is usually used for brush rockers____________?
A. Mild steel
B. Copper
C. Aluminium
D. Cast-iron
Electrical Machine Design
Which of the following brushes can be used for high values of current density ?
Which of the following brushes can be used for high values of current density ?
A. Metal graphite brushes
B. Hard carbon brushes
C. Electro-graphitic brushes
D. Natural graphite brushes
Which of the following problem arises in D.C. motors which are fed from thyristor bridge circuits ?
Which of the following problem arises in D.C. motors which are fed from thyristor bridge circuits ?
A. Increased I R losses
B. Increased core losses
C. Poor commutation
D. Change in motor parameters
E. All of the above
In a D.C. machine the number of brush arms is _________ the number of poles?
In a D.C. machine the number of brush arms is _________ the number of poles?
A. less than
B. equal to
C. greater than
D. none of the above
D.C. machines designed with a large value of air gap length have_____________?
D.C. machines designed with a large value of air gap length have_____________?
A. worst, ventilation
B. poor ventilation
C. better ventilation
D. none of the above
In D.C. machines the usual limit of slot pitch is________________?
In D.C. machines the usual limit of slot pitch is________________?
A. between 5 to 10 mm
B. between 10 to 15 mm
C. between 15 to 20 mm
D. between 25 to 35 mm
The operation of a D.C. machine with large air gap lengths is comparatively_____________?
The operation of a D.C. machine with large air gap lengths is comparatively_____________?
A. quiet
B. noisy
C. either of the above
D. none of the above
In D.C. machines, ir order to prevent excessive distortion of field form by the armature reaction, the field mmf must be made____________?
In D.C. machines, ir order to prevent excessive distortion of field form by the armature reaction, the field mmf must be made____________?
A. equal to that of armature mmf
B. less in comparison with the armature mmf
C. large in comparison with the armature mmf
D. none of the above
In a D.C. machine, the value of peripheral speed should not, normally, exceed___________?
In a D.C. machine, the value of peripheral speed should not, normally, exceed___________?
A. 10 m/s
B. 20 m/s
C. 30 m/s
D. 40 m/s
The weight of copper of both armature and field windings decreases with __________ in number of poles?
The weight of copper of both armature and field windings decreases with __________ in number of poles?
A. increase
B. decrease
C. either of the above
D. none of the above