Practice Polyphase Induction Motors Multiple Choice Questions Quiz-1 - MCQGeeks.com

Q.1

The torque developed in the cage induction motor with auto-starter is

k/torque with direct switching
K × torque with direct switching
K2 × torque with direct switching
k2/torque with direct switching

Q.2

The efficiency of an induction motor can be expected to be nearly

60 to 90 %
80 to 90 %
95 to 98 %
99 %

Q.3

The good power factor of an induction motor can be achieved if the average flux density in the air gap is

Absent
Small
Large
Infinity

Q.4

The rotor of an induction motor runs at

Synchronous speed
Below synchronous speed
Above synchronous speed
Any of the above

Q.5

In N_s is the synchronous speed and s the slip, then actual running speed of an induction motor will be

N_s
s.N
(l-s) N_s
(N_s-l) s

Q.6

Which of the following component is usually fabricated out of silicon steel?

Bearings
Shaft
Stator core
None of the above

Q.7

The power scale of circle diagram of an induction motor can be found from

Stator resistance test
No-load test only
Short-circuit test only
None of the above

Q.8

Insertion of resistance in the rotor of an induction motor to develop a given torque

Decreases the rotor current
Increases the rotor current
Rotor current becomes zero
Rotor current remains same

Q.9

In a three-phase induction motor, the number of poles in the rotor winding is always

Zero
More than the number of poles in stator
Less than number of poles in stator
Equal to number of poles in stator

Q.10

Which type of bearing is provided in small induction motors to support the rotor shaft?

Ball bearings
Cast iron bearings
Bush bearings
None of the above

Q.11

The vafcie of transformation ratio of an induction motor can be found by

Open-circuit test only
Short-circuit test only
Stator resistance test
None of the above

Q.12

An induction motor can run at synchronous speed when

It is run on load
It is run in reverse direction
It is run on voltage higher than the rated voltage
e.m.f. is injected in the rotor circuit

Q.13

The torque of an induction motor is

Directly proportional to slip
Inversely proportional to slip
Proportional to the square of the slip
None of the above

Q.14

The 'crawling' in an induction motor is caused by

High loads
Low voltage supply
Improper design of machine
Harmonics developed in the motor

Q.15

5 H.P., 50Hz, 3-phase, 440 V, induction motors are available for the following r.p.m. Which motor will be the costliest?

730 r.p.m.
960 r.p.m.
1440 r.p.m.
2880 r.p.m.

Q.16

In the squirrel-cage induction motor the rotor slots are usually given slight skew

To reduce the magnetic hum and locking tendency of the rotor
To increase the tensile strength of the rotor bars
To ensure easy fabrication
None of the above

Q.17

A squirrel cage induction motor is not selected when

Initial cost is the main consideration
Maintenance cost is to be kept low
Higher starting torque is the main consideration
All above considerations are involved

Q.18

The purpose of using short-circuit gear is

To short circuit the rotor at slip rings
To short circuit the starting resistances in the starter
To short circuit the stator phase of motor to form star
None of the above

Q.19

Insertion of reactance in the rotor circuit

Reduces starting torque as well as maximum torque
Increases starting torque as well as maximum torque
Increases starting torque but maximum torque remains unchanged
Increases starting torque but maximum torque decreases

Q.20

The maximum torque in an induction motor depends on

Frequency
Rotor inductive reactance
Square of supply voltage
All of the above

0 h : 0 m : 1 s