1). In V/F speed control of 3-phase induction motor, with increase in frequency, the slip at which maximum torque occurs.

a)
increase

b)
decrease

c)
either of these

d)
Non of the above

2). In star-delta starting of squirrel cage induction motor compared to DOL starting the starting current and torque are

a)
1/√3,1/3

b)
1/3,1/3

c)
1/√3,1/√3

d)
1/3,1/√3

3). An induction motor has synchronous speed of 1500 rpm. what will be the slip when it is running on a speed of 1450 rpm?

a)
+3.33%

b)
-3.33%

c)
+3%

d)
-3%

4). A 4 pole, 3- induction motor is running at 4% slip at full load. if the speed of the motor is 720 rpm, the supply frequency is

a)
50 Hz

b)
60 Hz

c)
25 Hz

d)
40 Hz

5). For the purpose of starting an induction motor, star/delta switch is an equivalent to auto transformer of ratio

a)
33.3%

b)
66.3%

c)
50%

d)
57.7%

6). For satisfactory performance of 3-phase 480V, 60 Hz induction motor, the supply voltage at 50 Hz should be equal to

a)
480 V

b)
400 V

c)
420 V

d)
350 V

7). In a 3- phase induction motor, if the supply voltage and frequency are reduced by the same ratio, then slip at which maximum torque occurs is

a)
more and maximum torque remains constant

b)
more and maximum torque decreases

c)
less and maximum torque decreases

d)
less and maximum torque increases

8). To control the speed of an induction motor, the supply frequency is reduced by 10%. for the same magnetizing current to remain constant, the supply voltage must be

a)
Reduced by 10%

b)
Reduced by 20%

c)
Increased by 10%

d)
Increased by 20%

9). In V/f control of 3-
phase induction motor, with increase in frequency, the slip at which maximum torque occurs

a)
Increase

b)
decrease

c)
either of these

d)
non of the above

10). Rotor resistance speed control is used in

a)
squirrel cage induction motor

b)
slip ring induction motor

c)
dc shunt motor

d)
synchronous motor