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.Management Sciences
Category: Electrical Machine Design
The action of electromagnetic machines can be related to which of the following basic principles __________?
A. Induction
B. Interaction
C. Alignment
D. All of the above
Which of the following methods does not take into account the maximum temperature rise under variable load conditions ?
A. Equivalent power method
B. Equivalent current method
C. Method of average losses
D. Equivalent torque method
A current density of __________ is ilsed for large power transformers with forced circulation of oil or with water cooling coils?
A. 1.5 to 2.5 A/mm2
B. 3.5 to 4.5 A/mm2
C. 4.0 to 5.0 A/mm2
D. 5.4 to 6.2 A/mm2
On which of the following variables heat convected depends ?
A. Power density
B. Temperature difference between heated surface and coolant
C. Thermal resistivity, density, specific heat
D. Gravitational constant
E. All of the above
In induction motors, the length of air gap in kept as small as mechanically possible is order to have____________?
A. low power factor
B. high power factor
C. high over load capacity
D. any of the above
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____________?
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
Aluminium when adopted as a conductor material in __________ transformers, decreases the overall cost of the transformer?
A. small size
B. medium size
C. large size
D. any of the above size
The resistivity of water should not be less than_____________?
A. 10 Q m
B. 100 Q m
C. 1000 Q m
D. 2000 Q m
In D.C. machines the number of slots per pole usually lies___________?
A. between 2 to 4
B. between 6 to 8
C. between 9 to 16
D. between 20 to 30
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