12- The rotor slots are slightly skewed in squirrel cage induction motor to
(A) increase the strength of rotor bars
(B) reduce the magnetic hum and locking tendency of rotor
(C) economize on the copper to be used
(D) provide ease of fabrication
13- Slip test in a synchronous machine is performed to determine
(A) slip
(B) direct axis reactance and quadrature axis reactance
(C) positive sequence reactance and negative sequence reactance
(D) sub-transient reactance
14- An induction motor and synchronous motor are connected to a common feeder line. To operate the feeder line at unity pf, the synchronous motor should be
(A) under excited
(B) overexcited
(C) normally excited
(D) disconnected from the common terminals
15- In a synchronous motor, the synchronizing power comes into action when
(A) rotor speed either exceeds or falls below the synchronous speed
(B) rotor speed is equal to synchronous speed
(C) rotor speed falls below the synchronous speed
(D) rotor speed exceeds the synchronous speed
16- Asynchronous motor is operating on no-load at unity power factor. If the field current is increased, the power factor will become
(A) leading and the current will decrease
(B) lagging and the current will increase
(C) lagging and the current will decrease
(D) leading and the current will increase
17- The mmf produced by the current of 3-phase induction motor
(A) rotates at the speed of rotor in the air gap
(B) is standstill with respect to stator mmf
(C) rotates at slip speed with respect to stator mmf
(D) rotates at synchronous speed with respect to rotor
18- An induction motor when started on load does not accelerate upto full speed but runs at 1/7th of rated speed. The motor is said to be
(A) locking
(B) plugging
(C) crawling
(D) cogging
19- For the protection of a large squirrel cage induction motor against single phase, normally
(A) an over current relay is used
(B) a differential relay is used
(C) a directional relay is used
(D) negative sequence current relay is used
20- In a single phase shaded pole squirrel cage induction motor, the flux in the shaded part always
(A) leads the flux in the unshaded pole segment
(B) is in phase with the flux in the unshaded pole segment
(C) lags the flux in the unshaded pole segment
(D) is 180 out of phase with the unshaded pole segment
21- Hunting in a synchronous motor takes place when the
(A) Friction in the bearings is more
(B) Air gap is less
(C) Load is variable
(D) Load is constant
22- In the star-delta starter of an induction motor,
(A) Applied voltage per stator phase is 67.7% of the line voltage
(B) Applied voltage per stator phase is 37.4% of the line voltage
(C) Applied voltage per stator phase is 70.7% of the line voltage
(D) Applied voltage per stator phase is 57.7% of the line voltage.
ANSWERS:
12-(B), 13-(B), 14-(B), 15-(A), 16-(D), 17-(B), 18-(C), 19-(D), 20-(C), 21-(C), 22-(D)