Practice Test: Question Set - 01
1. In D.C. generators, the cause of rapid brush wear may be
- (A) Severe sparking
- (B) Rough commutator surface
- (C) Imperfect contact
- (D) Any of the above
2. The insulating material used between the commutator segments is normally
- (A) Graphite
- (B) Paper
- (C) Mica
- (D) Insulating varnish
3. Eddy currents are induced in the pole shoes of a D.C. machine due to
- (A) Oscillating magnetic field
- (B) Pulsating magnetic flux
- (C) Relative rotation between field and armature
- (D) All above
4. Which of the following statement about D.C. generators is false?
- (A) Compensating winding in a D.C. machine helps
in commutation
- (B) In a D. C. generator interpoles winding is
connected in series with the armature winding
- (C) Back pitch and front pitch are both odd and
approximately equal to the pole pitch
- (D) Equalizing bus bars are used with parallel running
of D.C. shunt generators
5. In a D.C. generator the ripples in the direct e.m.f. generated are reduced by
- (A) Using conductor of annealed copper
- (B) Using commutator with large number of segments
- (C) Using carbon brushes of superior quality
- (D) Using equalizer rings
6. Satisfactory commutation of D.C. machines requires
- (A) Brushes should be of proper grade and size
- (B) Brushes should smoothly run in the holders
- (C) Smooth, concentric commutator properly
undercut
- (D) All of the above
7. In a D.C. generator the number of mechanical degrees and electrical degrees will be the same when
- (A) r.p.m. is more than 300
- (B) r.p.m. is less than 300
- (C) Number of poles is 4
- (D) Number of poles is 2
8. In D.C. generators on no-load, the air gap flux distribution in space is
- (A) Sinusoidal
- (B) Triangular
- (C) Pulsating
- (D) Flat topped
9. Flashing the field of D.C. generator means
- (A) Neutralizing residual magnetism
- (B) Creating residual magnetism by a D.C. source
- (C) Making the magnetic losses of forces parallel
- (D) Increasing flux density by adding extra turns of
windings on poles
10. The following constitute short-circuit in the armature winding.
- (A) Insulation failure between two commutator bars
- (B) Insulation failure between two turns of a coil
- (C) Two of more turns of the same coil getting
grounded
- (D) All of the above
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