# Generator

Photo by: Peter Dean

A generator is a machine that converts mechanical energy into electrical energy. Generators can be subdivided into two major categories depending on whether the electric current produced is alternating current (AC) or direct current (DC). The basic principle on which both types of generators work is the same, although the details of construction of the two may differ somewhat.

## Principle of operation

In 1820, Danish physicist Hans Christian Oersted (1777–1851) discovered that an electric current created a magnetic field around it. French physicist André Marie Amperè (1775–1836) then found that a coil of wire with current running through it behaved just like a magnet.

In about 1831, English physicist Michael Faraday (1791–1867) discovered the scientific principle on which generators operate: electromagnetic induction. By reversing the work of Oersted and extending the work of Amperè, Faraday reasoned that if a current running through a coiled wire could produce a magnetic field, then a magnetic field could induce (generate) a current of electricity in a coil of wire. By moving a magnet back and forth in or near a coil of wire, he created an electrical current without any other source of voltage feeding the wire.

## Words to Know

Alternating current (AC): Electric current in which the direction of flow changes back and forth rapidly and at a regular rate.

Armature: A part of a generator consisting of an iron core around which is wrapped a wire.

Commutator: A slip ring that serves to reverse the direction in which an electrical current flows in a generator.

Direct current (DC): Electrical current that always flows in the same direction.

Electromagnetic induction: The production of an electromotive force (something that moves electricity) in a closed electrical circuit as a result of a changing magnetic field.

Slip ring: The device in a generator that provides a connection between the armature and the external circuit.

Faraday also discovered that it makes no difference whether the coil rotates within the magnetic field or the magnetic field rotates around the coil. The important factor is that the wire and the magnetic field are in motion in relation to each other. In general, most AC generators have a stationary (fixed) magnetic field and a rotating coil, while most DC generators have a stationary coil and a rotating magnetic field.

## Alternating current (AC) generators

A magnet creates magnetic lines of force on either side of it that move in opposite directions. As the metal coil passes through the magnetic field

Serbian-born American electrical engineer Nikola Tesla (1856–1943) with one of his early electrical generators. (Reproduced by permission of
The Granger Collection, Ltd.
)

in a generator, the electrical power that is produced constantly changes. At first, the generated electric current moves in one direction (as from left to right). Then, when the coil reaches a position where it is parallel to the magnetic lines of force, no current at all is produced. As the coil continues to rotate, it cuts through magnetic lines of force in the opposite direction, and the electrical current generated travels in the opposite direction (as from right to left). The ends of the coil are attached to metal slip rings that collect the electrical current. Each slip ring, in turn, is attached to a metal brush, which transfers the current to an external circuit.

Thus, a spinning coil in a fixed magnetic field will produce an alternating current, one that travels first in one direction and then in the opposite. The rate at which the current switches back and forth is known as its frequency. Ordinary household current alternates at a frequency of 60 times per second (or 60 hertz).

The efficiency of an AC generator can be increased by substituting an armature for the wire coil. An armature consists of a cylinder-shaped iron core with a long piece of wire wrapped around it. The longer the piece of wire, the greater the electrical current that can be generated by the armature.

Commercial generators. One of the most important uses of generators is the production of large amounts of electrical energy for use in industry and homes. The two most common energy sources used in operating AC generators are water and steam. Both of these energy sources have the ability to drive generators at the very high speeds at which they operate most efficiently, usually no less than 1,500 revolutions per minute.

In order to generate hydroelectric (water) power, a turbine is needed. A turbine consists of a large central shaft on which are mounted a series of fanlike vanes. As moving water strikes the vanes, it causes the central shaft to rotate. If the central shaft is then attached to a very large magnet, it causes the magnet to rotate around a central armature, generating electricity.

Steam power is commonly used to run electrical generating plants. Coal, oil, or natural gas is burned—or the energy from a nuclear reactor is harnessed—to boil water to create steam. The steam is then used to drive a turbine which, in turn, spins a generator.

