Thursday, September 10, 2020

Chapter 6 : DC Machines-Page 4

Chapter 6 : DC Machines

31. The pole shoes of dc machines are fastened to the pole core by
A. welding
B. soldering
C. countersunk screws
D. steel clamps

... Answer is (C)



32. ln DC generators, interpole connected field coils are

A. in series with load
B. in parallel with load
C. in series with armature winding
D. in parallel with armature winding

... Answer is (C)


33. Function of compansating vvindings placed in slots in the pole shoes is

A. to avoid flash over around the commutator
B. t
o neutralize cross-magnetising effect
C. to neutralize the demagnetising effect
D. both (b) and (c) above

... Answer is (A)



34. In a dc machine without interpoles, to get improved commutation, the brush shift angle must be

A. varied with change in load
B. kept constant
C. zero degree
D. none of the above

  ... Answer is (A)


35. A dc mache is provided with both in interpole winding (IPW) and compensating winding (CPM). With respect to the armature in parallel
Answer is (D)


36. Interpole are connected in series with the
A.  shunt field winding
B. line
C. armature winding
D. line and armature winding

  ... Answer is (D)



37. Polarity of  DC generator can be reversed by
A. increasing field current
B. reversing field current
C. reversing the direction of rotation
D. reversing field current and also the direction of rotation

  ... Answer is (A)


38. The yoke of a DC machine is

A. is always made o f nonmagnetic material
D. made of magnetic material only for high rpm machines

always made of magnetic material
D. sometimes made of magnetic material

... Answer is (D)


39. The commutator pitch of lap winding is

A. +1
B. -1
C. +1 or -1
D. none of these
  ... Answer is (B)


40. A DC generator has 6 poles. A physical shift brush shift of 6° means an electrical brush shift of
A. 6
B. 18
C. 30
D. 2

  ... Answer is (C)



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