Electrical Machine - DC Motor Objectives: Part 7

[1] The basic requirement of a dc armature winding is that it must be
(a) A closed one
(b) A lap winding
(c) A wave winding
(d) Either b or c
(e) None of the above

Ans: A

[2] The sole purpose of a commutator in a dc generator is to
(a) Increase output voltage
(b) Reduce sparking at brushes
(c) Provide smoother output
(d) Convert the induced ac into dc
(e) None of the above

Ans: D

[3] In small DC machines, armature slots are sometimes not made axial but are skewed, results in
(a) Quieter operation
(b) Slight decrease in losses
(c) Saving of copper
(d) Both a and b
(e) None of the above

Ans:D

[4] The critical resistance of the dc generator is the resistance of
(a) Armature
(b) Field
(c) Load
(d) Brushes
(e) None of the above

Ans: B

[5] In a dc generator, the generator, the generated emf is directly proportional to the
(a) Field current
(b) Pole flux
(c) Number of armature parallel paths
(d) Number of dummy coils
(e) None of the above

Ans: B

[6] The commutation process in a dc generator basically involves
(a) Passage of current from moving armature to a stationary load
(b) Reversal of current in an armature coil as it crosses MNA
(c) Conversion of ac to dc
(d) Suppression of reactance voltage
(e) None of the above

Ans: B

[7] The essential condition for stable parallel operation of two dc generators having similar characteristics is that they should have
(a) Same kilowatt output ratings
(b) Dropping voltage characteristics
(c) Same percentage regulation
(d) Same no load and full load speed
(e) None of the above

Ans: B

[8] An ideal dc generator has .......... voltage regulation.
(a) Low
(b) Zero
(c) Positive
(d) Negative
(e) None of the above

Ans: B

[9] Which generator has poorest voltage regulation
(a) Series
(b) Shunt
(c) Compound
(d) High
(e) None of the above

Ans:A

[10] The voltage regulation of an over compound dc generator is always
(a) Positive
(b) Negative
(c) Zero
(d) High

Ans: B

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