McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Electrical Engineering .
| 101. |
If the field of a synchronous motor is underexcited, the power factor will be |
| A. | zero |
| B. | unity |
| C. | lagging |
| D. | leading |
| Answer» C. lagging | |
| 102. |
The back e.m.f. in the stator of a synchronous motor depends on |
| A. | number of poles |
| B. | flux density |
| C. | rotor speed |
| D. | rotor excitation |
| Answer» D. rotor excitation | |
| 103. |
The maximum value of torque that a synchronous motor can develop without losing its synchronism, is known as |
| A. | slip torque |
| B. | pull-out torque |
| C. | breaking torque |
| D. | synchronising torque |
| Answer» D. synchronising torque | |
| 104. |
In a synchronous motor, the armature current has large values for |
| A. | high excitation only |
| B. | low excitation only |
| C. | both high and low excitation |
| D. | none of the above |
| Answer» C. both high and low excitation | |
| 105. |
Which of the following losses, in a synchronous motor, does not vary with load? |
| A. | Windage loss |
| B. | Copper losses |
| C. | Any of the above |
| D. | None of the above |
| Answer» A. Windage loss | |
| 106. |
The size of a synchronous motor decreases with the increase in |
| A. | flux density |
| B. | horse power rating |
| C. | speed |
| D. | all of the above |
| Answer» A. flux density | |
| 107. |
Which of the following losses is not dissipated by the stator core surface in a synchronous motor ? |
| A. | Eddy current losses in the conductors |
| B. | Iron losses in the stator |
| C. | Copper losses in the slot portion of the conductors |
| D. | Windage losses |
| Answer» D. Windage losses | |
| 108. |
The duration of sudden snort-circuit test on a synchronous motor is usually about |
| A. | one hour |
| B. | one minute |
| C. | one second |
| D. | none of the above |
| Answer» C. one second | |
| 109. |
A synchronous machine with low value of short-circuit ratio has |
| A. | lower stability limit |
| B. | high stability limit |
| C. | good speed regulation |
| D. | good voltage regulation |
| Answer» A. lower stability limit | |
| 110. |
The construction of a synchronous motor resembles |
| A. | a series motor |
| B. | an induction motor |
| C. | an alternator |
| D. | a rotary converter |
| Answer» C. an alternator | |
| 111. |
If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will |
| A. | stop |
| B. | run as induction motor |
| C. | function as static condenser |
| D. | burn with dense smoke |
| Answer» A. stop | |
| 112. |
For power factor correction, synchronous motors operate at |
| A. | no-load and greatly over-excited fields |
| B. | no-load and under-excited fields |
| C. | normal load with minimum excitation |
| D. | normal load with zero excitation |
| Answer» A. no-load and greatly over-excited fields | |
| 113. |
The maximum torque which a synchronous motor will develop at rest for any angular position of the rotor, at rated stator supply voltage and frequency, is known as |
| A. | locked-rotor torque |
| B. | synchronous torque |
| C. | pull up torque |
| D. | reluctance torque |
| Answer» A. locked-rotor torque | |
| 114. |
Exciters of synchronous machines are |
| A. | d.c. shunt machines |
| B. | d.c. series machines |
| C. | d.c. compound machines |
| D. | any of the above |
| Answer» A. d.c. shunt machines | |
| 115. |
The coupling angle or load angle of synchronous motor is defined as the angle between the |
| A. | rotor and stator teeth |
| B. | rotor and the stator poles of opposite polarity |
| C. | rotor and the stator poles of the same polarity |
| D. | none of the above |
| Answer» B. rotor and the stator poles of opposite polarity | |
| 116. |
If the synchronous motor, properly synchronised to the supply is running on no load and is having negligible loss then |
| A. | the stator current will be zero |
| B. | the stator current will be very small |
| C. | the stator current will be very high |
| D. | the back e.m.f. will be more than the supply voltage |
| Answer» A. the stator current will be zero | |
| 117. |
The armature current of the synchronous motor |
| A. | has large values for low excitation i niy |
| B. | has large values for high excitation only |
| C. | has large values for low and high excitation |
| D. | any of the above |
| Answer» C. has large values for low and high excitation | |
| 118. |
The maximum power developed in a synchronous motor will depend on |
| A. | the rotor excitation only |
| B. | the supply voltage only |
| C. | the rotor excitation and supply volt-age both |
| D. | the rotor excitation, supply voltage and maximum value of coupling angle (90°) |
| Answer» D. the rotor excitation, supply voltage and maximum value of coupling angle (90°) | |
| 119. |
A synchronous motor which works on a leading power factor and does not drive a mechanical load is called as |
| A. | static condenser |
| B. | condenser |
| C. | synchronous condenser |
| D. | none of the above |
| Answer» C. synchronous condenser | |
| 120. |
A synchronous motor develops maximum power when load angle is |
| A. | 45° |
| B. | 60° |
| C. | 90° |
| D. | 120° |
| Answer» C. 90° | |
| 121. |
In a synchronous motor, the breakdown torque is |
| A. | directly proportional to applied voltage |
| B. | directly proportional to the square of the applied voltage |
| C. | inversely proportional to applied voltage |
| D. | none of the above |
| Answer» A. directly proportional to applied voltage | |
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