current i.e. P=V I.
Reactive power: It is the product of voltage, current and Sine angle i.e. P = V I Sin j
18. What is the working principle of operation of a single-phase transformer.
Working principle of operation of a single-phase transformer can be explained as
An AC supply passes through the primary winding, a current will start flowing in the primary winding. As a result, the flux is set. This flux is linked with primary and secondary windings. Hence, voltage is induced in both the windings. Now, when the load is connected to the secondary side, the current will start flowing in the load in the secondary winding, resulting in the flow of additional current in the secondary winding. Hence, according to Faraday’s laws of electromagnetic induction, emf will be induced in both the windings. The voltage induced in the primary winding is due to its self inductance and known as self induced emf and according to Lenze’s law it will oppose the cause i.e. supply voltage hence called as back emf. The voltage induced in secondary coil is known as mutually induced voltage. Hence, transformer works on the principle of electromagnetic induction.
19. Define the following terms:-•
. Reliability,
• Maximum demand,
Reliability: It is the capacity of the power system to serve all power demands without failure over long periods.
Maximum Demand: It is maximum load demand required in a power station during a given period.
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INTERVIEW QUESTION
1)Why star delta starter is used to start induction motor?
Star delta starter is preferred with induction motor due to following reasons:
• It reduce 3-4 time starting voltage,starting current and also torque.
2)State the difference between generator and alternator?
Generator and alternator are two devices, which converts mechanical energy into electrical energy. Both have the same principle of electromagnetic induction, the only difference is that their construction.
Alternator:ac to ac conversion.
Generator:dc to ac conversion
3)Why AC systems is better DC systems?
Due to following reasons, AC systems are preferred over DC systems:
a. It is easy to maintain and change the voltage of AC electricity for transmission and distribution.
b. Plant cost for AC transmission (circuit breakers, transformers etc) is much lower than the equivalent DC transmission
c.AC produce magnetic flux,but d.c is not produce flux.
4)How can you relate power engineering with electrical engineering?
Power engineering is a sub division of electrical engineering. It deals with generation, transmission and distribution of energy in electrical form. Design of all power equipments also comes under power engineering.
5)What are the various kind of cables?
Cables, which are used for transmitting power, can be categorized in three forms:
• Low-tension cables, which can transmit voltage upto 1000 volts.
• High-tension cables can transmit voltage upto 23000 volts.
• Super tension cables can transmit voltage 66 kV to 132 kV.
6)Why back emf used for a dc motor?
According to faraday law,when current carrying conductor put in magnetig field then E.M.F will be induced in conductor is called back emf. Its value depends upon the speed of rotation of the armature conductors. In starting, the value of back emf is zero.
7)What is slip in an induction motor?
Diffrent between synchronous speed to rotor speed is called slip in an induction motor.itrepresented by the symbol ‘S’.
8)What is diffrent between ac and dc.
in Ac flow of current either positive to negative or negative to positive but have only phase.
Ac produce flux but dc not produce flux.
9. What is diffrent between 3-phase and 1-phase.
3-phase produce rotating torque but 1-phase not produce rotating torque.
10. What are the different methods for the starting of a synchronous motor.
Starting methods: Synchronous motor can be started by the following two methods:
• BY prime mover: The rotor of a synchronous motor is rotated by auxiliary motor. Then rotor poles are excited due to which the rotor field is locked with the stator-revolving field and continuous rotation is obtained.
• By damper winding: Here, bar conductors are embedded in the outer periphery of the rotor poles and are short-circuited with the short-circuiting rings at both sides. The machine is started as a squirrel cage induction motor first. When it picks up speed, excitation is given to the rotor and the rotor starts rotating continuously as the rotor field is locked with stator revolving field.
11. Name the types of motors used in vacuum cleaners?
Universal motor are used in vacuum cleaner.in univalsal motor dc motor work on ac power.
12. State Thevenin’s Theorem:
According to thevenin’s theorem, When two circuit are replaced by an equivalent circuit,it consist of an voltage source and series resister.
13. State Norton’s Theorem.
According to thevenin’s theorem, When two circuit are replaced by an equivalent circuit,it consist of an voltage source and parallel resister.
14. State Maximum power transfer theorem.
The Maximum power transfer theorem explains about the load that a resistance will extract from the network. This includes the maximum power from the network and in this case the load resistance is being is equal to the resistance of the network and it also allows the resistance to be equal to the resistance of the network. This resistance can be viewed by the output terminals and the energy sources can be removed by leaving the internal resistance behind.
15. Explain different losses in a transformer.
There are three types of losses occurring in transformer:
Iron loss
cu loss
eddy current loss
16. Explain different types of D.C motors?
Give their applicationsDifferent type of DC motors and their applications are as follows:-
• Shunt motors:When field winding and armature current connected in parallel is called shunt motor such as pumps, blowers, fan, lathe machines, tools, belt or chain conveyor etc.
• Series motor: When field winding and armature current connected in series is called shunt motor. Therefore, motor is used in lifts, cranes, traction work, coal loader and coal cutter in coalmines etc.
• Compound motors: Having both series and shunt is called compound motor. This motor will therefore find its application in loads having high inertia load or requiring high intermittent torque such as elevators, conveyor, rolling mill, planes, presses, shears and punches, coal cutter and winding machines etc.
17. Explain the terms real power, apparent power and reactive power for ac circuits and also the units used.•
Real power: It is the product of voltage, current and power factor i.e. P = V I cos j
Apparent power:it is product of voltage and current i.e. P=V I.
Reactive power: It is the product of voltage, current and Sine angle i.e. P = V I Sin j
18. What is the working principle of operation of a single-phase transformer.
Working principle of operation of a single-phase transformer can be explained as
An AC supply passes through the primary winding, a current will start flowing in the primary winding. As a result, the flux is set. This flux is linked with primary and secondary windings. Hence, voltage is induced in both the windings. Now, when the load is connected to the secondary side, the current will start flowing in the load in the secondary winding, resulting in the flow of additional current in the secondary winding. Hence, according to Faraday’s laws of electromagnetic induction, emf will be induced in both the windings. The voltage induced in the primary winding is due to its self inductance and known as self induced emf and according to Lenze’s law it will oppose the cause i.e. supply voltage hence called as back emf. The voltage induced in secondary coil is known as mutually induced voltage. Hence, transformer works on the principle of electromagnetic induction.
19. Define the following terms:-•
. Reliability,
• Maximum demand,
Reliability: It is the capacity of the power system to serve all power demands without failure over long periods.
Maximum Demand: It is maximum load demand required in a power station during a given period.
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