Multiple Choice Questions on AC Motors
1- A synchronous motor can develop synchronous torque
(A) when under loaded
(B) when overexcited
(C) only at synchronous speed
(D) below or above the synchronous speed
2- In case of AC motor circuit, static frequency changers are used for
(A) power factor improvement
(B) improvement in cooling
(C) reversal of direction of rotation
(D) speed regulation
3- A wound rotor induction motor is preferred over a squirrel cage induction motor, when the major/consideration/considerations is/are
(A) large starting torque
(B) low starting current
(C) speed control for limited range
(D) all of the above
4- The motor commonly used in computers and digital systems is
(A) DC shunt motor
(B) induction motor
(C) synchronous motor
(D) reluctance motor
5- When an induction motor is switched on, the rotor frequency is
(A) zero
(B) 60 Hz
(C) same as slip frequency
(D) same as supply frequency
6- In an induction motor, if the air gap is increased, its
(A) speed will reduce
(B) power factor will decrease
(C) efficiency will improve
(D) speed will increase
7- The power input in a blocked rotor test performed on 3-phase induction motor is approximately equal to
(A) iron loss in the core
(B) hysteresis loss in the core
(C) eddy current loss in the core
(D) copper loss in the windings
8- The type of single phase induction motor having the highest power factor at full load is
(A) shaded pole type
(B) split phase type
(C) capacitor start type
(D) capacitor run type
9- In a double squirrel cage induction motor, the outer cage winding has
(A) high inductance
(B) low resistance
(C) high resistance
(D) high capacitance
10- In a 3-phase induction motor, the torque developed is maximum when the rotor circuit resistance per phase is equal to
(A) rotor leakage reactance per phase at standstill
(B) slip times the rotor leakage reactance per phase at standstill
(C) stator resistance per phase
(D) stator leakage reactance per phase
11- If the field of a synchronous motor is under excited, the power factor will be
(A) lagging
(B) leading
(C) unity
(D) depending upon the type of synchronous motor
ANSWERS:
1-(C), 2-(D), 3-(D), 4-(B), 5-(D), 6-(B), 7-(D), 8-(D), 9-(C), 10-(B), 11-(A)