The main cause of hunting in synchronous motor is

 

101. The most suitable method for starting large synchronous motors is
     A) Using pony motor
     B) Direct-on-line starting
     C) Resistance starting
     D) Autotransformer starting

A

102. The damper winding acts as
     A) Secondary of induction motor
     B) Field winding
     C) Armature winding
     D) None

A

103. The stator winding of a synchronous motor is
     A) Star connected
     B) Delta connected
     C) Either star or delta
     D) Open delta

C

104. The field poles of a cylindrical rotor are
     A) Uniform air gap type
     B) Non-uniform air gap type
     C) Laminated type
     D) Permanent magnet type

A

105. The field poles of a salient pole rotor are
     A) Uniform air gap
     B) Projected poles
     C) Smooth poles
     D) Cylindrical

B

106. In synchronous motor, increasing excitation causes
     A) Leading power factor
     B) Lagging power factor
     C) More torque
     D) Less torque

A

107. The magnetic locking in a synchronous motor fails if
     A) Load torque > pull-out torque
     B) Field excitation too high
     C) Supply frequency low
     D) Both A and C

D

108. The rotor of a synchronous motor is made to rotate initially by
     A) DC excitation
     B) AC excitation
     C) Damper winding
     D) Slip rings

C

109. When a synchronous motor loses synchronism, it acts as
     A) Induction motor
     B) Induction generator
     C) Transformer
     D) DC generator

A

110. The main cause of hunting in synchronous motor is
     A) Sudden load changes
     B) Low excitation
     C) High frequency
     D) Low voltage

A

111. The synchronizing torque in a synchronous motor is proportional to
     A) Cos δ
     B) Sin δ
     C) δ
     D) tan δ

A

112. The operation of a synchronous motor can be compared to
     A) DC series motor
     B) DC shunt motor
     C) Induction motor
     D) Transformer on short circuit

D

113. The speed regulation of a synchronous motor is
     A) Good
     B) Poor
     C) Zero
     D) Variable

C

114. The torque angle δ increases when
     A) Load increases
     B) Excitation increases
     C) Speed increases
     D) Supply voltage increases

A

115. The value of pull-out torque depends on
     A) Excitation
     B) Supply voltage
     C) Synchronous reactance
     D) All of the above

D

116. The relation between electrical and mechanical degrees is
     A) Electrical = (P/2) × mechanical
     B) Mechanical = (P/2) × electrical
     C) Electrical = mechanical
     D) None

A

117. The primary cause of vibration in synchronous motors is
     A) Hunting
     B) Poor lubrication
     C) Misalignment
     D) Stator slots

A

118. The excitation voltage is directly proportional to
     A) Field current
     B) Speed
     C) Supply voltage
     D) Torque

A

119. The maximum power developed in synchronous motor is
     A) EV/Xs
     B) (EV/Xs) sin δ
     C) (EV/Xs) cos δ
     D) E²/Xs

A

120. The excitation emf (E) of a synchronous motor is given by
     A) √(V² + (IaRa)² + (IaXs)²)
     B) V – Ia(Ra + jXs)
     C) √(V² – 2VIacosφ + (IaXs)²)
     D) None

B

121. The torque developed per phase is
     A) (EV/Xs) sin δ
     B) (3EV/Xs) sin δ
     C) (E/Xs) cos δ
     D) (EV/Ra) sin δ

A

122. When a synchronous motor is over-excited, it draws
     A) Lagging current
     B) Leading current
     C) Unity current
     D) Zero current

B

123. The active power drawn by a synchronous motor depends on
     A) Load angle δ
     B) Excitation
     C) Supply voltage
     D) All

A

124. The reactive power drawn by a synchronous motor depends on
     A) Excitation
     B) Load torque
     C) Frequency
     D) Armature resistance

A

125. The power factor of a synchronous motor is controlled by
     A) Field current
     B) Armature current
     C) Load
     D) Supply frequency

A

126. The line current of a synchronous motor is minimum when
     A) Operating at unity power factor
     B) Operating at lagging power factor
     C) Operating at leading power factor
     D) None

A

127. Synchronous motor operates at
     A) Constant speed below synchronous
     B) Constant synchronous speed
     C) Variable speed
     D) Slightly above synchronous speed

B

128. The effect of armature reaction in a synchronous motor is
     A) Demagnetizing or magnetizing
     B) Cross-magnetizing
     C) Lagging only
     D) Leading only

A

129. Synchronous motor consumes lagging VARs when
     A) Over-excited
     B) Under-excited
     C) Normal excitation
     D) None

B

130. Synchronous motor supplies leading VARs when
     A) Over-excited
     B) Under-excited
     C) Normally excited
     D) None

A

131. The field excitation is adjusted so that
     A) Motor runs at unity power factor
     B) Motor runs at constant torque
     C) Motor speed increases
     D) Motor runs at zero load

A

132. For power factor correction, synchronous motor is operated as
     A) Synchronous condenser
     B) DC motor
     C) Induction generator
     D) Stepper motor

A

133. The torque in a synchronous motor is proportional to
     A) sin δ
     B) cos δ
     C) tan δ
     D) δ

A

134. The electrical angle corresponding to one mechanical revolution of a 6-pole machine is
     A) 180°
     B) 360°
     C) 1080°
     D) 720°

C

135. In case of leading power factor, armature current leads
     A) Supply voltage
     B) Field current
     C) Back emf
     D) None

A

136. The magnetic coupling between stator and rotor fields is known as
     A) Magnetic locking
     B) Electric locking
     C) Inductive coupling
     D) Synchronism

A

137. Synchronous motor is preferred where
     A) Constant speed is required
     B) Speed control is required
     C) Variable torque required
     D) High starting torque required

A

138. When synchronous motor is running, speed changes if
     A) Frequency changes
     B) Excitation changes
     C) Voltage changes
     D) Load changes

A

139. The field current required for lagging power factor operation is
     A) Less than unity excitation
     B) More than unity excitation
     C) Equal to unity excitation
     D) Zero

A

140. For a given torque, the load angle δ is
     A) Inversely proportional to excitation
     B) Directly proportional to excitation
     C) Inversely proportional to voltage
     D) Independent of excitation

A

141. The pull-out torque is directly proportional to
     A) Supply voltage²
     B) Supply frequency
     C) Field resistance
     D) Armature resistance

A

142. The damper winding reduces
     A) Hunting
     B) Torque
     C) Speed
     D) Load

A

143. The induced emf in a synchronous motor is proportional to
     A) Field current
     B) Load
     C) Frequency
     D) Torque

A

144. If the direction of rotation of a synchronous motor is to be reversed,
     A) Reverse any two stator leads
     B) Reverse field polarity
     C) Both A and B
     D) None

C

145. When load on synchronous motor increases, the armature current
     A) Increases
     B) Decreases
     C) Remains constant
     D) Becomes zero

A

146. The current drawn by the synchronous motor at no-load is mainly
     A) Magnetizing current
     B) Active current
     C) Power current
     D) Reactive current

A

147. When load is suddenly removed, the synchronous motor may
     A) Overspeed
     B) Hunt
     C) Reverse
     D) Stop

B

148. The voltage across field winding is generally
     A) 220 V DC
     B) 110 V DC
     C) 440 V DC
     D) 600 V DC

A

149. The main disadvantage of salient pole rotor is
     A) Non-uniform air gap
     B) High losses
     C) Poor cooling
     D) High cost

A

150. The cylindrical rotor is preferred for
     A) High-speed machines
     B) Low-speed machines
     C) Medium-speed machines
     D) Variable speed machines

A