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Objective questions and answers or MCQ of Electrical Machines page-19


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296. Which of the following motors have almost constant speed over their full load range?

a) DC series motors
b) AC series motors
c) DC shunt motors
d) Low resistance squirrel cage motors
e) (c) and (d) both

Ans: (e)

297. If two wound-rotor induction motors are arranged so that the stator of one is connected to an external source and its rotor output is connected to the other, what will be the input conditions for the other induction motor?

a) The second motor will run at its own slip but at voltage of first motor
b) The second motor will run at slip frequency and voltage of first motor
c) The second motor will run
d) The second motor will act as frequency converter

Ans: (b)

298. In the Q. 297, the first motor acts as

a) Voltage converter
b) Frequency converter
c) Current converter
d) Power converter

Ans: (b)

299. In the Q. 297, the slip frequency of the second motor

a) Is the difference between its applied frequency and its frequency of rotation
b) Is the difference between of slip-frequency first motor and its frequency of rotation
c) (a) or (b)
d) None of the above

Ans: (c)

300. Four speed-torque curves are shown below, which of the curve is drawn for repulsion start induction run

a) A
b) B
c) C
d) D

Ans: (a)

301. The torque developed in D.C motor depends on

a) Armature Current
b) Magnetic field
c) Magnetic field and Magnetic Current
d) Speed

Ans: (c)

302. The speed regulation of D.C. motor can be ideally achieved with

a) Variable excitation to the field of the motor
b) Constant excitation to the field of the motor
c) A.C. excitation to the field of the motor
d) No excitation to the field of the motor

Ans: (b)

303. If the excitation to the field of the D.C. motor is constant then the torque developed in the motor is proportional to

a) Armature current
b) Field current
c) Speed
d) Magnetic flux

Ans: (a)

304. For which of the following machine residual magnetism is a requirement to build up voltage output?

a) Separately excited generator
b) Self-excited generator
c) All A.C. generators
d) None of them

Ans: (b)

305. What will happen to the d.c. generator if the field winding attains the critical resistance?

a) It will generate maximum voltage
b) It will generate maximum power
c) It will not develop voltage at all
d) None of them

Ans: (c)

306. Which of the following conditions hold true for paralleling two d.c. generators ?

a) Their polarities must match
b) Their phase sequence must match
c) Their polarities and voltages must match
d) (b) and (c) both

Ans: (c)

307. The armature voltage control is suitable if the d.c. machine is driven at

a) Constant current
b) Constant torque
c) Constant speed
d) Constant magnetic field

Ans: (b)

308. Which of the following parameter to achieve the variable speed of d.c. drive ?

a) Magnetic field
b) Armature resistance
c) Voltage
d) None of the above

Ans: (c)

309. The Ward Leonard method of speed control of d.c. machin controls the speed below or above normal speed in clockwise and anti-clockwise directive.

a) True
b) False

Ans: (a)

310. Which of the following motor one will choose to drive the rotory compressor?

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

Ans: (b)


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