# DC Generator

76 Questions | Total Attempts: 487  Settings Create your own Quiz .

• 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.
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

• 9.
In a D.C. machine stray loss is the sum of
• A.

Total copper loss and mechanical loss

• B.

Armature copper loss and iron loss

• C.

Shunt field copper loss and mechanical loss

• D.

Iron loss and mechanical loss

• 10.
Which of the following generator will have negligible terminal voltage while running on no-load?
• A.

Series generator

• B.

Shunt generator

• C.

Compound generator

• D.

Separately excited generator

• 11.
In a separately excited generator supplying rated load the armature reaction:
• A.

Is always present

• B.

Is always absent

• C.

May be sometimes present

• D.

None of the above

• 12.
. When two D.C. series generators are running in parallel, an equalizer 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.

Efect of armature reaction To reduce the combined of both machines

• 13.
A D.C. generator works on the principle of
• A.

Lenz's law

• B.

Ohm's law

• C.

Faraday's law of electromagnetic induction

• D.

None of the above

• 14.
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

• 15.
In a D.C. generator the critical resistance can be increased by
• A.

Increasing its field resistance

• B.

Decreasing its field resistance

• C.

Increasing its speed

• D.

Decreasing its speed

• 16.
For both lap and wave windings, there are as many commutator bars as the number of
• A.

Slots

• B.

Armature conductors

• C.

Winding elements

• D.

Poles

• 17.
In case of D.C. machine winding, number of commutator segments is equal to
• A.

Number of armature coils

• B.

Number of armature coil sides

• C.

Number of armature conductors

• D.

Number of armature turns

• 18.
A  D.C. welding generator has
• A.

Lap winding

• B.

Wave moving

• C.

Duplex winding

• D.

Any of the above

• 19.
DC shunt generator has terminal voltage versus load current characteristic which is
• A.

Constant

• B.

Slightly drooping

• C.

Slightly rising

• D.

Highly drooping

• 20.
The material for commutator brushes is generally
• A.

mica

• B.

Copper

• C.

Cast iron

• D.

carbon

• 21.
The insulating material used between the commutator segments is normally
• A.

graphite

• B.

Paper

• C.

Mica

• D.

insulating varnish

• 22.
3.In D.C. generators, the brushes on commutator remain in contact with conductors which
• A.

lie under south pole

• B.

Lie under north pole

• C.

Lie under interpolar region

• D.

are farthest from the poles

• 23.
4.If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be
• A.

demagnetisation only

• B.

Cross magnetisation as well as mag¬netisation

• C.

Crossmagnetisation as well as demagnetising

• D.

cross magnetisation only

• 24.
Armature reaction of an unsaturated D.C. machine is
• A.

crossmagnetising

• B.

Demagnetising

• C.

Magnetising

• D.

none of above

• 25.
D.C. generators are connected to the busbars or disconnected from them only under the floating condition
• A.

to avoid sudden loading of the primemover

• B.

To avoid mechanicaljerk to the shaft

• C.

To avoid burning of switch contacts

• D.

all above Back to top