Electrical Machines solved Questions-Gate 2016

MCQ 4.1 The slip of an induction motor normally does not depend on

(A) rotor speed (B) synchronous speed

(C) shaft torque (D) core-loss component

MCQ 4.2 A 220 V, 15 kW, 100 rpm shunt motor with armature resistance of 0.25 Ω,

has a rated line current of 68 A and a rated field current of 2.2 A. The

change in field flux required to obtain a speed of 1600 rpm while drawing a

line current of 52.8 A and a field current of 1.8 A is

(A) 18.18% increase (B) 18.18% decrease

(C) 36.36% increase (D) 36.36% decrease

MCQ 4.3 The locked rotor current in a 3-phase, star connected 15 kW, 4 pole, 230 V, 50 Hz induction motor at rated conditions is 50 A. Neglecting losses and magnetizing current, the approximate locked rotor line current drawn when the motor is connected to a 236 V, 57 Hz supply is

(A) 58.5 A (B) 45.0 A

(C) 42.7 A (D) 55.6 A

MCQ 4.4 A single phase 10 kVA, 50 Hz transformer with 1 kV primary winding draws 0.5 A and 55W, at rated voltage and frequency, on no load. A second transformer has a core with all its linear dimensions 2 times the corresponding dimensions of the first transformer. The core material and lamination thickness are the same in both transformer. The primary winding of both the transformers have the save number of turns. If a rate voltage of 2 kV at 50 Hz is applied to the primary of the second transformer, then the no load current and power, respectively, are

(A) 0.7 A, 77.8 A (B) 0.7 A, 155.6W

(C) 1A, 110W (D) 1A, 220W

MCQ 4.5 A 4 point starter is used to start and control the speed of a

(A) dc shunt motor with armature resistance control

(B) dc shunt motor with field weakening control

(C) dc series motor

(D) dc compound motor

                                                                      ANSWERS

Answers will be updated soon....