791. Hopkinson’s test on D.C. machines is conducted at_______________?
A. no-load
B. part load
C. full-load
D. overload
792. 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
793. 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
794. Which method of braking is generally used in elevators ?
A. Plugging
B. Regenerative braking
C. Rheostatic braking
D. None of the above
795. In variable speed motor___________?
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
796. When the armature of a D.C. motor rotates, e.m.f. induced is___________?
A. self-induced e.m.f.
B. mutually induced e.m.f.
C. back e.m.f
D. none of the above
797. Where D.C. motor of H.P. 12 or more requires frequent starting, stopping, reversing and speed control______________?
A. drum type controller is used
B. three point starter is used
C. four point starter is used
D. all above can be used
798. If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens____________?
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
799. 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________________?
A. series motor
B. shunt motor
C. compound motor
D. any of the above
800. 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______________?
A. series motor
B. shunt motor
C. compound motor
D. any of the above
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