301 MCQ Questions on Synchronous Machine

101. What the damper bars develops, when the rotor speed, in a synchronous machine, becomes more than the synchronous speed during hunting? [UPPCL JE 2018]

(a) Inductor motor torque
(b) Induction generator torque
(c) D.C. motor torque
(d) Synchronous motor torque

102. A synchronous motor can operate at

(a) Lagging power factor only.
(b) Lagging, leading and unity power factors.
(c) Leading power factor only.
(d) None of these. [UPPCL JE – 2018]

103. According to Fleming’s right hand rule, what does the thumb indicate?

(a) Direction of the motion of the conductor relative to the magnetic field.
(b) Direction of the induced or generated current within the conductor.
(c) Direction of the magnetic field.
(d) None of these. [UPPCL JE – 2018]

104. The constant speed of a synchronous motor can be changed to new fixed value by which of the following methods? [UPPCL JE – 2018]

(a) By changing the applied voltage.
(b) By interchanging any two phases.
(c) By changing the supply frequency.
(d) All of these.

105. Which of the following generator is used in the thermal power plant? [UPPCL JE 2018]

(a) Turbo generator.
(b) Synchronous motor.
(c) Non-salient pole synchronous generator.
(d) Salient pole synchronous generator.

106. Calculate the frequency in Hz of a 10-pole AC generator which rotates at 1800 rpm. [UPPCL JE 2018]

(a) 120
(b) 100
(c) 150
 (d) 180

107. In a synchronous motor, the breakdown torque is

(a) Inversely proportional to the square of the applied voltage.
(b) Inversely proportional to applied voltage.
(c) Directly proportional to applied voltage.
(d) Directly proportional to the square of the applied voltage. [UPPCL JE – 2018]

108. If field current of a three phase alternator is reversed, what happens to its phase sequence? [UPPCL JE 2018]

(a) Remains same.
(b) Reverses.
(c) Two phases are exchanged.
(d) It becomes ac motor.

109. A 10 pole, 25 Hz alternator is directly coupled to and is driven by 60 Hz synchronous motor. Then the number of poles in a synchronous motor are

(a) 12 poles
(b) 48 poles
(c) 24 poles
(d) 6 poles

110. Which of the following phenomenon shows the regulation of an alternator? [UPPCL JE 2018]

(a) The increase in terminal voltage when load is thrown off.
(b) The variation of terminal voltage under the conditions of over and under excitation.
(c) Terminal voltage at zero power factor.
(d) The reduction in terminal voltage when alternator is on full load.

111. The synchronous motor has

(a) Constant speed
(b) Variable speed
(c) Constant poles
(d) Constant size

112. Which of the following motors one will choose to drive the rotary compressor?

(a) D.C. shunt motor
(b) D.C. series motor
(c) Universal motor
(d) Synchronous motor

113. Negative voltage regulation is indicative that the load is

(a) Capacitive only
(b) Inductive only
(c) Inductive or resistive
(d) None of the above

114. As load p.f. of an alternator becomes more leading, the value of generated voltage required to give rated terminal voltage

(a) Increases
(b) Remains unchanged
(c) Decreases
(d) Varies with rotor speed

115. Synchronous condenser means

(a) A synchronous motor with capacitor connected a cross stator terminals to improve PF.
(b) A synchronous motor operating at full load with leading PF.
(c) An over excited synchronous motor partially supplying mechanical load and also improving PF of the system to which it is connected.
(d) An over excited synchronous motor operating at no load with leading PF to improve the PF of the system.

