301 MCQ Questions on Synchronous Machine

201. A synchronous motor is operate on no load at unity power factor, if the field current is increased, the power factor will become

(a) Leading and the stator current will decrease.
(b) Lagging and the stator current will increase.
(c) Lagging and the stator current will decrease.
(d) Leading and the stator current will increase.

202. In a synchronous motor with field under-excited the power factor will be

(a) lagging
(b) leading
(c) unity
 (d) none of these

203. In a synchronous motor the magnitude of back emf E_b depends on

(a) speed of the motor.
(b) load on the motor.
(c) both speed and stator flux.
(d) d.c. exciation only.

204. The regulation of a synchronous motor is

(a) 0.01
(b) 1
(c) 0.5
(d) 0

205. In a synchronous machine, in case the axis of field flux is in line with the armature flux then

(a) The machine is working as synchronous motor.
(b) The machine is working as synchronous generator.
(c) The machine is said to floating.
(d) The machine will vibrate violently.

206. A rotary converter generally:

(a) Combines the function of an induction motor and a dc generator.
(b) Has a set of slip rings at both ends.
(c) Has one armature and 2 fields.
(d) Is a synchronous motor and a dc generator combined.

207. A synchronous motor is supplying its rated load. If excitation is increased

(a) The power factor becomes more leading.
(b) The power factor becomes more lagging
(c) The power factor remains constant
(d) None of these.

208. Which of the following motors is preferred as a drive, when quick speed reversal is the main consideration?

(a) Wound rotor induction motor
(b) Synchronous motor
(c) Squirrel case induction motor
(d) DC Motor

209. A synchronous motor is found more economical over a load of:

(a) 2 kW
(b) 20 kW
(c) 50 kW
(d) 100 kW [UPRVUNL – 2015]

210. By reversing ……….. the direction of rotation of a synchronous motor can be reversed.

(a) supply phase sequence
(b) current to the field winding
(c) polarity of rotor poles
(d) either “polarity of rotor poles” or “supply phase sequence

211. When a synchronous motor is ……… it operates with leading power factor current.

(a) under-excited
(b) critically excited
(c) over-excited
(d) heavily loaded

212. It will be the effect on a salient pole synchronous motor if its field current is switched off (provided the motor runs at no load)?

(a) It will stop.
(b) It continues to run at synchronous speed.
(c) It continues to run at a speed slightly more than the synchronous speed.
(d) It continues to run at a speed slightly less than the synchronous speed.

213. Which of the following leads to reduction in the size of a synchronous motor?

(a) Increase in horse power rating
(b) Decrease in load angle
(c) Increase in flux density
(d) Decrease in flux density

214. On which of the following does the back emf set up in the stator of a synchronous motor depend?

1. Rotor speed
2. Rotor excitation

III. Coupling angle
Chose the correct answer from the options given below.
(a) Only II
(b) Only II and III
(c) I, II and III
(d) Only I and III [UPRVUNL – 2014]

215. A salient pole synchronous motor is running at no load. Its excitation is reduced to zero, then

(a) It will stop.
(b) It will remain running at synchronous speed.
(c) It will lose synchronism.
(d) It is uncertain. [DMRC – 2015]

216. A three phase synchronous motor will have:

(a) No slip rings.
(b) One slip ring.
(c) Two slip rings.
(d) Three slip rings. [LMRC – 2015]

217. Hunting in a synchronous motor takes place when:

(a) Supply voltage fluctuated.
(b) Load varies.
(c) Power factor is unity.
(d) Motor is under loaded. [LMRC – 2015]

218. The angle between rotating stator flux and rotor poles is called:

(a) Torque angle.
(b) Obtuse angle.
(c) Synchronizing angle.
(d) Power factor angle. [LMRC – 2015]

219. The ratio of starting torque to running torque in a synchronous motor is:

(a) 0
(b) 1
(c) 2
(d) 4 [LMRC 2015]

220. A synchronous machine is called a doubly excited machine because:

(a) It can be overexcited.
(b) It has two sets of rotor poles.
(c) Both its rotor and stator are excited.
(d) It needs twice the normal exciting current.

221. Synchronous motors are to be used in situations where

(a) The load is constant.
(b) The load is required to be driven at very high speeds.
(c) The load is to be driven at constant speed.
(d) The starting torque requirement of the load is very high.

222. When excitation of synchronous motor is increased upto normal excitation from under excitation, armature current

(a) Increases.
(b) Decreases.
(c) Remains constant.
(d) None of the above. [Uttrakhand – 2013]

223. In synchronous motor inverted V curve represents the relation between:

(a) Field current and power factor.
(b) Field current and armature current.
(c) Armature current and power factor.
(d) None of these. [MPJE – 2015]

224. ……….. motor is a constant speed motor. [UPSSSC – 2015]

(a) Synchronous motor
(b) Scharge motor
(c) Induction motor
(d) Universal motor

225. A synchronous motor is

(a) Self starting.
(b) Non self-starting.
(c) Sometimes self-starting.
(d) None of them. [UPSSSC – 2015]

226. In a synchronous motor, the minimum armature current occurs at

(a) Zero power factor.
(b) Unity power factor.
(c) Lagging power factor.
(d) Leading power factor. [MPJE – 2016]

227. When 3-phase supply is given to the stator of the motor, a

(a) Rotating field is set up.
(b) Pulsating field is set up.
(c) Revolving field at synchronous speed is set up.
(d) Rotating field at the rotor speed is set up. [MPJE – 2016]

228. A synchronous motor operated at no load with over excitation condition to draw large leading reactive current and power is called a

(a) Synchronous motor.
(b) Capacitor start motor.
(c) Synchronous condenser.
(d) None of the above. [MPJE – 2016]

229. In a synchronous machine, if the field flux is ahead of the armature field axis, in the direction of rotation, the machine works as

(a) Asynchronous motor.
(b) Asynchronous generator.
(c) Synchronous motor.
(d) Synchronous generator. [MPJE – 2016]

230. Which type of torque in synchronous motor is also called as break away torques?

(a) Starting torque.
(b) Running torque.
(c) Pull torque.
(d) Pull-out torque. [MPJE – 2016]