Electrical Engineering Question Answers- Feb 2018

Question No. 1. The d.c. series motor should always be started with load because
(A) at no load, it will rotate at dangerously high speed.
(B) it will fail to start.
(C) it will not develop high starting torque.
(D) all are true.
 Ans: A

Question No. 2. The armature of a dc machine is laminated to reduce:
(A) Eddy current loss
(B) Hysteresis loss
(C) copper losses
(D) friction and windage losses
 Ans: A

Question No. 3. The frequency of the rotor current in a 3 phase 50 Hz, 4 pole induction motor at full
load speed is about
(A) 50 Hz.
(B) 20 Hz.
(C) 2 Hz.
(D) Zero.
 Ans: C

Question No. 4. If a single phase alternator has 8 slots per pole uniformly speed, but the winding is arranged with the middle two left empty, the breadth coefficient will be

(A) 0.53.
(B) 0.88

(C) 0.67
(D) 0.99
Answer: (A) 0.53.

Question No. 5. In DC generators, armature reaction is produced actually by
 (A) Its field current. (B) Armature conductors.
 (C) Field pole winding. (D) Load current in armature.
Ans: D

Question No. 6. A synchronous motor is operating on no-load at unity power factor. If the field
 current is increased, power factor will become
(A) Leading & current will decrease
(B) Lagging & current will increase.
(C) Lagging & current will decrease.
(D) Leading & current will increase.
Ans: A

Question No. 7. An a.c. tachometer is just a ________with one phase excited from the carrier
(A) two-phase A.C. servomotor (B) two-phase induction motor
(C) A.C. operated universal motor (D) hybrid stepper motor.
Ans: D

Question No. 8. Oil-filled cable has a working stress of __________ kV/mm
(A) 10 (B) 12
 (C) 13 (D) 15
 Ans: D
 This is defined by dielectric strength of mineral oil i.e. 15 kV/mm.

Question No.9. Which relays comes into operation in the event of the failure of prime mover connected to ihe generator ?
(A) Buchholz relay
(B) Differential relay
(C) Reverse power relay
(D) None of the above.

Answer; (C) Reverse power relay

A ceiling fan uses
 (A) split-phase motor.
(B) capacitor start and capacitor run motor.
(C) universal motor.
(D) capacitor start motor.
Ans: D
 To give starting torque and to maintain speed.

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