Dc Generator Multiple choice questions and answers

1. The armature of D.C. generator is laminated to

(a) reduce the bulk

(b) provide the bulk

(c) insulate the core

(d) reduce eddy current loss

2. The field coils of D.C. generator are usually made of

(a) mica

(b) copper

(c) cast iron

(d) carbon

3. The bearings used to support the rotor shafts are generally

(a) ball bearings

(b) bush bearings

(c) magnetic bearmgs

(d) needle bearings

4. In lap winding, the number of brushes is always

(a) double the number of poles

(b) same as the number of poles

(c) half the number of poles

(d) two

5. Iron losses in a D.C. machine are independent of variations in

1 point

(a) speed

(b) load

(c) voltage

(d) speed and voltage

6. Brushes of D.C. machines are made of

1 point

(a) carbon

(b) soft copper

(c) hard copper

(d) all of above

7. In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be

1 point

(a) 4

(b) 8

(c) 16

(d) 32

8. The insulating material used between the commutator segments is normally

1 point

(a) graphite

(b) paper

(c) mica

(d) insulating varnish

9. Equilizer rings are required in case armature is

1 point

(a) wave wound

(b) lap wound

(c) delta wound

(d) duplex wound

10. Welding generator will have

1 point

(a) lap winding

(b) wave winding

(c) delta winding

(d) duplex wave winding

11. Magnetic field in a D.C. generator is produced by

1 point

(a) electromagnets

(b) permanent magnets

(c) both (a) and (b)

12. In D.C. generators, lap winding is used for

1 point

(a) high voltage, high current

(b) low voltage, high current

(c) high voltage, low current

(d) low voltage, low current

13. The purpose of providing dummy coils in a generator is

1 point

(a) to reduce eddy current losses

(b) to enhance flux density

(c) to amplify voltage

(d) to provide mechanical balance for the rotor

14. In a D.C. generator the critical resistance refers to the resistance of

1 point

(a) brushes

(b) field

(c) armature

(d) load

15. In a D.C. machine stray loss is the sum of

1 point

(a) total copper loss and mechanical loss

(b) armature copper loss and iron loss

(c) shunt field copper loss and mechanical loss

(d) iron loss and mechanical loss

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