116. In alternators during armature reaction the effect of armature flux on main flux with unity power factor is:

(a) Cross magnetizing.
(b) Wholly demagnetizing.
(c) Partially magnetizing.
(d) Wholly magnetizing. [Jharkhand JE 2017]

117. An integral number of slots per pole is often used in an alternator in order to

(a) Eliminate harmonics in the waveform.
(b) Provide insulation.
(c) Permit easy installation of stator coils.
(d) Provide easy removal in case of repair. [UPPCL JE – 2016]

118. Damper in a large generator is used to ……

(a) Increase stability.
(b) Reduce voltage fluctuation.
(c) Reduce frequency fluctuation
(d) All above. [Uttrakhand AE 2013]

119. Harmonics present in alternators affect

(a) Pitch factor.
(b) Chording factor.
(c) Neither Chording factor nor pitch factor.
(d) Chording factor and pitch factor. [UPRVUNL JE – 2016]

120. Synchronous generator can…….. reactive power. [UPRVUNL JE 2016]

(a) Neither generates nor absorbs.
(b) Absorb.
(c) Generate and absorb.
(d) Generate.

121. Select the correct choice of alternators for power generation using hydro and steam.

(a) Kaplan and Francis are both steam turbines.
(b) Kaplan and Francis are hydro turbines.
(c) Only Francis turbine is the hydro turbine.
(d) Kaplan for steam and Francis for hydro. [UPRVUNL JE 2016]

122. ……….. excitation will ……… the terminal voltage of the machine when connected ………..

(a) Variable – not change – to infinite bus.
(b) Fixed – change – independently.
(c) Variable – change – to Infinite bus.
(d) Variable – not change  – independently.

123. The pitch factor or chording factor of a short pitch winding in an alternator is defined as………..

(a) (Vector sum of induced emf per coil) × (Arithmetic sum of induced emf per coil)
(b) (Vector sum of induced emf per coil) / (Arithmetic sum of induced emf per coil)
(c) (Vector sum of induced emf per coil) + (Arithmetic sum of induced emf per coil)
(d) (Vector sum of induced emf per coil) – (Arithmetic sum of induced emf per coil) [UPRVUNL JE 2016]

124. An alternator has ………

(a) Rotating armature and stationary field .
(b) Stationary armature and stationary field.
(c) Rotating armature and rotating field.
(d) Stationary armature and rotating field. [UPRVUNL JE 2016]

125. To determine voltage regulation of an alternator the following experimental results are required:

(a) Short circuit characteristic and open circuit characteristic.
(b) Open circuit characteristic and armature impedance.
(c) Armature impedance.
(d) Short circuit characteristic and open circuit characteristic and Armature impedance. [UPRVUNL JE – 2016]

126. To reduce the peripheral speed of an alternator, diameter of the rotor is …………

(a) Increased.
(b) Decreased.
(c) Increased or decreased.
(d) Kept same. [UPPCL-JE 2016]

127. What is the frequency of voltage generated by an alternator having 6-poles and rotating at 900 rpm? [MPPKVVCL-2007]

(a) 50 rad/s
(b) 50 Hz
(c) 45 Hz
(d) 45 rad/s

128. The speed of two pole alternator at 60 Hz is ………

(a) 3600 rpm
(b) 750 rpm
(c) 300 rpm
(d) 1500 rpm [JUVNL-JE 2017]

129. The distribution or winding factor is defined in an alternator in terms of

(a) Power factor
(b) Electromotive force
(c) Power
(d) Current [JUVNL-JE 2017]

130. In case of leading load power factor, the terminal voltage of an alternator will

(a) Fall on removing the full load.
(b) Rise on removing the full load.
(c) Rise on adding the full load.
(d) Fall on adding the full load. [DMRC JE- 2017]

131. A magnetic flux on 300 m Wb in a coil of 100 turns is reverted in 0.2 seconds. The average emf induced is

(a) 600 V
(b) -300 V
(c) -600 V
(d) 300 V [DMRC JE- 2017]

132. Distributed winding and short chording employed in AC machines will result in………

(a) Reduction in both emf and harmonics emf.
(b) Reduction in emf and increase in harmonics emf.
(c) Increase in both emf and harmonics emf.
(d) Increase in emf and reduction in harmonics emf. [Coal India – 2017]

133. An alternator has a phase sequence of RYB for its phase voltages. In case the field current is reversed the phase sequence will become ……

