thefunword.com – MCQs, Mock Tests | Engineering Engineering Electrical Engineering Dc Motors part3

Which of the following steps is likely to result in reduction of hysteresis loss in a D.C. generator ?

1. Providing laminations in armature core
2. Providing laminations in stator
3. Using non-magnetic material for frame
4. Using material of low hysteresis co-efficient for armature core material

✅ Correct Answer: 4

Which of the following loss in a D.C. generator is dissipated in the form of heat?

1. Mechanical loss
2. Core loss
3. Copper loss
4. All of the above

✅ Correct Answer: 4

In a D.C. generator all of the following could be the effects of iron losses except

1. Loss of efficiency
2. Excessive heating of core
3. Increase in terminal voltage
4. Rise in temperature of ventilating air

✅ Correct Answer: 3

For constant torque drive which speed control method is preferred ?

1. Field control
2. Armature voltage control
3. Shunt armature control
4. Mechanical loading system

✅ Correct Answer: 2

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 ?

1. hysteresis loss
2. field copper loss
3. armature copper loss
4. eddy current loss

✅ Correct Answer: 3

The hysteresis loss in a D.C. machine least depends on

1. Frequency of magnetic reversals
2. Maximum value of flux density
3. Volume and grade of iron
4. Rate of flow of ventilating air

✅ Correct Answer: 4

Which motor should not be started on no-load ?

1. Series motor
2. Shunt motor
3. Cumulatively compounded motor
4. Differentially compounded motor.

✅ Correct Answer: 4

If the terminals of armature of D.C. motor are interchanged this action will offer following kind of braking (o) regenerative

1. plugging
2. dynamic braking
3. none of the above
4. any of the above

✅ Correct Answer: 1

In a manual shunt motor starter

1. over load relay is connected in series and no volt relay in parallel with the load
2. over load relay is connected in paral?lel and no volt relay in series with the load
3. over load relay and no volt relay are both connected in series with the load
4. over load relay and no volt relay are both connected in parallel with the load

✅ Correct Answer: 1

Why are the D.C. motors preferred for traction applications ?

1. Torque and speed are inversely proportional to armature current
2. Torque is proportional to armature current
3. Torque is proportional to square root of armature current
4. The speed is inversely proportional to the torque and the torque is proportional to square of armature current

✅ Correct Answer: 4

The plugging gives the

1. zero torque braking
2. smallest torque braking
3. highest torque braking
4. none of the above

✅ Correct Answer: 3

Which of the following losses are significantly reduced by laminating the core of a D.C. generator ?

1. Hysteresis losses
2. Eddy current losses
3. Copper losses
4. Windage losses

✅ Correct Answer: 2

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

1. series motor
2. shunt motor
3. compound motor
4. any of the above

✅ Correct Answer: 3

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

1. drum type controller is used
2. three point starter is used
3. four point starter is used
4. all above can be used

✅ Correct Answer: 1

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

1. full-load
2. rated r.p.m.
3. rated voltage
4. all of the above

✅ Correct Answer: 1

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

1. stray losses
2. eddy current losses
3. field copper losses
4. windage losses

✅ Correct Answer: 1

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

1. series motor
2. shunt motor
3. compound motor
4. any of the above

✅ Correct Answer: 1

In variable speed motor

1. a stronger commutating field is needed at low speed than at high speed
2. a weaker commutating field is needed at low speed than at high speed
3. same commutating field is needed at low speed than at high speed
4. none of the above is correct

✅ Correct Answer: 2

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

1. the field
2. the armature
3. the brushes
4. the commutator

✅ Correct Answer: 2

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

1. runs as a generator
2. does not run as a generator
3. also runs as a motor comes to stop after sometime
4. also runs as a motor comes to stop after sometime

✅ Correct Answer: 1

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

1. reducing the field current
2. decreasing the armature current
3. increasing the armature current
4. increasing the excitation current

✅ Correct Answer: 1

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

1. this will make armature to take heavy current possibly burning it
2. this will result in excessive speed possibly destroying armature due to excessive
3. centrifugal stresses
4. nothing will happen to motormotor will come to stop

✅ Correct Answer: 1

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

1. no-load
2. part load
3. full-load
4. overload4

✅ Correct Answer: 3

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

1. eddy current losses = stray losses
2. hysteresis losses = eddy current losses
3. copper losses = 0
4. variable losses = constant losses

✅ Correct Answer: 4

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

1. iron losses
2. line losses
3. sparking
4. corona losses

✅ Correct Answer: 2

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

1. self-induced e.m.f.
2. mutually induced e.m.f.
3. back e.m.f.
4. none of the above

✅ Correct Answer: 3

Which method of braking is generally used in elevators ?

1. Plugging
2. Regenerative braking
3. Rheostatic braking
4. None of the above

✅ Correct Answer: 1

Which D.C. motor has got maximum self relieving property ?

1. Series motor
2. Shunt motor
3. Cumulatively compounded motor
4. Differentially compounded motor

✅ Correct Answer: 1

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

1. yoke
2. commutator
3. armature conductors
4. armature rotor

✅ Correct Answer: 4

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Engineering Electrical Engineering Dc Motors part3