IntroductionAs its name suggests, a generator generates electricity. Michael Faraday's

discovery of electromagnetic induction demonstrated a way to construct a simple

generator, but there was little need for such a device until commercial

technologies that used electricity, such as lights, appeared. The earliest

commercial uses of electricity, such as telegraphy, arc lighting systems, and metal

electroplating used batteries as their power source. This was a very expensive

way of generating electricity.

What is a DC Generator

A DC generator is a machine that converts mechanical energy into

direct current electrical energy.

A longer answerA DC generator is an electrical machine which produces direct current electricity. It

must be turned by a prime mover which can be an internal combustion engine -

driven, usually, by diesel oil or gasoline - or can be a turbine, driven either by

superheated steam or by water falling from a reservoir. (The latter is known as

"hydro-electric power generation").

HistoryThis model of a direct-current generator was designed by Elihu Thomson to

produce a constant voltage. It could also be used as a motor that would maintain a

constant speed. It came to the Smithsonian from the U. S. Patent Office,

representing patent number 333,573, issued to Thomson on January 5, 1886. The

patent itself indicates that no model was submitted (which is not surprising since

by that time models were not required), and this example was probably given to

the Patent Office at a slightly later date for display purposes.

Thomson and Edwin Houston were school teachers in Philadelphia in the 1870s

when they formed a partnership (the Thomson-Houston Company) to enter the

new and competitive arc-lighting field. They produced a number of successful

generators, motors, meters, and lighting devices. Most of their system employed

alternating current, which was as good as direct current for lighting. With the

development of the transformer in the mid-1880s, AC systems assumed added

importance because electricity generated at a low voltage could now be converted

to high voltage for more efficient transmission and then converted back to safer

low voltage for use by consumers. But electro-chemical applications (like plating)

required DC generators, and, until the invention of a practical AC motor by Nikola

Tesla at the end of the 1880s, street railways depended on DC.

Thomson-Houston merged with Edison's company in 1892 to form General

Electric.

Principle of DC Generator

There are two types of generators, one is ac generator and other is dc generator.

Whatever may be the types of generators, it always converts mechanical power to

electrical power. An ac generator produces alternating power. A DC generator

produces direct power. Both of these generators produce electrical power, based

on same fundamental principle of Faraday's law of electromagnetic induction.

Hence the most basic tow essential parts of a generator are a) a magnetic field

and b) conductors which move inside that magnetic field. Now we will go through

working principle of dc generator. As, the working principle of ac generator is not in

scope of our discussion in this section.

Single Loop DC Generator

Working Principle of DC Generator

It is seen that in the first half of the revolution current flows always along ABLMCD

i.e. brush no 1 in contact with segment a. In the next half revolution, in the figure

the direction of the induced current in the coil is reversed. But at the same time the

position of the segments a and b are also reversed which results that brush no 1

comes in touch with that segment b. Hence, the current in the load resistance

again flows from L to M. The wave from of the current through the load circuit is as

shown in the figure. This current is unidirectional.

This is basic working principle of DC generator, explained by single loop generator

model.

Applications of DC Generators

DC Generator

Department of EEE

1. Mehedi Kahhar ID: 143010001 2. Shahida Akter ID: 143010003

3. Tanjina Yesmin ID: 143010004 4. Shofiqul Islam ID: 143010006

5. Foyez Ahmed ID: 143010007 6. Abdul Kader ID: 140201113

Conclusion

A DC generator can be used as a DC motor without any constructional changes

and vice versa is also possible. Thus, a DC generator or a DC motor can be

broadly termed as a DC machine, Yoke, Poles and pole shoes, Field winding,

Armature core, Commutator and brushes,are the main parts who are working with

dc generator . From its invention period to present its developed its design and

efficiency . Generator is most essential machine to spend modern life.

