DC GENERATOR PART - 2

1. In D.C. generators, current to the external circuit from armature is given through
(a) commutator
(b) solid connection
(c) slip rings
(d) none of above

Ans: a

2. Brushes of D.C. machines are made of
(a) carbon
(b) soft copper
(c) hard copper
(d) all of above

Ans: a

3. If B is the flux density, I the length of conductor and v the velocity of conductor, then induced e.m.f. is given by
(a)Blv (b)Blv2 (c)Bl2v (d)Bl2v2

Ans: a

4. In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be
(a) 4
(b) 8
(c) 16
(d) 32

Ans: b

5. The material for commutator brushes is generally
(a) mica
(b) copper
(c) cast iron
(d) carbon

Ans: d

6. The insulating material used between the commutator segments is normally
(a) graphite
(b) paper
(c) mica
(d) insulating varnish

Ans: c

7. In D.C. generators, the brushes on commutator remain in contact with conductors which
(a) lie under south pole
(b) lie under north pole
(c) lie under interpolar region
(d) are farthest from the poles

Ans: c

8. If brushes of a D.C. generator are moved in order to bring these brushes in magneticneutral axis, there will be
(a) demagnetisation only
(b) cross magnetisation as well as magnetisation
(c) crossmagnetisation as well as demagnetising
(d) cross magnetisation only

Ans: c

9. Armature reaction of an unsaturated D.C. machine is
(a) crossmagnetising
(b) demagnetising
(c) magnetising
(d) none of above

Ans: a

10. D.C. generators are connected to the busbars or disconnected from them only under the floating condition
(a) to avoid sudden loading of the primemover
(b) to avoid mechanicaljerk to the shaft
(c) to avoid burning of switch contacts
(d) all above

Ans: d

11. Eddy currents are induced in the pole shoes of a D.C. machine due to
(a) oscillating magnetic field
(b) pulsating magnetic flux
(c) relative rotation between field and armature
(d) all above

Ans: c

12. In a D.C. machine, short-circuited field coil will result in
(a) odour of barning insulation
(b) unbalanced magnetic pull producing vibrations
(c) reduction of generated voltage for which excitation has to be increased to maintain the voltage
(d) all above

Ans:

13. Equilizer rings are required in case armature is
(a) wave wound
(b) lap wound
(c) delta wound
(d) duplex wound

Ans: b

14. Welding generator will have
(a) lap winding
(b) wave winding
(c) delta winding
(d) duplex wave winding

Ans: a

15. In case of D.C. machine winding, number of commutator segments is equal to
(a) number of armature coils
(b) number of armature coil sides
(c) number of armature conductors
(d) number of armature turns

Ans: a

16. For a D.C. machines laboratory following type of D.C. supply will be suitable
(a) rotary converter
(b) mercury are rectifier
(c) induction motor D.C. generator set
(d) synchronous motor D.C. generator set

Ans: c

. 17. The function of pole shoes in the case of D.Cmachine is
(a) to reduce the reluctance of the magnetic path
(b) to spread out the flux to achieve uniform flux density
(c) to support the field coil
(d) to discharge all the above functions

Ans: d

18. In the case of lap winding resultant pitch is
(a) multiplication of front and back pitches
(b) division of front pitch by back pitch
(c) sum of front and back pitches
(d) difference of front and back pitches

Ans: d

19. A D.C. welding generator has
(a) lap winding
(b) wave moving
(c) duplex winding
(d) any of the above

Ans: a

20. As a result of armature reaction, the reduction in the total mutual air gap flux in a D.C. generator is approximately
(a) 40 percent
(b) 25 percent
(c) 10 percent
(d) 5 percent

Ans: d