301 MCQ Questions on Induction Motors

151. At what angle difference is the main winding and the start winding separated in a split phase capacitor start induction motor? [UPPCL JE – 2018]

(a) 30° mechanical
(b) 90° electrical
(c) 45° electrical
(d) 45° mechanical

152. The bearings used to support the rotor shafts are generally

(a) Ball bearings
(b) Bush bearings
(c) Magnetic bearings
(d) Needle bearings

153. Which of the following can be obtained by equivalent circuit of an induction machine?

(a) Complete performance characteristics of the machine
(b) Temperature rise in the core
(c) Type of protection used in the machine
(d) Design parameters of the winding

154. Number of phases used for a load above 4 kW is:

(a) 1
(b) 2
(c) 3
(d) 4 [UPPCL – 2016]

155. In an induction motor, if stator’s electrical speed is denoted by N_s, and rotor’s mechanical speed is denoted by N_r, then what will be the slip? [UPPCL – 2016]

(a) (N_s – N_r)/2
(b) (N_r – N_s)/2
(c) (N_s – N_r)/N_r
(d) (N_s – N_r)/N_s

156. A small….. in poly phase induction motor helps to reduce the magnetizing current. [UPPCL 2016]

(a) Alter gap
(b) Yoke
(c) Air gap
(d) Insulator

157. A 3-phase induction motor when started picks up speed but runs stably at about half the normal speed. This is because of

(a) Unbalance in the supply voltages
(b) Non-sinusoidal nature of the supply voltage
(c) Stator circuit asymmetry
(d) Rotor circuit asymmetry

158. Which one of the following statement is not true about 3-phase induction motor?

(a) Self-starting
(b) Less armature reaction and brush sparking because of the absence of commutators and brushes that may cause sparks
(c) Robust in construction.
(d) Require an external device to start

159. In an induction motor, at speed near to synchronous speed, the torque speed and torque-slip curves are approximately:

(a) Hyperbola
(b) Parabola
(c) Ellipses
(d) Straight lines [UPPCL – 2016]

160. If rotor resistance in an induction motor is small, rotor current will be:

(a) Zero
(b) Low
(c) Large
(d) Infinite [UPPCL – 2016]

161. Star connection is used for the motors up to:

(a) 5 HP
(b) 10 HP
(c) 3 HP
(d) 12 HP [UPPCL – 2016]

162. Slip of an induction motor…… when the rotor starts gaining speed:

(a) Remains same
(b) Increases
(c) Decreases
(d) Increases or decreases [UPPCL – 2016]

163. In a capacitor start motor, the phase displacement starting and running winding can be nearly (in degrees):

(a) 10
(b) 30
(c) 60
(d) 90 [ESIC JE – 2016]

164. As compared to D.O.L. starter, Star Delta starter operates at:

(a) full voltage
(b) 72% of full voltage
(c) 58% of full voltage
(d) 34% of full voltage [UPPCL – 2016]

165. For induction motors at low values of slip:

(a) The torque slip is approximately a hyperbola
(b) The torque slip is approximately a straight line
(c) The torque slip curve is at its maximum
(d) The torque slip curve is approximately a parabola [UPPCL – 2016]

166. Low HP AC induction motors have:

(a) HRC fuse
(b) Thermal over load relays
(c) HRC fuse and thermal overload relays
(d) Bimetallic relays [UPPCL – 2016]

167. The advantages of 3- φ induction motor are:

(a) All of the other options
(b) Very simple and extremely rugged
(c) Minimum maintenance
(d) Low cost and high efficiency [UPPCL – 2016]

168. For slip ring induction motors:

(a) Maximum torque is constant
(b) Maximum torque is not related to slip
(c) Maximum torque is proportional to slip
(d) Maximum torque is inversely proportional to slip

169. For an induction motor the torque is proportional to the product of

(a) Current and power factor of the motor
(b) Current and impedance of the motor
(c) flux and current
(d) Current and power factor of the motor and flux

170. A capacitor-start single phase induction motor is switched on to supply with its capacitor replaced by an inductor of equivalent reactance value. It will:

(a) Start and then stop
(b) Start and run slowly
(c) Start and run at a rated speed
(d) Not start at all

171. What does happen if tripled harmonics given to induction motor?

(a) Will results in short circuit
(b) Fail to start
(c) Nothing will happen
(d) None of the above [UPJN AE – 2016]

172. The output indicate on the name plate of any motor is always the:

(a) Power drawn in kW
(b) Power drawn in KVA
(c) Output power at the shaft
(d) None of the above

173. In a capacitor-start single phase motor, when capacitor is replaced by a resistance?

(a) Torque will increase
(b) The motor will consume less power
(c) Motor will run in reverse direction
(d) Motor will continue to run in same direction

174. Which starting method is not used in squirrel cage induction motors?

(a) Resistance in rotor circuit
(b) Resistance in stator circuit
(c) Auto-transformer starting
(d) Star delta starting

175. A 30, 460V, 100-hp, 60Hz, 6-pole induction machine delivers rated output power at a slip of 0.05. What is the speed of the rotating air gap field?

