Question 1

In variable speed motor

Accepted Answer

A)  a stronger commutating field is needed at low speed than at high speed
B)  a weaker commutating field is needed at low speed than at high speed
C)  same commutating field is needed at low speed than at high speed
D)  none of the above is correct B

Question 2

The speed of a D.C. shunt motor is required to be more than full load speed. This is possible by

Accepted Answer

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

Question 3

During rheostat braking of D.C. series motors

Accepted Answer

A)  motor is run as a generator
B)  motor is reversed in direction
C)  motor is run at reduced speed
D)  none A

Question 4

In the D.C. motor the iron losses occur in

Accepted Answer

A)  the field
B)  the armature
C)  the brushes
D)  the commutator

Question 5

The purpose of retardation test on D.C. shunt machines is to find out

Accepted Answer

A)  stray losses
B)  eddy current losses
C)  field copper losses
D)  windage losses

Question 6

Which method of braking is generally used in elevators ?

Accepted Answer

A)  Plugging
B)  Regenerative braking
C)  Rheostatic braking
D)  None of the above

Question 7

D.C. motor is to drive a load which has certain minimum value for most of the time and some peak value for short duration. We will select the

Accepted Answer

A)  series motor
B)  shunt motor
C)  compound motor
D)  any of the above

Question 8

In a D.C. generator, the iron losses mainly take place in

Accepted Answer

A)  yoke
B)  commutator
C)  armature conductors
D)  armature rotor

Question 9

The condition for maximum efficiency for a D.C. generator is

Accepted Answer

A)  eddy current losses = stray losses
B)  hysteresis losses = eddy current losses
C)  copper losses = 0
D)  variable losses = constant losses

Question 10

D.C. generators are normally designed for maximum efficiency around

Accepted Answer

A)  full-load
B)  rated r.p.m.
C)  rated voltage
D)  all of the above

Question 11

Hopkinson's test on D.C. machines is conducted at

Accepted Answer

A)  no-load
B)  part load
C)  full-load
D)  overload

Question 12

One D.C. motor drives another D.C. motor. The second D.C. motor when excited and driven

Accepted Answer

A)  runs as a generator
B)  does not run as a generator
C)  also runs as a motor comes to stop after sometime
D)  none

Question 13

Where D.C. motor of H.P. 12 or more requires frequent starting, stopping, reversing and speed control

Accepted Answer

A)  drum type controller is used
B)  three point starter is used
C)  four point starter is used
D)  all above can be used

Question 14

Which of the following tests will be suitable for testing two similar D.C. series motors of large capacity ?

Accepted Answer

A)  Swinburne's test
B)  Hopkinson's test
C)  Field test
D)  Brake test

Question 15

If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens

Accepted Answer

A)  this will make armature to take heavy current, possibly burning it
B)  this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
C)  nothing will happen to motor
D)  motor will come to stop

Question 16

D.C. generators are installed near the load centres to reduce

Accepted Answer

A)  iron losses
B)  line losses
C)  sparking
D)  corona losses

Question 17

When the armature of a D.C. motor rotates, e.m.f. induced is

Accepted Answer

A)  self-induced e.m.f.
B)  mutually induced e.m.f.
C)  back e.m.f.
D)  none of the above

Question 18

For which types of D.C. motor, dynamic braking is generally used ?

Accepted Answer

A)  Shunt motors
B)  Series motors
C)  Compound motors
D)  All of the above

Question 19

D.C. motor is to a drive a load which is almost nil for certain part of the load cycle and peak value for short duration. We will select this

Accepted Answer