Thursday, September 10, 2020

Chapter 6 : DC Machines-Page 3

Chapter 6 : DC Machines

21. V xB=E is the equation of the electrical machines which

A. works as a motor
B. converts mechanical energy into electrical energy
C. is a dc machines
D. has magnetic poles


... Answer is (B)

 

 
 

22. Each commutator segment is connected to the armature conductor by means of

A. Resistance wire
B. Carbon brush
C. Insulator
D. Copper lug

... Answer is (D)

 
 
 

23. In a dc generator, sparking between brushes and commutator surface may be due to

A. to rapid reversal of current
B. 
Under-commutation
C.
Over-commutation
D. Any of the above

... Answer is (D)

 

 
 

24. Brushes for commutators for 220 V dc generator are generally made of

A. electrographite
B. graphited copper

C.
Copper
D. Carbon Copper

  ... Answer is (A)

 

 
 
25. Commutator of a dc machine acts as a
A. fullwave rectifier
B. halfwave rectifier
C. inverter
D. controlled rectifier
 
  ...
Answer is (A)

 
 
 

26. The maximum nuber of brushes which machine may be used in an electrical machine isnumber of poles i the machine equal to

A. 4
B. 2
C. 1
D. either (b) or (c)

  ... Answer is (D)

 

 
 

27. Equalizer rings can be used by only

A. lap wound  armatures only
B. wave wound armatures only
C. both lap and wave wound armatures
D. none of these

... Answer is (A)

 
 

28. Width of a dc generator insulation equals the width of

A. one commutator segment and one mica segment
B. one commutator mica insulation
C. two commutator segments and two mica insulations
D. two commutator segments and one mica insulations

... Answer is (A)

 
 

29. The rotating part is known as

A. Pole
B. Stator
C. Armature
D. Commutator
 
  ... Answer is (C)

 
 

30. The yoke in a small dc machine is made of


A.
mild steel
B. grain oriented steel

C.
cast iron
D. cast steel

  ... Answer is (C)

 

 

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