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D.C. Generators

Study 120 Electrical Engineering MCQs with correct answers and explanations.

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11Electrical EngineeringMedium

Following energized winding of a D.C. machine should not be opened as it would produce high inductive voltage which may be dangerous to personnel and may cause its own insulation failure.

AInter pole field

BSeries field

CShunt field

DCompensating field

Correct answer

C. Shunt field

Explanation

The correct answer is Shunt field.

12Electrical EngineeringMedium

The e.m.f. generated in a D.C. generator is directly proportional to________?

Anumber of poles

Ball of the above

Cflux/pole

Dspeed of armature

Correct answer

D. speed of armature

Explanation

The correct answer is speed of armature.

13Electrical EngineeringMedium

Magnetic field in a D.C. generator is produced by________?

Apermanent magnets

Belectromagnets

Cnone of the above

Dboth A. and B.

Correct answer

B. electromagnets

Explanation

The correct answer is electromagnets.

14Electrical EngineeringMedium

If a D.C. generator fails to build up the probable cause could not be________?

Afield resistance less than the critical resistance

Bimperfect brush contact

Cfaulty shunt connections tending to reduce the residual magnetism

Dno residual magnetism in the generator

Correct answer

A. field resistance less than the critical resistance

Explanation

The correct answer is field resistance less than the critical resistance.

15Electrical EngineeringMedium

In D.C. generators the polarity of the interpoles________?

Ais the same as that of the immediately preceding pole

Bis the same as that of the main pole ahead

Cis opposite to that of the main pole ahead

Dis neutral as these poles do not play part in generating e.m.f.

Correct answer

B. is the same as that of the main pole ahead

Explanation

The correct answer is is the same as that of the main pole ahead.

16Electrical EngineeringMedium

Satisfactory commutation of D.C. machines requires________?

Aall of the above

Bbrushes should smoothly run in the holders

Cbrushes should be of proper grade and size

Dsmooth, concentric commutator properly undercut

Correct answer

A. all of the above

Explanation

The correct answer is all of the above.

17Electrical EngineeringMedium

In over compounded generator, full load terminal voltage is________?

Aless than no load terminal voltage

Bmore than no load terminal voltage

Cequal to no-load terminal voltage

Dalmost zero

Correct answer

B. more than no load terminal voltage

Explanation

The correct answer is more than no load terminal voltage.

18Electrical EngineeringMedium

The e.m.f. induced in the armature of a shunt generator is 600 V. The armature resistance is 0.1 ohm. If the armature current is 200 A, the terminal voltage will be________?

A600 V

B580 V

C620 V

D640 V

Correct answer

B. 580 V

Explanation

The correct answer is 580 V.

19Electrical EngineeringMedium

As a result of armature reaction, the reduction in the total mutual air gap flux in a D.C. generator is approximately________?

A5 percent

B10 percent

C40 percent

D25 percent

Correct answer

A. 5 percent

Explanation

The correct answer is 5 percent.

20Electrical EngineeringMedium

To avoid formation of grooves in the commutator of a D.C. machine?

Athe brushes of same polarity should track each other

Bbrush position has no effect on the commutator grooving

CNone

Dthe brushes of opposite polarity should track each other

Correct answer

D. the brushes of opposite polarity should track each other

Explanation

The correct answer is the brushes of opposite polarity should track each other.

If a D.C. generator fails to build up the probable cause could not be________?

Afield resistance less than the critical resistance

Bimperfect brush contact

Cfaulty shunt connections tending to reduce the residual magnetism

Dno residual magnetism in the generator

Correct answer

A. field resistance less than the critical resistance

Explanation

The correct answer is field resistance less than the critical resistance.

In D.C. generators the polarity of the interpoles________?

Ais the same as that of the immediately preceding pole

Bis the same as that of the main pole ahead

Cis opposite to that of the main pole ahead

Dis neutral as these poles do not play part in generating e.m.f.

Correct answer

B. is the same as that of the main pole ahead

Explanation

The correct answer is is the same as that of the main pole ahead.

To avoid formation of grooves in the commutator of a D.C. machine?

Athe brushes of same polarity should track each other

Bbrush position has no effect on the commutator grooving

CNone

Dthe brushes of opposite polarity should track each other

Correct answer

D. the brushes of opposite polarity should track each other

Explanation

The correct answer is the brushes of opposite polarity should track each other.