Electrical Machine - I (3140913) MCQs

MCQs of DC Machines

Showing 141 to 150 out of 167 Questions
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141.
In DC generators, the brushes remain in contact with conductors which
(a) lie under the north pole
(b) lie under the south pole
(c) lie in the inter polar gaps
(d) there is no hard and fast rule for this
Answer:

Option (c)

142.
In a DC generator, the ripples in the direct emf generated are reduced by
(a) using commutator with a large number of segments
(b) using equalizer rings
(c) using conductor of annealed copper
(d) using carbon brushes of superior quality
Answer:

Option (a)

143.
The voltage drop for which of the following types of a brush can be expected to be least?
(a) Carbon brushes
(b) Metal graphite brushes
(c) Graphite brushes
(d) None of the above
Answer:

Option (b)

144.
Satisfactory commutation of DC machine requires
(a) smooth, concentric commutator properly undercut
(b) brushes should smoothly run in the holders
(c) brushes should be of proper grade and size
(d) all of the above
Answer:

Option (d)

145.
To achieve sparkless commutation brushes of DC generator are rocked ahead so as to bring them
(a) in the magnetic neutral axis
(b) just behind the magnetic neutral axis
(c) just ahead of the magnetic neutral axis
(d) none of the above
Answer:

Option (c)

146.
In a DC generator in order to reduce sparking at brushes, the self-induced emf in the coil is neutralized by all of the following except
(a) dummy coils
(b) inter poles
(c) shifting of the axis of brushes
(d) compensating winding
Answer:

Option (b)

147.
The rapid wear of brushes takes place due to
(a) rough commutator bars
(b) excessive spring pressure
(c) abrasion from dust
(d) all of the above factor
Answer:

Option (d)

148.
In a DC shunt generator working on load, the brushes are moved forward in the direction of rotation, as a result of this, the commutation will
(a) improve and terminal voltage will rise
(b) improve but the terminal voltage will fall
(c) worsen and terminal voltage will rise
(d) worsen and terminal voltage will fall
Answer:

Option (a)

149.
In a DC generator, the actual flux distribution depends upon
(a) the shape of the pole shoe
(b) size of an air gap
(c) clearance between tips of the adjacent pole shoes
(d) all of the above
Answer:

Option (d)

150.
Flashing the field of DC generator means
(a) making the magnetic losses forces parallel
(b) increasing flux density by adding extra turns of the winding
(c) neutralizing residual magnetism
(d) creating residual magnetism by a DC source
Answer:

Option (d)

Showing 141 to 150 out of 167 Questions
12 13 14 15 16 17