MOTORS AND GENERATORS

1)            

DC motor

Comstruction - Synchronous motor

Induction Motor

        1. Centrifugal switch is absent in which of the single phase induction motor?

1.    Shaded pole motor.

2.    PSC (permanent split capacitor) motor.

3.    Split phase motor.

4.    None of the above.

2)             A motor armature conductor of length 0.5 m is exposed to a flux density of 4 Wb / m². Calculate the force experienced by the conductor, when the armature current is 5 Amp?

1) 15 N.

2) 20 N.

3)  Can’t be determined.

4)  None of these.

3) In case of induction motors the ratio of length to pole pitch for minimum cost, is taken as

1.    1.0.

2.    1.5 to 2.

3.    2 to 3.

4.    3 to 5.

4)          The use of double squirrel cage winding on the rotor provides

1.  low noise.

2.  reduced starting torque.

3.  a large starting torque.

4.  higher efficiency.

5)          Which of the following machine is invariably provided with forced ventilation?

1.  Fractional horse power slow speed motor.

2.  Fractional horse power high speed motor.

3.  Hermetically sealed motor of refrigerator.

4.  50 MW generator in a power plant.

6)             In induction motors, there is large decrease in maximum power factor when the dispersion coefficient is ________________.

1.  decreased.

2.  increased.

3.  remains same.

4.  kept constant to certain value.

7)             In induction motor when the length of the air gap is increased, the magnetizing current of the motor increases while the short circuit current __________________.

1.  increased.

2.  decreased.

3.  kept constant to certain value.

4.  remains unchanged.

8)             In electrical machines the material preferred for pole shoes of electromagnets is

1.  copper.

2.  aluminium.

3.  pure iron.

4.  lead.

9)             Which of the following gives materials in order of decreasing values of permeability?

1.  Permalloy, nickel, air, water.

2.  Cobalt, nickel, aluminium, iron.

3.  Pure iron, silicon iron, aluminium, bismuth.

4.  Silver, copper, aluminium, iron.

10) Hunting phenomenon is observed in which motor?

1.  Synchronous motor.

2.  DC motor.

3.  Induction motor.

4.  Both A and C.

11. Reluctance and hysteresis motors are the types of which electrical motor?

1.  1 - Φ synchronous motor.

2.  3 - Φ induction motor.

3.  Stepper motor.

4.  DC motor.

12. In most condition which frame of motor will be preferred?

1.  Open type.

2.  Totally enclosed fan cooled.

3.  Drip proof.

4.  Splash proof.

13. The wattage rating of a ceiling fan motor will be

1.  200 - 250 W.

2.  250 - 500 W.

3.  50 - 150 W.

4.  10 - 20 W.

14. A load of 900 lbs is to be raised with a lift car weighting 855 lbs at a speed of 110 feet per minute, the over balance being 40 % and percentage efficiency 45 %. Find the horse power of the motor without counterweight

1.  10 HP.

2.  13 HP.

3.  14 HP.

4.  15 HP.

15. Magnetic circuit with cross sectional area of 20 cm² is to be operated at 50 Hz from 120 V_rms supply. The number of turns required to active a peak magnetic flux density of 1.8 T in the core flux is

1.  150.

2.  160.

3.  170.

4.  180.

16. Mechanical energy is supplied to DC generator at the rate of 4200 J / s. The generator delivers 32.2 Amp at 120 V. What is the percentage efficiency of the generator?

1.  92 %.

2.  95 %.

3.  96 %.

4.  98 %.

17. If a shunt generator delivers 100 A at 200 V, and the resistances of the shunt field and armature are 100 ohms and 0.01 ohms respectively, the generator emf will be

1.  201.02 V.

2.  205 V.

3.  210 V.

4.  212 V.

18. We can apply source transformation to voltage source when a resistance is connected to it in

1.  series.

2.  parallel.

3.  any one of the connection.

4.  no resistance is connected.

19. Universal motor have which of the following application?

1.  Domestic pump.

2.  Food mixer.

3.  Traction.

4.  Lift.

20. A 3 stack stepper motor has 12 teeth on stator as well as on rotor. Determine the step size when each stack excited?

1.  10°.

2.  24°.

3.  30°.

4.  45°.

 ANSWERS

1.2              2.4           3.2           4.3           5.3           6.2

7.4              8.3           9.1           10.1         11.1         12.2

13.3            14.1         15.1         16.1         17.1         18.1

19.2            20.1