Deck 7: Contactors, Motors, and Load Torques

Question 1

The number of operations per hour in case of class IV contactor will be around

A)100
B)600
C)900
D)1200.

Answer 1

1200.

Question 2

In case of contactors, the duty in which the main contacts remain closed for a period bearing a definition relation to the no-load periods, is known as

A)Standard duty
B)Intermittent duty
C)Temporary duty
D)Un-interrupted duty.

Answer 2

Intermittent duty

Question 3

In case of contactors the ratio of the in service period to the entire period, expressed as a percentage is known as

A)duty
B)load factor
C)class of contact
D)none of the above.

Answer 3

load factor

Question 4

A class I contactor should be mechanically sound to withstand

A)0.05 million times
B)0.25 million times
C)1.2 million times
D)5.0 million times.

Question 5

Which of the following pair is used for frequency converters ?

A)Squirrel cage induction motor and synchronous motor
B)Wound rotor induction motor and synchronous motor
C)Wound rotor induction motor and squirrel cage induction motor

Question 6

Belted wound rotor induction motors are preferred for

A)machine tools
B)gyratory crushers
C)belt conveyor
D)water pumps.

Question 7

The cooling time constant is usually

A)equal to the heating time constant
B)more than heating time constant
C)none of these.
D)all of the above

Question 8

A motor of less than full load power rating can be used if the load is

A)continuous duty
B)short time duty
C)intermittent periodic duty
D)none of these.

Question 9

Pole changing method of speed control is used in

A)slip ring induction motor
B)dc shunt motor
C)dc series motor
D)squirrel cage induction motor.

Question 10

To save the energy during braking

A)dynamic braking is used
B)plugging is used
C)regenerative braking is used
D)mechanical braking is used.

Question 11

To get speed higher than the base speed of the dc shunt motor

A)armature resistance control is used
B)field resistance control is used
C)armature voltage control is used
D)none of these.

Question 12

Rotor resistance speed control is used in

A)squirrel cage induction motor
B)synchronous motor
C)slip ring induction motor
D)dc shunt motor.

Question 13

Effect of friction torque is more pronounced

A)when the drive is running on full speed
B)when the drive is being started
C)when the drive is being stopped
D)when the drive at half of its normal speed.

Question 14

The equilibrium speed of a motor load system is obtained

A)when motor torque equals the load torque
B)when motor torque is less than the load torque
C)when motor torque is more than the load torque
D)none of the these.

Question 15

Most commonly used ac motor is

A)Synchronous motor
B)Slip ring induction motor
C)Squirrel cage induction motor
D)ac commutator induction motor.

Question 16

The motor commonly used in computers and digital systems is

A)dc shunt motor
B)Induction motor
C)Stepper motor
D)Synchronous motor.

Question 17

Regenerative braking mode can be achieved in which quadrant (V-I curve)?

A)Third
B)Second
C)Fourth
D)First

Question 18

Fan type of loads exhibits which type of load torque characteristics?

A)Constant torque characteristics
B)Linearly rising torque characteristics
C)Non-Linearly rising torque characteristics
D)Non-Linearly decreasing torque characteristics

Question 19

Type-A chopper is used for obtaining which type of mode?

A)Motoring mode
B)Regenerative braking mode
C)Reverse motoring mode
D)Reverse regenerative braking mode

Question 20

Boost converter is used to _________

A)Step down the voltage
B)Step up the voltage
C)Equalize the voltage
D)Step up and step down the voltage

Question 21

Reverse motoring mode is available in fourth quadrant.

A)True
B)False
C)none
D)all of the above

Question 22

Which one is an example of variable loss?

A)Windage loss
B)Hysteresis loss
C)Armature copper loss
D)Friction loss

Question 23

Load torques can be classified into how many types?

A)Three
B)Two
C)Four
D)Five

Question 24

Rolling mills exhibit what type of load torque characteristics?

A)Constant torque characteristics
B)Linearly rising torque characteristics
C)Non-Linearly rising torque characteristics
D)Non-Linearly decreasing torque characteristics

Question 25

What is the relationship between torque and speed in constant type loads?

A)Torque is independent of speed
B)Torque linearly increases with increase in speed
C)Torque non-linearly increases with an increase in speed
D)Torque non-linearly decreases with an increase in speed