1. The given figure shows typical torque-speed curves of the following induction motors:
List-I
A. Ordinary cage
B. Double cage
C. Deep bar rotor
D. Slip ring motor
List-II
The correct matching of the motors and torque-speed curves is
(a) A-2 B-3 C-4 D-1
(b) A-3 B-2 C-1 D-4
(c) A-4 B-2 C-1 D-3
(d) A-4 B-3 C-2 D-1
Answer: (d) A-4 B-3 C-2 D-1
2. Which one of the following relations between starting torque ‘Ts‘ and maximum torque ‘Tmax’ is correct? (‘a’ is the ratio of rotor resistance to standstill rotor reactance)
Answer: (c)
3. A 6-pole, 50 Hz, 3-φ induction motor is running at 950 rpm and has rotor copper loss of 5 kW. Its rotor input is …….. kW.
(a) 100
(c) 95
(b) 10
(d) 5.3
Answer: (a) 100
4. In a V/f controlled 4-pole induction motor which runs at 50 Hz and rated voltage, the speed was found to be 1440 rpm. If the machine runs at 30 Hz, what is the slip?
(a) 0.03
(b) 0.06
(c) 0.04
(d) 0.0556
Answer: (b) 0.06
5. A wound rotor induction motor runs with a slip of 0.05 when developing full load torque. Its rotor resistance is 0.45Ω per phase. If an external resistance of 0.505Ω per phase is connected across the slip rings. What is the slip of full load torque?
(a) 0.03
(c) 0.09
(b) 0.06
(d) 0.1 [UPPCL JE 2014]
Answer: (d)
6. The emf induced in a coil of N turns is given by
Answer: (b)
7. The frequency of rotor emf of an 4-pole induction motor is 2 Hz. If the supply frequency is 50 Hz, then the motor speed is
(a) 1500 rpm
(b) 750 rpm
(c) 1440 rpm
(d) 720 rpm [UPPCL AE – 2016]
Answer: (c) 1440 rpm
8. Which one of the following equation shows the relation between torque, slip and voltage for an induction motor if the symbols have their usual meanings? [UPPCL – 2016]
Answer: (a)
9. For a slip ring induction motor, if the supply voltage changes by 5% it will produce approximately a change of… in rotor torque. [JUVNL JE 2017]
(a) 10%
(b) 21%
(c) 5%
(d) 15%
Answer: (a) 10%
10. A four pole three phase induction motor is running at 4 percent slip at full load. If the speed of motor be 720 rpm, the supply frequency is:
(a) 16 Hz
(b) 25 Hz
(c) 30 Hz
(d) 50 Hz [J&K JE 2016]
Answer: (b) 25 Hz
11. The following figure represents:
(a) 3-phase squirrel cage induction motor
(b) 3-phase slip ring induction motor
(c) 3-phase synchronous motor
(d) 3-phase transformer
Answer: (b) 3-phase slip ring induction motor
12. A three phase squirrel cage induction motor of rating 4 pole, 3-phase, 50Hz, 5 kW, runs at a speed of 1440 rpm. The frequency of the rotor current is:
(a) 49 Hz
(b) 2 Hz
(c) 50 Hz
(d) 51 Hz
Answer: (b) 2 Hz
13. A 6-pole, 50Hz, 3-phase induction motor has rotor resistance of 0.25 ohm and develops the maximum torque at 875 rpm. The rotor reactance and slip at the maximum torque respectively are:
(a) 2, 0.125 pu
(b) 2, 0.25 pu
(c) 1, 0.25 pu
(d) 1, 0.125
Answer: (c) 1, 0.25 pu
14. If load torque is proportional to square of speed, then what will be the characteristics curve of load torque Vs speed?
Answer: (c)
15. A 3 phase, 50 Hz induction motor draws 50 kW from the mains. If the stator losses are 2 kW and rotor emf oscillates at 100 oscillations per minute the rotor copper losses will be:
(a) 1.8 kW
(b) 1.2 kW
(c) 1.9 kW
(d) 1.6 kW
Answer: (d) 1.6 kW