## Direct current (DC) generators

An AC generator can be modified to produce direct current (DC) electricity also. This change requires a commutator. A commutator is simply a slip ring that has been cut in half, with both halves insulated from each other. The brushes attached to each half of the commutator are arranged so that at the moment the direction of the current in the coil reverses, they slip from one half of the commutator to the other. The current that flows into the external circuit, therefore, is always traveling in the same direction. This results in a steadier current.

[ See also Electric current ; Electromagnetic field ; Electromagnetic induction ]

## User Contributions:

chaitanya
Nov 26, 2006 @ 3:03 am
The article is nice for basic understanding but will be good if formulas and drawbacks that are present in generators are given.
MD.NAJMUL HUDA
Nov 7, 2007 @ 2:02 am
i m a student of engineering .i like the description of generator principle.this helps me very much.
Ashek Ullah
Mar 2, 2008 @ 1:13 pm
Really very impotent subject matters explained very easy way.If you kindly provide more information it will be so much helpful for me.
Thank you.
Sincerely
Ashek Ullah
Jon
Jun 11, 2008 @ 6:06 am
i am an engineering student, great site, is the ac generator for three phase the same operation, if not what changes exactly?
Thank you.
Sincerely
Jon
sravan
Jul 14, 2008 @ 11:11 am
its very nice for knowing the basics of a generator and if some of the diagramatic representations are provided then it will be much good
siddartha
Jul 18, 2008 @ 5:05 am
It is really very nice description. I felt diagrammatic representation would have been better

Regard
KC
mubeen
Jan 10, 2009 @ 3:15 pm
i am realy impressed by the explanation of the ac generator thank you for making sure!!!
nea
Feb 8, 2009 @ 2:02 am
This information is very helpful to me. I am a 4th year high school and will be reporting about generators next week. Thank you for this info, i hope it would be updated for more information and more detailed.
mubashra
Mar 18, 2009 @ 1:01 am
i really feel glade to get such a basic things in a very easy and intersting manner.others basis of engineering should also provide in such manner
fendy
Apr 18, 2009 @ 9:09 am
I am a electrician and i have problem with the ac generators, the ac voltage is missing, the diode broken i alredy fix the diode but still the same. so i want to learn about how the ac generator works very well, cant you help me with my problem? please its urgent
samuel ntsiful
May 4, 2009 @ 1:13 pm
i would like to know about the principle of operation of an a.c brushless generator.
rahwa
May 5, 2009 @ 3:03 am
it is a nice clarification about the working principle of generators keep it up!
Arun
Jun 18, 2009 @ 1:13 pm
If generator the rotor only rotates ...If it posible to rotate stator also....
vidya
Aug 13, 2009 @ 12:00 am
After reading this article, i clearly understood the subject. But i require a more detailed explanation , i mean an animation will aid in better understanding.
abala emmanuel
Aug 16, 2009 @ 9:09 am
simple, understandable to the average person and comprehensive
thank you
Abala Emmanuel
nag
Aug 27, 2009 @ 9:09 am
this site is very well because iam a b.tech student
sivasatish
Sep 10, 2009 @ 6:06 am
this is very useful for all the students .it is very intresting.
upnesh
Sep 17, 2009 @ 7:19 pm
A.C Generator details find this topic and learn this topic this is very useful topic so by care and read.
Hazara Bamyan
Oct 7, 2009 @ 12:12 pm
it is great to read this and understand this...but the main question that arise on my mates mind is that;

if A.C current changes it's direction continuously..e.g back and forth then the resultant distance covered by the current will be zero..because it will be similar to vibratory motion with zero resultant.
Nafis Rahman
Nov 17, 2009 @ 7:19 pm
Thanks for a clear description of generator. For my project work and thesis i needed that.
I am an electrical engineering student form IUBAT, Bangladesh.
manish
Jan 23, 2010 @ 11:23 pm
thanks for providing a remarkable concept.this will really help the new studnet.
manish shrivastava
Aug 25, 2010 @ 10:10 am
i want to know about principle working of diesel generator.
Dec 5, 2010 @ 4:04 am
Mar 27, 2011 @ 9:21 pm
pls send to me about generators for up to date information
Jul 20, 2011 @ 11:23 pm

Thanking u