Electrical Machines Questions and Answers – Induction Generator

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This set of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on “Induction Generator”.

1. A 3-phase induction motor can also be run as ______________
a) synchronous generator
b) induction generator
c) dc shunt motor
d) any of the mentioned
View Answer

Answer: b
Explanation: For the same machine if the slip is made negative by raising the speed above synchronous speed.
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2. Induction generator ____________
a) can not work in isolation
b) can work in isolation
c) should work in parallel with synchronous generators
d) any of the mentioned
View Answer

Answer: c
Explanation: Induction generator needs the continuous flux and it can be either provided by the bus or the synchronous generator.

3. A self excited induction generator ____________
a) must have static capacitor bank
b) can have static capacitor bank
c) should have static capacitor bank
d) any of the mentioned
View Answer

Answer: a
Explanation: To provide the lagging reactive power, it is must that it should be have a source of lagging reactive power.
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4. For an induction motor to work in isolation, it should have ____________
a) lagging reactive power source
b) leading reactive power source
c) leading reactive power sink
d) any of the mentioned
View Answer

Answer: a
Explanation: It must be connected to capacitors which can be the source for lagging reactive power.

5. The magnetization curve in the induction generator working in isolation has similar characteristic as ____________
a) dc shunt generator
b) dc cumulative field generator
c) synchronous generator
d) all of the mentioned
View Answer

Answer: a
Explanation: The voltage build up process of the induction generator is similar to that of the dc shunt generator.
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6. If the residual flux is absent in the rotor iron of the isolated induction generator ____________
a) it will not run
b) it will run as induction motor
c) it will burn the winding
d) it will not affect the characteristic of the generator
View Answer

Answer: a
Explanation: If the residual flux of the isolated induction generator is not present, then voltage build up will not take place.

7. Voltage build up in an isolated induction generator depends on ____________

A. Capacitor bank value
B. Residual magnetism of the rotor iron
C. Residual magnetism of the stator iron
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a) A, B
b) A, B, C
c) B
d) A, C
View Answer

Answer: a
Explanation: Voltage build up will depend on capacitance and the residual magnetism of the rotor iron.

8. I. Voltage of an externally excited induction generator can not be controlled.
II. Frequency of an externally excited induction generator can be controlled.
a) I is true, II is false
b) I is true, II is true
c) I is false, II is false
d) I is false, II is true
View Answer

Answer: a
Explanation: Voltage and frequency of the externally excited induction generator can not be controlled, because they run in parallel with the existing 3-phase systems.
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9. What is/are the shortcomings of an induction generator in real time system?
a) It needs considerable amount of reactive power
b) Efficiency is poor
c) It can work at leading power factor only
d) All of the mentioned
View Answer

Answer: d
Explanation: All are the disadvantages of an induction generator.

10. Induction generator is self excited machine.
a) True
b) False
View Answer

Answer: b
Explanation: No, induction machine is first run as motor and then as generator. So it needs the current to set up the flux continuously.

11. Induction generator can only work at leading reactive power.
a) True
b) False
View Answer

Answer: a
Explanation: Because it can not supply any lagging power factor.

12. Choose the correct match for the corresponding characteristics of a 3-phase induction motor.
The corresponding characteristics of a 3-phase induction motor is A-II, B-III & C-I

   x-axis                         y-axis                  
 A.  stator current            power output            (P) Curve I
 B.  torque                    slip                    (Q) Curve II
 C.  speed                     power output            (R) Curve III

a) A-II, B-III, C-I
b) A-III, B-II, C-I
c) A-III, B-I, C-II
d) A-I, B-II, C-III
View Answer

Answer: a
Explanation: Speed will remain constant for a fair amount of operating range. Torque will be linear in small slip regions.

13. Which is the most acceptable application field where an induction generator can be used?
a) wind power system
b) steam power system
c) hydro power system
d) nuclear power station
View Answer

Answer: a
Explanation: Induction generator is widely acceptable in low speed and low power operation like wind power systems.

14. A 3-phase induction motor has full load efficiency of 0.7 and a maximum efficiency of 0.85. It is operated at a slip of 0.6 by reduced voltage method. The efficiency of the motor at this operating point is?
a) less than 0.35
b) greater than 0.35
c) in the range of 0.8 to 0.2
d) none of the mentioned
View Answer

Answer: a
Explanation: For the slip more than 40%, the efficiency reduces more than 50% for an induction motor.

15. Two three phase squirrel-cage induction generator are identical in all respects except the fact that the slot depths in machine B is more than that of A. Machine B as compared to machine A, will have _________
a) less pull out torque but better power factor
b) more pull out torque but poor power factor
c) less pull out torque and poor power factor
d) more pull out torque and better power factor
View Answer

Answer: a
Explanation: As the slot depth in machine B is more than that of A, B will have higher reactance as the leakage flux will be lesser.

Sanfoundry Global Education & Learning Series – Electrical Machines.

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