# DC Machines

31 Questions | Total Attempts: 1056  Settings Create your own Quiz This is a short quiz on DC machines fundamentals

• 1.
Winding used for low voltage high current
• A.

Lap winding

• B.

Wave Winding

• C.

Gram ring winding

• D.

Open winding

• 2.
No. of parallel paths in lap winding=_________
• A.

Number of poles

• B.

2

• C.

4

• D.

6

• 3.
In long shunt compound generator Ise = ____________
• A.

Ia-Ish

• B.

IL

• C.

Ia

• D.

Ia+Ish

• 4.
Generated emf is __________ speed of prime mover
• A.

Directly proportional to

• B.

Inversely proportional to

• C.

Equal to

• D.

Less than

• 5.
For a 4 pole lap wound DC generator with 32 armature slots, average pitch is
• A.

2

• B.

4

• C.

8

• D.

16

• 6.
________ compound generator is used for arc welding
• A.

Long shunt

• B.

Short shunt

• C.

Differential

• D.

Commulative

• 7.
% efficiency = ___________
• A.

(Po/Pi)x100

• B.

(Po/Po+Losses)x100

• C.

Both a & b

• D.

None of above

• 8.
If VN > VL , Voltage regulation is _________
• A.

Negative

• B.

Positive

• C.

Zero

• D.

1

• 9.
Power P (in watts) = __________
• A.

BHPx746

• B.

BHP/746

• C.

BHPx764

• D.

BHP/764

• 10.
Series generators are used for
• A.

Series arc lighting

• B.

Voltage booster

• C.

Regenerative breaking

• D.

All of above

• 11.
A 110V, 1000 rpm generator will generate ____ V at 1100 rpm
• A.

220

• B.

200

• C.

150

• D.

120

• 12.
Cu-Losses are also known as
• A.

I2R

• B.

IR2

• C.

V2/R

• D.

VI

• 13.
_________ field winding has small number of turns of thick copper wire.
• A.

Shunt

• B.

Series

• C.

Compund

• D.

Separately excited

• 14.
Carbon brushes are preferred on copper brushes because of
• A.

Armature reaction

• B.

Reduced reactance voltage

• C.

Hardness of material

• D.

Low resistance

• 15.
In Fleming's right-hand rule, the thumb point towards
• A.

Direction of flux

• B.

Direction of induced e.m.f.

• C.

Direction of motion of conductor

• D.

Any of above

• 16.
The output voltage of a simple d.c. generator is
• A.

A.c. square wave.

• B.

A.c. sinusoidal wave

• C.

Pure d.c

• D.

Pulsating d.c

• 17.
When tow generators are running in parallel and field of one of them is weakened too much then it will
• A.

Deliver large share of the total load

• B.

Deliver small share of the total load

• C.

Run in the opposite direction

• D.

Run as a motor in the same direction

• 18.
In shunt generator interpole winding carries ____ current
• A.

Armature

• B.

Shunt field

• C.

• D.

None of these

• 19.
Due to which of the following reasons a separately excited generator is better
• A.

Low price

• B.

Exciting current is independent of load current

• C.

Low armature resistance

• D.

All of above

• 20.
Why is the armature of a d.c. machine made of silicon steel
• A.

To reduce eddy current loss

• B.

To reduce hysteresis loss

• C.

Ease of creating slots

• D.

To achieve high permeability

• 21.
compound generator is said to be flat compounded if VFL
• A.

> VNL

• B.

< VNL

• C.

= VNL

• D.

= 2VNL

• 22.
The commutator segments of a d.c. machine are made of
• A.

Carbon

• B.

Copper

• C.

Mica

• D.

Ceramic

• 23.
If the number of poles in a lap wound generator be doubled, then the generated e.m.f .will
• A.

Become half

• B.

Become double

• C.

Increase to four times

• D.

Remain constant

• 24.
Which of the following d.c. generator can build up without any residual magnetism
• A.

Compound generator

• B.

Self-excited generator

• C.

Series generator

• D.

Shunt generator

• 25.
The efficiency of a d.c. machine is maxiinum when
• A.

Variable losses = constant losses

• B.

Stray losses are = copper losses

• C.

Field copper losses = armature copper losses

• D.

Magnetic losses - windage loss.

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