Electrical Machines Mock Test 8

10%

Question 1 of 10

1. The 3-phase induction motor operates at lagging power factor due to ________

I. Leading magnetizing current necessary to produce the working flux.
II. Voltage drops in the leakage impedance.
III. Lagging magnetizing current which lags by 90° to the voltage

II, III

I, II

I, II, III

Question 1 of 10

Question 2 of 10

2. A 10 kW, 400 V, 3-phase, 4-pole, 50 Hz induction motor develops the rated output at rated voltage with its slip rings shorted. The maximum torque equal to twice the full load torque occurs at the slip of 10% with zero external resistance in the rotor circuit. The slip at the full load torque will be?

3.7%

2.7%

10%

Question 2 of 10

Question 3 of 10

3. I. Maximum torque can be achieved by inserting an additional resistance at desired slip in the rotor.
II. Maximum torque can be altered by adding the external resistance in the rotor.

Only II is true

Both I and II are true

Only I is true

Neither I nor II is true

Question 3 of 10

Question 4 of 10

4. I. An induction can never operate at leading power factor.
II. Speed of the induction motor can be made more than synchronous speed and still it will work as motor.

I is true, II is false

I is true, II is true

I is false, II is true

I is false, II is also false

Question 4 of 10

Question 5 of 10

5. At which point shall the induction machine be operated to attain a stable operation?

The machine will not start

Both A as well as B

Question 5 of 10

Question 6 of 10

6. In the following circle diagram of the induction motor, QN is the ____________

rotor current referred to stator

stator current

stator current referred to rotor

no load input to rotor

Question 6 of 10

Question 7 of 10

7. A 3-phase induction machine is operating on 3-phase fixed frequency ac mains at a per unit slip of 1.5. Then machine is operating in generating mode.

False

True

Question 7 of 10

Question 8 of 10

8. If the no load test is conducted at its rated voltage but less than the rated frequency.

A. The wattmeter reading will be more than previous.
B. The power factor will also improve.

Both A as well as B are true

Only A is true

None of the mentioned

Only B is true

Question 8 of 10

Question 9 of 10

9. Induction motor can be fed from ___________

either rotor or stator

stator

neither stator nor rotor

rotor

Question 9 of 10

Question 10 of 10

10. A 3-phase induction motor is fed at the stator at a frequency f. If the rotor speed is Nr and synchronous speed is Ns, then the absolute speed of the resultant flux in space is?

(Ns-Nr) if the flux rotates in the same same direction as the rotor

(Ns+Nr) if the flux rotates in the same same direction as the rotor

Question 10 of 10