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Objective questions and answers or MCQ of Electrical Machines page-18


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281. In the Q. 280, what will be the primary rated voltage of the transformer?

a) 33,000 V
b) 1650 V
c) 16,500 V
d) 1500 V

Ans: (c)

282. The speed-torque characteristics for single-phase induction motor shown below are for

a) Shaded pole motor
b) Split phase motor
c) Capacitor-start motor
d) Repulsion-start run motor

Ans: (c)

283. The induced e.m.f. in one phase of the rotor winding is 120 V when the rotor is blocked and, the resistance and reactance per phase of stator winding are 0.2 Ω and 0.3 Ω respectively. What will be the rotor current?

a) 330 A
b) 332 A
c) 250 A
d) 200 A

Ans: (b)

284. A circuit for the auto transformer is shown below. The point b is located half way between terminals a and c. The resistance of entire winding is 0.1 ohm, and the resistance of the position bc is 0.40 ohm. What will be the copper loss at an output of 10 A when the exciting current is neglected?

a) Watts
b) 2.5 Watts
c) 10 Watts
d) 4 Watts

Ans: (b)

285. In the figure of Q. 284, if the reactance of part ab is 0.2 ohm and that of common part is 0.1 ohm, what will be the input current if primary voltage is 20 V?

a) 60 A
b) 33.3 A
c) 63.3 A
d) 30 A

Ans: (c)

286. What will wattmeter indicate is connected across supply line in the figure of Q. 284, provided V1 = 20 V and reactance of ab is 0.2 ohm, reactance of common part is 0.1 ohm and the core loss is neglected

a) 200 Watts
b) 100 Watts
c) 500 Watts
d) 400 Watts

Ans: (d)

287. A series motor has 2 poles and 95 turns per pole. The resistance of 2 field coils connected in series is 3.02 ohms. The voltage drop across the field is 62 V and current is 3.55 A at 60 Hz. What will be the field reactance?

a) 27 ohms
b) 60 ohms
c) 17.2 ohms
d) 68 ohms

Ans: (c)

288. The armature winding of repulsion motor is excited

a) Conductively
b) Inductively
c) Resistively
d) None of the above

Ans: (b)

289. The armature winding of series motor is excited

a) Conductively
b) Inductively
c) Resistively
d) None of the above

Ans: (a)

290. Which of the following parameters contributes to the friction loss in the alternators?

a) Temperature
b) Lubrication of bearings
c) Load variation
d) Velocity of the shaft
e) All above parameters

Ans: (e)

291. The difference between input and I2Rloss will give the

a) Friction loss
b) Windage loss
c) Core loss
d) Sum of (a), (b) and (c)

Ans: (d)

292. The friction, winding and core losses of alternator can easily be determined by

a) Running the alternator at synchronous speed
b) Running the alternator as a synchronous motor at rated speed at full load
c) Running the alternator as a synchronous motor at rated speed at no load
d) None of the above

Ans: (c)

293. The eddy-current loss in the alternator will be minimum if the air gap

a) Between poles and the slots of the armature is large compared to width of the slot
b) Between poles and the slots of the armature is minimum compared to width of the slot
c) Does not exist
d) None of the above

Ans: (a)

294. Eddy current losses in the alternator are

a) Dependent on the load
b) Independent of the load
c) Dependent on the excitation
d) (b) and (c) both
e) None of the above

Ans: (d)

295. The skewing of the rotor bars of the induction motor

a) Will reduce the induced voltage in each bar to a value less than if the base were unskewed
b) Will increase the induced voltage in each bar to a value more than if the bars were unskewed
c) Increases the cogging
d) Increases the motor noise

Ans: (a)


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