# MCQs on Electrical Machines 4

1. Which speed control method preferred for constant torque drive?

Under construction.

2. A differentially compounded motor under high overload condition will behave like a / an

Under construction.

3. If an ac servomotor has one of its winding excited by AC, then voltage measured at the other winding with rotor running will be

Under construction.

4. An inverted V curve of synchronous motor shows variation of

Under construction.

5. A small air gap in poly phase induction motor helps to

Under construction.

6. While operating on variable frequency supplies, the AC motor requires variable voltage in order to?

Under construction.

7. Which of the following motors are suitable for computer printer drive ?

Under construction.

8. The direction of rotation of a dc motor can be determined by

Under construction.

9. A thermal protection switch is used to provide protection against

Under construction.

10. A 500 V, 55 kVA single phase alternator has an effective resistance of 0.5 ohm. An excitation current of 10 A produces 200 A armature current on short circuit and an emf of 450 V on per circuit. The synchronous reactance will be

Under construction.

11. Methods of synchronizing of alternator

Under construction.

12. What is the utilization factor of a power station which supplies the following loads?
Load A motor load of 200 KW between 10 am to 7 pm.
Load B lighting load of 100 KW between 7 pm to 11 pm.
Load C pumping load of 110 KW between 3 pm to 10 pm.

Under construction.

13. What are the starters used for starting of cage motors?

Under construction.

14. Piezoelectric effect is carried out in

Under construction.

15. The direction of rotation of a 3 - Φ induction motor is clockwise when it is supplied with 3 phase sinusoidal voltage having phase sequence A - B - C . For counterclockwise rotation of motor, the phase sequence of the supply should be ?

To reverse direction of rotation phase sequence of the supply has to be reversed.

16. The synchronous speed for the seventh space harmonic mmf wave of 8 pole, 50 Hz induction machine will be

Synchronous speed Ns = 120f / P = 120 × 50 / 8 = 750 rpm. Mmf wave contains space harmonics e.g. fifth and seventh harmonics which corresponds to pole five and seven times that of the fundamental. So seventh harmonic pole rotate forward at speed Ns / 7 = 750 / 7 = 107.14 rpm.

17. In a single phase induction motor driving a fan load, the reason for having a high resistance rotor is to achieve

Higher the torque resistance, more is the total torque developed which results in quick acceleration.

18. Asynchronous generator is feeding a zero power factor (lagging) load at rated current. The armature reaction is

Under construction.

19. A 4 point starter is used to start and control the speed of a

Under construction.