(a) RBY
(b) RYB
(c) YRB
(d) None of the above [UJVNL-2016]

134. What is the pitch factor of a 4 pole alternator having 36 slots and a coil span of 1 to 8? [J&K JE 2016]

(a) 140°
 (b) 80°
(c) 20°
(d) 40°

135. A 3 Phase, 60 Hz generator connected in Y connection, generated a line to line voltage of 23900 V. Calculate the peak line voltage. [J&K JE – 2016]

(a) 13800 V
(b) 33800 V
(c) 42300 V
(d) 23900 V

136. Damper winding and pony break are the methods of starting of

(a) Slip ring motors.
(b) Synchronous motors.
(c) Schrage motors.
(d) Squirrel cage motors. [UPPCL – 2016]

137. A reactor having an inductive reactance of 4 ohm is connected to the terminals of a 120 V AC generator. Calculate the power associated with the reactor. [J&K JE 2016]

(a) 3.6 kVAR
(b) 30 kVAR
(c) 7.2 kVAR
(d) 4.16 kVAR

138. If the type of excitation of synchronous motors is critical excitation then what will be the nature of power factors? [MPJE – 2016]

(a) Lagging.
(b) Unity power factor.
(c) Lagging power factor.
(d) Leading power factor.

139. An alternator is feeding an infinite bus bar. Its prime mover is suddenly shutdown. The alternator will………

(a) Continue to work as alternator but the direction of rotation will reverse.
(b) Come to stand still.
(c) Continue to work as synchronous motor and direction of rotation will also be same.
(d) Will work as an induction motor. [J&K JE – 2016]

140. An alternator is connected to an infinite bus. If its field current is decreased then its armature current will be………

(a) Increase with zero pf lagging.
(b) Decreases with zero pf leading.
(c) Increases with zero pf leading.
(d) None of the other options.

141. A 500 MW, 3 phase star connected synchronous generator has a rated voltage of 21.5 kV at 0.85 pf. What will be the line current when operating at full load rated conditions? [LMRC AE- 2016]

(a) 13.43 KA
(b) 15.79 KA
(c) 23.25 kA
(d) 27.36 kA

142. A synchronous generator has higher power handling capacity when operating

(a) At lagging power factor.
(b) At leading power factor.
(c) At unity power factor.
(d) Independent of power factor.

143. The statement “Generators are Coherent”, implies that ……….

(a) All of them oscillate at same frequency.
(b) Each of them oscillates at different frequencies.
(c) They rotate at same frequency.
(d) Each generator rotates at different frequency.

144. Harmonics in power system are not generated by ………..

(a) Unbalanced source and balanced load.
(b) Balanced source and unbalanced load.
(c) Balanced loading with a balanced source.
(d) Non linear switches.

145. A 6 pole, 3-phase alternator running at 1000 rpm supplies to an 8-pole, 3-phase induction motor which has a rotor current of frequency 2 Hz. The speed at which the motor operates is ……….

(a) 100 rpm
(b) 970 rpm
(c) 750 rpm
(d) 720 rpm [Uttrakhand AE – 2013]

146. A 10 pole AC generator rotates at 1200 rpm. The frequency of AC voltage in cycle per second will be ……..

(a) 120
(b) 110
(c) 100
(d) 50

147. Maximum speed of a synchronous machine for 50 Hz is ………

(a) 1500 rpm
(b) 3000 rpm
(c) 20000 rpm
(d) 30000 rpm

148. We have assigned a frequency of 50 Hz to power system because it

(a) Can be easily obtained.
(b) Gives best result when used for operating both lights and machinery.
(c) Easy calculations.
(d) None

149. Direction of the alternating e.m.f. produced in the stator conductors of an alternator is given by

(a) Lenz’s law
(b) Flemings left hand rule
(c) Fleming’s right hand rule
(d) Kirchoff’s Law

150. An alternator running at 3000 rpm generates voltage at 50 Hz. The number of poles of alternator will be

(a) 8
(b) 6
(c) 4
(d) 2