D.C. Motors

Which method of braking is generally used in elevators ?

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

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

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

During rheostat braking of D.C. series motors_____________?

A. motor is run as a generator
B. motor is reversed in direction
C. motor is run at reduced speed

Hopkinson’s test on D.C. machines is conducted at_______________?

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

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

A. Swinburne’s test
B. Hopkinson’s test
C. Field test
D. Brake test

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

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

D.C. generators are installed near the load centres to reduce_____________?

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

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

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

D.C. generators are normally designed for maximum efficiency around_____________?

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

The condition for maximum efficiency for a D.C. generator is______________?

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