Which of the following loss in a D.C. generator varies significantly with the load current ?
(A) Field copper loss
(B) Windage loss
(C) Armature copper loss
(D) None of the above
The losses occurring in a D.C. generator are given below. Which loss is likely to have highest proportion at rated load of the generator ?
(A) hysteresis loss
(B) field copper loss
(C) armature copper loss
(D) eddy current loss
In a D.C. generator all of the following could be the effects of iron losses except___________?
(A) Loss of efficiency
(B) Excessive heating of core
(C) Increase in terminal voltage
(D) Rise in temperature of ventilating air
The hysteresis loss in a D.C. machine least depends on____________?
(A) Frequency of magnetic reversals
(B) Maximum value of flux density
(C) Volume and grade of iron
(D) Rate of flow of ventilating air
Regenerative method of braking is based on that___________?
(A) back e.m.f. is less than the applied voltage
(B) back e.m.f. is equal to the applied voltage
(C) back e.m.f. of rotor is more than the applied voltage
(D) none of the above
The main disadvantage of the Ward-Leonard control method is______________?
(A) high initial cost
(B) high maintenance cost
(C) low efficiency at Hght loads
(D) all of the above
In Ward-Leonard control the lower limit of speed is imposed by________?
(A) residual magnetism of the generator
(B) core losses of motor
(C) mechanical losses of motor and generator together
(D) all of the above
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