Old version of DC Generator

Latest Version of DC Generator

Losses of DC Generator1. Cupper Lose

a.Armature Cu loss

b.Shunt field loss

c.Series field loss

2.Iron loss

a.Hysteresis loss

b. Eddy current loss

3. Mechanical loss

a.Friction

b.Windage

Acknowledgements can go here.

Types of DC GeneratorsGenerally DC generators are classified according to the ways of excitation of their

fields. There are three methods of excitation.

i. Field coils excited by permanent magnets – Permanent magnet DC generators

ii. Field coils excited by some external source – Separately excited DC generators

iii. Field coils excited by the generator itself – Self excited DC generators

Self-excited DC Generators

According to the position of the field coils the Self-excited DC generators may be

classified as…

A. Series wound generators

B. Shunt wound generators

C. Compound wound generators

There are various types of DC generators available for several types of services.

The applications of these dc generators based on their characteristic are discussed

below:

Applications of Separately Excited DC Generators

I. Because of their ability of giving wide range of voltage output, they are generally

used for testing purpose in the laboratories.

II. Separately excited generators operate in a stable condition with any variation in

field excitation. Because of this property they are used as supply source of DC

motors, whose speeds are to be controlled for various applications. Example- Ward

Leonard Systems of speed control.

Applications of Shunt Wound DC Generators

I. They are used for general lighting.

II. They are used to charge battery because they can be made to give constant

output voltage.

III. They are used for giving the excitation to the alternators.

IV. They are also used for small power supply.

Applications of Series Wound DC Generators

I. They are used for supplying field excitation current in DC locomotives for

regenerative breaking.

II. This types of generators are used as boosters to compensate the voltage drop

in the feeder in various types of distribution systems such as railway service.

III. In series arc lightening this type of generators are mainly used.

Applications of Compound Wound DC Generators

I. Cumulative compound wound generators are generally used lighting, power

supply purpose and for heavy power services because of their constant

voltage property. They are mainly made over compounded.

II. Cumulative compound wound generators are also used for driving a motor.

III. For small distance operation, such as power supply for hotels, offices, homes

and lodges, the flat compounded generators are generally used.

Magnetization Curve of DC Generator

The derivation of EMF equation for DC generator has two parts:

1. Induced EMF of one conductor 2. Induced EMF of the generator

Derivation for Induced EMF of One Armature Conductor For one revolution of the conductor, Let Φ = Flux produced by each pole in weber (Wb) and P = number

of poles in the DC generator therefore, Total flux produced by all the poles And, Time

taken to complete one revolution Where, N = speed of the armature conductor in rpm

Now,according to Faraday’s law of induction, the induced emf of the armature conductor is denoted by

“e” which is equal to rate of cutting the flux. Therefore,

Induced emf of one conductor is

Derivation for Induced EMF for DC Generator Let us suppose there are Z total numbers of conductor in a generator, and arranged in such a manner

that all parallel paths are always in series. Here, Z = total numbers of conductor A = number of parallel

paths Then, Z/A = number of conductors connected in series We know that induced emf in each path is

same across the line Therefore, Induced emf of DC generator E = emf of one conductor × number of

conductor connected in series. Induced emf of DC generator is Simple

wave wound generator Numbers of parallel paths are only 2 = A Therefore, Induced emf for wave type

of winding generator is Simple lap-wound generator Here,

number of parallel paths is equal to number of conductors in one path i.e. P = A Therefore, Induced emf

for lap-wound generator is

EMF Equation of DC Generator

Magnetization curve of a DC generator is that curve which gives the relation between field

current and the armature terminal voltage on open circuit. When the DC generator is driven by a

prime mover then an emf is induced in the armature. The generated emf in the armature is given

by an expression

is constant for a given machine.it is replaced by K in this equation.

Here, φ is the flux per pole, P is the no. of poles, N is the no. of revolution made by armature per

minute, Z is the no. of armature conductors, A is no. of parallel paths.

GREEN UNIVERSITY OF BANGLADESH