External characteristic = magnetization characteristic ohmic drop armature reaction

External resistance = internal characteristic armature reaction

Internal characteristic = magnetization characteristic ohmic drop

Magnetization characteristic = external characteristic

Practice D.C. Generators Multiple Choice Questions Quiz-4

Q.1

To avoid formation of grooves in the commutator of a D.C. machine

The brushes of opposite polarity should track each other
The brushes of same polarity should track each other
Brush position has no effect on the commutator grooving
All of the above

Q.2

The critical resistance of the D.C. generator is the resistance of

Field
Brushes
Armature
Load

Q.3

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

Lie under South Pole
Lie under North Pole
Lie under interpolar region
Are farthest from the poles

Q.4

A D.C. generator works on the principle of

Lenz's law
Ohm's law
Faraday's law of electromagnetic induction
None of the above

Q.5

In a D.C. generator the critical resistance refers to the resistance of

Brushes
Field
Armature
Load

Q.6

Number of tapings for each equalizer ring is equal to

Number of pole pairs
Number of poles
Number of parallel paths
Number of commutator segments

Q.7

In D.C. generators the polarity of the interpoles

Is the same as that of the main pole ahead
Is the same as that of the immediately preceding pole
Is opposite to that of the main pole ahead
Is neutral as these poles do not play part in generating e.m.f.

Q.8

Inter-pole flux should be sufficient to

Neutralize the commutating self induced e.m.f.
Neutralize the armature reaction flux
Neutralize both the armature reaction flux as well as commutating e.m.f. induced in the coil
Perform none of the above functions

Q.9

A sinusoidal voltage of 5 Hz is applied to the field of a shunt generator. The armature voltage wave

will be zero
will be of 5 Hz
will be of 5 xiVHz
will be of v Hz 5

Q.10

The essential condition for parallel operation of two D.C. generators is that they have

Same kW rating
The same operation r.p.m.
The same drooping voltage characteristics
Same percentage regulation

Q.11

Lap winding is composed of

Any even number of conductors
Any odd number of conductors
That even number which is exact multiple of poles + 2
That even number which is exact multiple of poles

Q.12

Wave winding is composed of

Any even number of conductors
Any odd number of conductors
That even number which is exact multiple of poles + 2
That even number which is exact multiple of poles

Q.13

If a self excited D.C. generator after being installed, fails to build up on its first trial run, the first thing to do is to

reverse the field connections
increase the field resistance
increase the speed of primemover
check armature insulation resistance

Q.14

The armature core of a D.C. generator is usually made of

Silicon steel
Copper
Nonferrous material
Cast-iron

Q.15

The main factor which leads to unstable parallel operation of flat and over compounded generators is

their rising voltage characteristics
unequal number of turns in their series field windings
unequal speed regulation of their primemovers
unequal series field resistances

Q.16

The terminal voltage of a D.C. shunt generator drops on load because of all of the following reasons except

Armature reaction
Armature resistance drop
Field weakening due to armature reaction and armature
Commutation

Q.17

In a D.C. generator the magnetic neutral axis coincides with the geometrical neutral axis, when

There is no load on the generator
The generator runs on full load
The generator runs on overload
The generator runs on designed speed

Q.18

With a D.C. generator which of the following regulation is preferred?

100% regulation
Infinite regulation
50% regulation
1% regulation

Q.19

The number of armature parallel paths in a two-pole D.C. generator having duplex lap winding is

Q.20

Which of the following components of a D.C, generator plays vital role for providing direct current of a D.C. generator?

Dummy coils
Commutator
Eye bolt
Equalizer rings

Q.21

Open circuited armature coil of a D.C. machine is

Identified by the scarring of the commutator segment to which open circuited coil is connected
Indicated by a spark completely around the commutator
Both (A) and (B)
None of the above

Q.22

In a D.C. generator

External resistance = internal characteristic armature reaction
Internal characteristic = magnetization characteristic ohmic drop
External characteristic = magnetization characteristic ohmic drop armature reaction
Magnetization characteristic = external characteristic

Q.23

The terminal voltage of a series generator is 150 V when the load current is 5 A. If the load current is increased to 10 A, the terminal voltage will be

150 V
Less than 150 V
Greater than 150 V
None of the above

Q.24

Which of the following could be lamina proximately the thickness of laminations of a D.C. machine?

0.005 mm
0.05 mm
0.5 m
5 m

Q.25

The commutator segments are connected to the armature conductors by means of

Copper lugs
Resistance wires
Insulation pads
Brazing

Q.26

In a D.C. generator the ripples in the direct e.m.f. generated are reduced by

Using conductor of annealed copper
Using commutator with large number of segments
Using carbon brushes of superior quality
Using equalizer rings

Q.27

Magnetic field in a D.C. generator is produced by

Electromagnets
Permanent magnets
Both (A) and (B)
None of the above

Q.28

For a D.C. machines laboratory following type of D.C. supply will be suitable

Mercury are rectifier
Rotary converter
Induction motor D.C. generator set
Synchronous motor D.C. generator set

Q.29

A separately excited generator as compared to a self-excited generator

Is amenable to better voltage control
Is more stable
Has exciting current independent of load current
Has all above features

Q.30

In lap winding, the number of brushes is always

Double the number of poles
Same as the number of poles
Half the number of poles
Two