Deck 6: Transformer and D.C Motor

Question 1

An open-circuit test on a transformer is conducted primarily to measure

A)insulation resistance
B)copper loss
C)core loss
D)total loss

Answer 1

core loss

Question 2

A no-load test is performed on a transformer to determine

A)core loss
B)copper loss
C)efficiency
D)magnetising current and loss

Answer 2

magnetising current and loss

Question 3

The voltage transformation ratio of a transformer is equal to the ratio of

A)primary turns to secondary turns
B)secondary current to primary current
C)secondary induced e.m.f. to primary induced e.m.f.
D)secondary terminal voltage to primary applied voltage

Answer 3

secondary induced e.m.f. to primary induced e.m.f.

Question 4

Part of the transformer which is most subject to damage from overheating is

A)iron core
B)copper winding
C)winding insulation
D)frame or case

Question 5

If a transformer is switched on to a voltage more than the rated voltage

A)its power factor will deteriorate
B)its power factor will increase
C)its power factor will remain unaffected
D)its power factor will be zero

Question 6

Auto-transformer makes effective saving on copper and copper losses, whenits transformation ratio is

A)approximately equal to one
B)less than one
C)great than one
D)none of the above

Question 7

Minimum voltage regulation occurs when the power factor of the load is

A)unity
B)lagging
C)leading
D)zero

Question 8

In a step-down transformer, there is a change of 15 A in the load current. This results in change of supply current of

A)less than 15 A
B)more than 15 A
C)15 A
D)none of the above

Question 9

No-load speed of which of the following motor will be highest ?

A)Shunt motor
B)Series motor
C)Cumulative compound motor
D)Differentiate compound motor

Question 10

The direction of rotation of a D.C. series motor can be changed by

A)interchanging supply terminals
B)interchanging field terminals
C)either of (a) and (b) above
D)None of the above

Question 11

Which of the following application requires high starting torque ?

A)Lathe machine
B)Centrifugal pump
C)Locomotive
D)Air blower

Question 12

If a D.C. motor is to be selected for conveyors, which rriotor would be preferred ?

A)Series motor
B)Shunt motor
C)Differentially compound motor
D)Cumulative compound motor

Question 13

Which D.C. motor will be preferred for machine tools ?

A)Series motor
B)Shunt motor
C)Cumulative compound motor
D)Differential compound motor

Question 14

Differentially compound D.C. motors can find applicationsrequiring

A)high starting torque
B)low starting torque
C)variable speed
D)frequent on-off cycles

Question 15

Which D.C. motor is preferred for elevators ?

A)Shunt motor
B)Series motor
C)Differential compound motor
D)Cumulative compound motor

Question 16

If the field of a D.C. shunt motor gets opened while motor is running

A)the speed of motor will be reduced %
B)the armature current will reduce
C)the motor will attain dangerously high speed 1
D)the motor will continue to nuvat constantspeed

Question 17

Starters are used with D.C. motors because

A)these motors have high starting torque
B)these motors are not self-starting
C)back e.m.f. of these motors is zero initially
D)to restrict armature current as there is no back e.m.f. whilestarting

Question 18

In D.C. shunt motors as load is reduced

A)the speed will increase abruptly
B)the speed will increase in proportion to reduction in load
C)the speed will remain almost/constant
D)the speed will reduce

Question 19

A D.C. series motor is that which

A)has its field winding consisting of thick wire and lessturns
B)has a poor torque
C)can be started easily without load
D)has almost constant speed

Question 20

For starting a D.C. motor a starter is required because

A)it limits the speed of the motor
B)it limits the starting current to a safe value
C)it starts the motor
D)none of the above

Question 21

The type of D.C. motor used for shears and punches is

A)shunt motor
B)series motor
C)differential compoutid D.C. motor
D)cumulative compound D.C. motor

Question 22

If a D.C. motor is connected across the A.C. supply it will

A)run at normal speed
B)not run
C)run at lower speed
D)burn due to heat produced in the field winding by .eddy currents

Question 23

To get the speed of D.C, motor below the normal without wastage of electrical energy is used.

A)Ward Leonard control
B)rheostatic control
C)All of the above method
D)none of the above method

Question 24

When two D.C. series motors are connected in parallel, the resultant speed is

A)more than the normal speed
B)loss than the normal speed
C)normal speed
D)zero

Question 25

The speed of a D.C. shunt motor more than its full-load speed can be obtained by

A)decreasing the field current
B)increasing the field current
C)decreasing the armature current
D)increasing the armature current