In case of D.C. machines mechanical losses are primary function of
speed
none of above
voltage
current
speed
Which of the following motors is usually used in house-hold refrigerators ?
Single phase induction motor (split phase start or induction run motor)
D.C. series motor
D.C. shunt motor
Reluctance motor
Single phase induction motor (split phase start or induction run motor)
Which of the following losses are significantly reduced by laminating the core of a D.C. generator ?
Windage losses
Eddy current losses
Hysteresis losses
Copper losses
Eddy current losses
The main disadvantage of the Ward-Leonard control method is
all of the above
high initial cost
high maintenance cost
low efficiency at Hght loads
all of the above
The hysteresis loss in a D.C. machine least depends on
Volume and grade of iron
Maximum value of flux density
Frequency of magnetic reversals
Rate of flow of ventilating air
Rate of flow of ventilating air
In a D.C. generator all of the following could be the effects of iron losses except
Loss of efficiency
Excessive heating of core
Increase in terminal voltage
Rise in temperature of ventilating air
Increase in terminal voltage
In a manual shunt motor starter
over load relay is connected in series and no volt relay in parallel with the load
over load relay and no volt relay are both connected in parallel with the load
over load relay and no volt relay are both connected in series with the load
over load relay is connected in parallel and no volt relay in series with the load
over load relay is connected in series and no volt relay in parallel with the load
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 ?
armature copper loss
field copper loss
hysteresis loss
eddy current loss
armature copper loss
Which of the following loss in a D.C. generator varies significantly with the load current ?
None of the above
Armature copper loss
Field copper loss
Windage loss
Armature copper loss
D.C. shunt motors are used for driving
machine tools
trains
cranes
hoists
machine tools
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