Category: D.C. Generators
In a D.C. generator the critical resistance refers to the resistance of_____________?
A. brushes
B. field
C. armature
D. load
To achieve sparkless commutation brushes of a D.C. generator are rockedm ahead so as to bring them?
A. just ahead of magnetic neutral axis
B. in magnetic neutral axis
C. just behind the magnetic neutral axis
D. none
In a commutator_____________?
A. copper is harder than mica
B. mica and copper are equally hard
C. mica is harder than copper
D. none of the above
In any rotating machine that part which houses the conductors and in which e.m.f. induced is to be utilized is called____________?
A. rotor
B. stator
C. field
D. armature
Compensating windings are used in D.C. generators______________?
A. mainly to reduce the eddy currents by providing local short-circuits
B. to provide path for the circulation of cooling air
C. to neutralise the cross-magnetising effect of the armature reaction
D. none of the above
The series field of a short-shunt D.C. generator is excited by_______________?
A. external current
B. armature current
C. shunt current
D. load current
The main factor which leads to unstable parallel operation of flat and over compounded generators is_____________?
A. their rising voltage characteristics
B. unequal number of turns in their series field windings
C. unequal speed regulation of their primemovers
D. unequal series field resistances
Two D.C. shunt generators, each with armature resistance of 0.02 ohm and field resistance of 50 ohm run in parallel and supply a total current of 1000 amperes to the load circuit. If their e.m.fs. are 270 V and 265 V, their bus bar voltage will be_____________________?
A. 270 V
B. 267.5 V
C. 265 V
D. 257.4 V
When two D.C. series generators are running in parallel, an equilizer bar is used________________?
A. to increase the speed and hence generated e.m.f.
B. to increase the series flux
C. so that two similar machines will pass approximately equal currents to the load
D. to reduce the combined effect of ar-mature reaction of both machines
With a D.C. generator which of the following regulation is preferred ?
A. 100% regulation
B. infinite regulation
C. 50% regulation
D. 1% regulation
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