(a) 90 rpm
(b) 1710 rpm
(c) 1800 rpm
(d) 1200 rpm

176. What is synchronous wattage in an induction motor? [JUVNL JE – 2017]

(a) Combined stator and rotor input in watts
(b) Shaft output in watts
(c) Stator input in watts
(d) Rotor input in watts

177. The direction of rotation of an ordinary shaded pole single phase induction motor:

(a) Can be reversed by reversing the supply terminal connections to the stator winding
(b) Cannot be reversed
(c) Can be reversed by open-circuiting the shading ring
(d) Can be reversed by short-circuiting the shading ring

178. The rotor of an induction motor cannot run at synchronous speed because:

(a) Stator flux would then become zero.
(b) Losses would increase
(c) Rotor torque would then become zero
(d) Induction rotor would then become synchronous motor.

179. According to double field revolving theory, the rotor of a single phase induction motor may be visualized as:

(a) Two rotors running in opposite direction with different stator windings
(b) Two rotors running in same direction with common stator winding
(c) Two rotors running in same direction with different stator winding
(d) Two rotors running in opposite direction with a common stator winding

180. In direct on line starter, no volt release is to:

(a) Safe guard against supply fluctuations
(b) Safe guard the motor against sudden failure of supply
(c) Safe guard against over load
(d) Safe guard against earth faults

181. The motor used in electric traction is

(a) DC shunt motor
(b) Single phase induction
(c) Three phase induction motor
(d) Synchronous motor

182. To avoid cogging in induction motor, the number of rotor slots should not be …………. of rotor slots.

(a) Greater than
 (b) Dependent on
(c) Equal to the number
(d) Less than

183. In both squirrel cage and slip ring induction motors, number of poles on stator is:

(a) Independent of rotor
(b) Less than that of rotor
(c) Same as that of rotor
(d) More than that of rotor

184. Rotor of an induction motor always runs at:

(a) More than synchronous speed
(b) Any speed as required
(c) Synchronous speed
(d) Less than synchronous speed

185. The standard rating HP of an induction motor is equivalent to:

(a) 374.5 watts
(b) 753.5 watts
(c) 573.5 watts
(d) 735.5 watts

186. The starting torque of a single phase induction motor is

(a) Uniform
(b) High
(c) Low
(d) Zero

187. An external resistance can only be added to the rotor circuit of a:

(a) Phase wound rotor or slip ring induction motor
(b) Single phase squirrel cage induction motor
(c) Single phase slip ring induction motor
(d) 3 phase squirrel cage induction motor

188. A three phase 50 Hz, 440 V, Induction motor has a speed of 950 rpm. If the machine has 6 poles, the percentage slip would be:

(a) 10%
(b) 5%
(c) 1%
(d) 0.5%

189. For a 50Hz, power supply, the maximum speed of an Induction motor can not be:

(a) 960 rpm
(b) 1440 rpm
(c) 3000 rpm
(d) 500 rpm [UJVNL – 2016]

190. Starting torque can be obtained in the case of a single phase induction motor with identical main and auxiliary winding by connecting:

(a) A capacitor across the mains
(b) A capacitor in series with the machine
(c) A Capacitor in series with the auxiliary winding
(d) Equal value capacitors in series with the main and the auxiliary windings

191. A 3 phase, 440V, 50 Hz, induction motor has slip of 3%. The frequency of rotor emf will be:

(a) 150 Hz
(b) 15 Hz
(c) 3 Hz
(d) 1.5 Hz

192. Full load current of an induction motor is 20A the expected no load current may be:

(a) 25 A
(b) 15 A to 18 A
(c) 11 A to 14 A
(d) 6 A to 10 A

193. Various methods for starting a 3 phase, induction motor are given which method will required six stator terminal:

(a) DOL
(b) Auto transformer
(c) Star-Delta
(d) Rheostat

194. The stator of a 3 phase, 10 pole induction motor possesses 120 slots. If a lap winding is used, calculate the coil pitch, if the coil width extends from slot 1 to slot 11.

(a) 72.12%
(b) 83.30%
(c) 12%
 (d) 42%

195. A 0.5 HP, 6 pole wound rotor induction motor is excited by a 3-phase 60 Hz source. Calculate the frequency of the rotor current at standstill.

(a) 50Hz
(b) 30Hz
(c) 60Hz
(d) 120Hz

196. The usual value of slip of a 3φ  induction motor at full load is about

(a) 0.05
(b) 0.1
(c) 0.3
(d) 0.8 [J&K JE – 2016]

197. During starting of induction motor at the terminals of the machine

(a) There is a current in rush
(b) There is a dip in voltage
(c) There is combination of both of current and voltage dip
(d) None of the other options

198. In a 3-phase induction motor, a deep bar rotor is used for obtaining

(a) More starting torque
(b) Reduced rotor loss
(c) More pull out torque
(d) More starting speed

199. In an induction motor the slip power recovery schemes can be used

(a) In constant power drive only
(b) In constant torque drive only
(c) In both constant power and constant torque drives
(d) None of the other options

200. In electrical braking of three phase induction motor for the condition when the motor speed is greater than its synchronous speed the ……… braking technique may be used.

(a) Regenerative
(b) Dynamic
(c) Plugging
(d) None of the other options