World of Electric generators
Applied Physics
Niko Puhakka
Matti Levo
12.11.2014
First electric generator
In short, in the presence of an electromagnetic field a current can move a wire and a wire movement can generate a current.
This reversed principle (Faraday's law of induction) was discovered in 1831 by Michael Faraday and as a matter of fact he discovered the operating principle of electromagnetic generators.
Faraday built the first electromagnetic generator, called the Faraday disk, a type of homopolar generator, using a copper disc (instead of the wire) rotating between the poles of a horseshoe magnet.
When the disc was rotated by a handle the apparatus produced a small DC voltage between its hub and rim.
(http://www.juliantrubin.com/bigten/electric_motor_generator.html)
Generators in general
In electricity generation, a generator is a device that converts mechanical energy to electrical energy for use in an external circuit. The source of mechanical energy may vary widely from a hand crank
to an internal combustion engine. Generators provide nearly all of the power for electric power grids.
The reverse conversion of electrical energy into mechanical energy is done by an electric motor, and motors and generators have many similarities. Many motors can be mechanically driven to generate
electricity and frequently make acceptable generators.
(http://en.wikipedia.org/wiki/Electric_generator)
How does it work?
Explanation of how the electric generator and motor work:
https://www.youtube.com/watch?v=NSqu_u7nYU0
Generator types
There are a lot of different kind of generators, because generators are used for different processes to change mechanical energy into electrical energy. The most common generators types are:
Direct current
homopolar generator
MDH generator
Alternating current
induction generator
linear alternator generator
variable speed constant frequency generators
Equivalent circuit
An equivalent circuit of a generator and load is shown in the diagram below. The generator is represented by an abstract generator consisting of an ideal voltage source and a internal resistance.
The generator's Vg and Rg parameters can be determined by measuring the winding resistance, and measuring the open-circuit and loaded voltage for a defined current load.
Picture 1: Equivalent circuit of generator
Where do you use generators?
You use them in the process to transform different forms of energy in to electrical energy. Basically every power plant has a generator for converting the form of energy.
Many renewable energy efforts attempt to harvest natural sources of mechanical energy (wind, tides, etc) to produce electricity. A problem with some renewable energy sources is that they are not
too efficient, e.g. wind power, or at least with current energy harvesting methods.
Common use cases:
Roadway vehicles
Bicycles (dynamo)
Solar Cell
Genset
Mechanical measurement
Simple example of dynamo use case
The dynamo is an example of an electric generator. And this principle is used on bicycles for the light. So the dynamo turns the energy of the wheel (mechanical energy) into electric energy
for the light for the bicycle. And when the wheel stops turning the light stops burning in the first types of the dynamo.
Energy sources
As mentioned earlier, generators require energy in order to produce electricity. This energy can come from several different sources. When talking about electricity production in power plants,
energy resources can be roughly divided into the following categories: renewable energy resources, fossil fuels and nuclear energy sources. Out of these options, fossils fuels provide the most
of primary energy for human beings, however, since fossil fuels are not an infinite resource and nuclear power produces dangerous waste, renewable energy sources are the current focus.
Renewable resources
Wind power
Wind power is a form of solar energy. Winds are caused by the uneven heating of the atmosphere by the sun, the irregularities of the globe’s surface and rotation of the globe. Wind flow,
or motion energy, can be used to generate electricity (or mechanical power also) by using modern wind turbines. Because of our focus is the electric generators and producing the electricity,
we won’t deal with other use than electricity producing.
Wind turbines convert the kinetic energy in the wind into mechanical power, which can be used for specific tasks (e.g pumping water) or a generator can convert it into electricity. Simply stated,
a wind turbine is the opposite of a fan. Instead of using electricity to make wind, like a fan, wind turbines use wind to make electricity. The wind turns the blades, which spin a shaft, which connects
to a generator and makes electricity. That’s simple.
Picture 2: Basic structure of the wind turbine
How is the outcome power of a windmill controlled?
Windpower differs from the traditional production of electricity, because of temporal changes. The production of wind electricity changes daily and hourly based on the rate of wind. Because of this
variability in the production of wind electricity, the stability of the electric grid needs to be handled by regulating it with other production plants.
In the Nordic countries the outcome power of the windmills are controlled with hydropower, but the production variability of wind power could also be handled by regulating the power of other
power plants in the power grid. When it blows a lot, water can be stored to tanks and use it for creating the electricity when wind is low. The regulation of outcome power of the wind turbines
occurs also by selling and buying the electricity from abroad.
Picture 3: General layout of electricity network: how the power plants are connected to the electric power grid.
Related subjects
Electromagnetic induction
Faraday’s laws
References
Michael Faraday: The Invention of the Electric Motor and Electric Generator. 2014. Michael Faraday: The Invention of the Electric Motor and Electric Generator. [ONLINE] Available at:http://www.juliantrubin.com/bigten/electric_motor_generator.html. [Accessed 12 November 2014]
Electric generator - Wikipedia, the free encyclopedia. 2014. Electric generator - Wikipedia, the free encyclopedia. [ONLINE] Available at:http://en.wikipedia.org/wiki/Electric_generator. [Accessed 12 November 2014]
Kimitoön – Kemiönsaari. 2014. Kimitoön – Kemiönsaari. [ONLINE] Available at: http://www.kemionsaari.fi/asuminen-ja-rakentaminen/tuulivoima/taustatietoa/. [Accessed 12 November 2014]
Tuulivoima | Energiateollisuus. 2014. Tuulivoima | Energiateollisuus. [ONLINE] Available at: http://energia.fi/energia-ja-ymparisto/energialahteet/tuulivoima. [Accessed 12 November 2014]
Wind Energy Basics. 2014. Wind Energy Basics. [ONLINE] Available at:http://windeis.anl.gov/guide/basics/. [Accessed 13 November 2014].
Picture 1: http://en.wikipedia.org/wiki/Electric_generator#mediaviewer/File:Generator-model.svg
Picture 2:
http://en.wikipedia.org/wiki/Wind_turbine#mediaviewer/File:EERE_illust_large_turbine.gif
Picture 3:
http://en.wikipedia.org/wiki/Electrical_grid#mediaviewer/File:Electricity_Grid_Schematic_English.svg
