Next Transformer Practice Quiz Test-1

BASIC NEC 2023

DC Generator theory

Free online DC generator theory practice test. 25 basic electrical questions on generator losses, EMF equation, types of DC generators, armature reaction, commutation, critical field resistance, and generator characteristics. Good for electrician exam prep.

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A DC generator changes mechanical energy into DC electrical energy using the principle of electromagnetic induction. Key ideas to know before you start: the EMF equation E = ΦZNP / 60A links flux, speed, and winding design to output voltage. Generators can be self-excited (shunt, series, compound) or separately excited. Armature reaction is the effect of armature current on the main field, and it shifts the magnetic neutral plane. Losses are grouped as constant losses (iron and mechanical) and variable losses (copper, changing with load current).

25

Questions

38 min

Time

70%

Pass

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DC Generator theory — Question List

Question 1: In a Compound Generator, which of the following losses VARIES with the load current?

Copper losses
Magnetic losses
Mechanical Losses

Question 2: If a DC Generator is Operated at lower speed than rated speed, the DC generator ..............

may be over heated
may be over excited
will damage

Question 3: The voltage of a DC Generator can be controlled by ............

varying the prime mover speed
varying the field current
changing the brush positions

Question 4: Which of the following generator part changes the induced AC voltage to the DC voltage at generator terminals?

Armature
commutator
brushes
rotor

Question 5: In DC Generator, which of the following is the effect of <em>armature reaction</em>?

Motoring effect
high sparking at brushes on commutator
damages the field winding
damages the armature winding

Question 6: Which of the following is not required in DC generator to generate DC Voltage?

magnetic field
conductor
relative motion
slip rings

Question 7: The torque developed in DC Generator is inversely proportional to armature current.

True
False

Question 8: Which of the following DC Generator is used when a constant output voltage is required?

DC Shunt Generator
DC Series Generator

Question 9: In DC Generator, The armature current is inversely proportional to load current.

True
False

Question 10: In DC Series generator, the terminal voltage changes with the change in load current.

True
False

Question 11: The EMF equation of a DC generator is E = ΦZNP / 60A. In this equation, what does the letter "A" represent?

Number of poles
Number of parallel paths in the armature winding
Number of armature conductors
Flux per pole

Question 12: Based on excitation, a DC generator in which the field winding gets its current from a separate DC source is called a:

Shunt generator
Series generator
Separately excited generator
Compound generator

Question 13: Armature reaction in a DC generator is caused by:

The magnetic field produced by the armature current
The speed of the prime mover
The resistance of the field winding
The direction of rotation

Question 14: The process of changing the AC voltage induced in the armature winding into DC voltage at the generator terminals is called:

Excitation
Commutation
Interpolation
Compounding

Question 15: What is the main purpose of interpoles (commutating poles) in a DC generator?

To increase the output voltage
To improve commutation and reduce brush sparking
To reduce the speed of the armature
To increase the number of parallel paths

Question 16: In a DC generator armature, a wave winding is normally chosen over a lap winding when the design needs:

Higher voltage at lower current
Higher current at lower voltage
Lower cost of copper only
No difference from lap winding

Question 17: A self-excited DC shunt generator will fail to build up voltage if the field circuit resistance is:

Lower than the critical field resistance
Higher than the critical field resistance
Equal to the armature resistance
Zero

Question 18: A self-excited DC generator needs which of the following to start building up its own voltage?

Residual magnetism in the pole cores
An external DC supply at all times
A capacitor bank connected to the armature
High speed prime mover only

Question 19: In a CUMULATIVE compound DC generator, the series field flux and the shunt field flux:

Aid (add to) each other
Oppose each other
Have no relation to each other
Cancel each other completely

Question 20: Why is an equalizer connection (equalizer ring) used when two or more compound DC generators operate in parallel?

To keep the load shared correctly and prevent unstable parallel operation
To increase the output voltage of each generator
To reduce the number of brushes needed
To eliminate the need for a commutator

Question 21: Due to armature reaction in a DC generator, the magnetic neutral plane shifts:

In the direction of rotation
Opposite to the direction of rotation
It never shifts
Only at no load

Question 22: A DC generator gives its maximum efficiency at the load point where:

Variable losses equal the constant losses
Variable losses are zero
Constant losses are zero
The generator runs at half rated speed

Question 23: A DC series generator, which gives an output voltage that rises sharply with load current, is mainly suited for use as a:

General lighting supply
Booster on long feeders
Battery charging at constant voltage
Constant-speed motor supply

Question 24: A 4-pole DC generator has 500 armature conductors connected in 2 parallel paths (wave winding). If the flux per pole is 0.02 Wb and speed is 1200 rpm, what is the generated EMF?

100 V
150 V
200 V
400 V

Question 25: As load current increases on a DC shunt generator, the terminal voltage:

Increases sharply
Decreases slightly
Stays perfectly constant
Becomes zero

EXAM CARD BASIC

Questions25

Time limit38 min

Pass score70%

Code editionNEC 2023

DifficultyIntermediate

Last reviewedJun 2026

Timer starts immediately. Progress is auto-saved.

Source: NEC 2026 (NFPA 70)