Electrical Machine MCQ #18

1) In synchronous generator, to reduce hysteresis loss the stator core is assembled with

      (a) low grade silicon steel

      (b) high grade silicon steel

      (c) laminated core

      (d) cast iron

2) In case of 4-pole machine, how many cycles of emf is generated in one complete revolution of rotation?

      (a) one cycle

      (b) two cycles

      (c) three cycles

      (d) four cycles

3) Which equation gives the relation between electrical degree and mechanical degree?

      (a) Electrical degree = P/6 x mechanical degree

      (b) Electrical degree = P/4 x mechanical degree

      (c) Electrical degree = P/2 x mechanical degree

      (d) Electrical degree = P x mechanical degree

4) For a 2-pole machine, 360° of electrical cycle is equal _______ of mechanical rotation?

      (a) 90°

      (b) 180°

      (c) 270°

      (d) 360°

ANSWER: | 1-b | 2-b | 3-c | 4-d |

5) The pole pitch is defined as _____.

      (a) It is the peripheral distance between the two adjacent poles

      (b) The periphery of the armature divided by the number of poles

      (c) Both A and B

      (d) It is the distance between the two coil sides

6) Why the starters are used in the induction motor?

      (a) to provide under voltage protection

      (b) to reduce the heavy starting current

      (c) to provide over load protection

      (d) all of the above

7) Which starters commonly used for the cage type induction motors?

      (a) Autotransformer

      (b) star-delta starter

      (c) direct online starter

      (d) all of the above

8) A star-delta starter is used for _____, designed to run normally on _____ winding.

      (a) cage rotor motor; delta connected rotor

      (b) wound rotor motor; delta connected stator

      (c) cage rotor motor; delta connected stator

      (d) wound rotor motor; delta connected rotor

ANSWER: | 5-c | 6-d | 7-d | 8-c |

9) In autotransformer starter the starting current is limited to reduced

      (a) the initial stator currents

      (b) the field current

      (c) the initial load currents

      (d) the initial stator voltage applied

10) A star delta starter is

      (a) commonly used for small and medium size motors

      (b) cheaper than auto transformer

      (c) Both A and B

      (d) costly than autotransformer

11) Which test is performed to calculate the efficiency of the motors?

      (a) no-load test

      (b) blocked rotor test

      (c) regenerative test

      (d) Both A and B

12) which test is performed to calculate friction and windage loss?

      (a) blocked rotor test

      (b) open circuit test

      (c) regenerative test

      (d) any of the above

ANSWER: | 9-d | 10-c | 11-d | 12-b |