Synchronous Motor MCQ

106. Which motor is generally used in rolling mills, paper and cement industries?

1. D.C. shunt motor
2. Double squirrel cage motor
3. Slip-ring induction motor
4. Three-phase synchronous motor

107. A synchronous motor may fail to pull into synchronism owing to

1. Excessive load
2. Low excitation
3. High friction
4. Any of the options

108. The slip rings employed in a 3-phase synchron0us machine are insulated for

1. Output rated voltage
2. Low voltage
3. Very low voltage
4. Very high voltage

109. The stator core of a synchronous machine is built up of _______ laminations.

1. Stainless steel
2. Silicon steel
3. Cast iron
4. Cast steel

110. In case one phase of a 3-phase synchronous motor is short-circuited the motor will

1. Not Start
2. Run at two-third of synchronous speed
3. Run with excessive vibrations
4. Take less than the rated load

111. The open slots are more commonly used in the stator of a synchronous machine because

1. The inductance of the winding is less
2. They facilitate the insertion of form-wound and insulated coils.

1. Only i
2. Only ii
3. Both i and ii
4. None of these

112. In a synchronous motor, the stator frame is made of

1. Stainless steel
2. CRGOS
3. Cast iron or welded steel plates
4. Laminated silicon steel

113. The construction of synchronous motor is similar to

1. d.c. compound motor
2. slip-ring induction motor
3. d.c. shunt generator
4. alternator

114. The synchronous motor runs on

1. 3-phase a.c. supply
2. 3-phase a.c. and d.c. supply
3. d.c. supply only
4. 3-phase a.c. and single-phase a.c.

115. The power output of a synchronous motor is

1. directly proportional to synchronous reactance
2. inversely proportional to synchronous reactance
3. independent of synchronous reactance
4. None of these

116. Synchronous motors generally have

1. cylindrical rotor
2. salient pole rotor
3. Both cylindrical and salient pole rotor
4. None of these

117. Under full load running condition, the slip of a synchronous motor is

1. zero
2. about 0.2
3. about 0.01
4. None of these

118. If the excitation and terminal voltage of synchronous motor are kept constant and the load is increased then

1. armature current decreases and power factor becomes power leading
2. armature current increases and power factor becomes more leading
3. armature current increases and power factor becomes more lagging
4. None of these

119. When a synchronous motor is started, the field winding is initially

1. short-circuited
2. open-circuited
3. excited by a d.c. source
4. None of these

120. The amortisseur winding in a synchronous motor

1. provides starting torque only
2. provides starting torque and eliminates hunting
3. improves the power factor of the machine
4. None of these