ELECTRICAL MACHINES QUIZ

A dc shunt motor has external resistance Ra and Rf in the armature and field circuits respectively. Armature current at starting can be reduced by keeping

Rf maximum and Ra minimum

Ra minimum and Rf minimum

Ra maximum and Rf maximum

Ra maximum and Rf minimum

TRUE ANSWER : ?
YOUR ANSWER : ?

Which of the following represents the operating region of slip in a 1-phase induction motor?

0 < S < 1

-2 < S < 2

-1 < S < 1

0 < S < 2

TRUE ANSWER : ?
YOUR ANSWER : ?

A self-excited shunt generator fails to build up, because 1. the field circuit is open 2. The armature circuit is open 3. the residual magnetism is absent 4. The direction of rotation is wrong From these, the correct answer is

1, 3

3 only

1, 2, 3 and 4

1, 2 and 3

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YOUR ANSWER : ?

For same HP rating and full load speed which of following motor has poor starting torque?

Cummulative compound.

Differently compounded.

Shunt.

Series.

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YOUR ANSWER : ?

If the load current and flux of a DC motor are held constant and voltage applied across it armature is increased by 5%, the speed of the motor will

Remain unchanged.

Depends on other factor.

Reduce by 5%.

Increase by 5%.

TRUE ANSWER : ?
YOUR ANSWER : ?

In a DC series generator, the terminal voltage with increase in load will

decrease

remain nearly constant

increase gradually and then stay at rated voltage

increase to rated voltage and then may decrease

TRUE ANSWER : ?
YOUR ANSWER : ?

In V/f speed control of 3-phase induction motor, with increase in frequency, the slip at which maximum torque occurs

None of these

increase.

either of these.

decrease.

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YOUR ANSWER : ?

Consider the following statements : 1. interpole windings are connected in series with armature windings 2. polarity of interpoles must be the same as that of the main poles in advance 3. distortion of the main field under the pole shoes is not affected by the use of interpoles From above, the correct answer is

2 and 3

1 and 3

1 alone

1 and 2

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YOUR ANSWER : ?

In a synchronous motor, damper windings are provided on

pole faces.

None of these

rotor shaft.

stator frame.

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YOUR ANSWER : ?

In a DC shunt generator working on load, the brushes are moved forward in the direction of rotation, as a result of this, commutation will

worsen and terminal voltage will fall

worsen and terminal voltage will rise.

improve and terminal voltage will rise .

improve but terminal voltage will fall.

TRUE ANSWER : ?
YOUR ANSWER : ?

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