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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.
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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)
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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
generate electricity and frequently make acceptable generators.
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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
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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.
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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 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.
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Picture 3: General layout of electricity network: how the power plants are connected to the electric power grid.
How do light and matter interact when considering generators?
Understanding the meaning of light:
Light interacts with matter in 4 ways: emission, absorption, transmission and reflection or scattering.The interaction between light and matter determines the appearance of everything around us.
Light is a wave of electric and magnetic field where electrons and ions create electric fields. Those electromagnetic waves interact with matter, which contains charges (electrons), and these get pushes and pulled by the oscillating electric field. This motion may absorb or scatter the electromagnetic wave.
Picture 4: How light and matter interact in basic dynamo generator
Solar power and light
Good example about how light and matter interact in our case is the solar power generator. Solar (or photovoltaic) cells convert the sun’s energy into electricity. Whether they’re adorning your calculator or orbiting our planet on satellites, they rely on the the photoelectric effect: the ability of matter to emit electrons when a light is shone on it.
Silicon is what is known as a semi-conductor, meaning that it shares some of the properties of metals and some of those of an electrical insulator, making it a key ingredient in solar cells. Let’s take a closer look at what happens when the sun shines onto a solar cell.
Sunlight is composed of miniscule particles called photons, which radiate from the sun. As these hit the silicon atoms of the solar cell, they transfer their energy to loose electrons, knocking them clean off the atoms. The photons could be compared to the white ball in a game of pool, which passes on its energy to the coloured balls it strikes.
Freeing up electrons is however only half the work of a solar cell: it then needs to herd these stray electrons into an electric current. This involves creating an electrical imbalance within the cell, which acts a bit like a slope down which the electrons will flow in the same direction.
Creating this imbalance is made possible by the internal organisation of silicon. Silicon atoms are arranged together in a tightly bound structure. By squeezing small quantities of other elements into this structure, two different types of silicon are created: n-type, which has spare electrons, and p-type, which is missing electrons, leaving ‘holes’ in their place.
When these two materials are placed side by side inside a solar cell, the n-type silicon’s spare electrons jump over to fill the gaps in the p-type silicon. This means that the n-type silicon becomes positively charged, and the p-type silicon is negatively charged, creating an electric field across the cell. Because silicon is a semi-conductor, it can act like an insulator, maintaining this imbalance.
As the photons smash the electrons off the silicon atoms, this field drives them along in an orderly manner, providing the electric current to power calculators, satellites and everything in between.
Related subjects
Electromagnetic induction
Faraday’s laws
Photoelectric effect
Writers: Niko Puhakka & Matti Levo TU12H
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]
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Wind Energy Basics. 2014. Wind Energy Basics. [ONLINE] Available at:http://windeis.anl.gov/guide/basics/. [Accessed 13 November 2014].
photoelectric effect (physics) -- Encyclopedia Britannica. 2014. photoelectric effect (physics) -- Encyclopedia Britannica. [ONLINE] Available at:http://global.britannica.com/EBchecked/topic/457841/photoelectric-effect. [Accessed 03 December 2014].
How do solar cells work?| Explore | physics.org. 2014. How do solar cells work?| Explore | physics.org. [ONLINE] Available at:http://www.physics.org/article-questions.asp?id=51. [Accessed 03 December 2014
Picture 1: http://en.wikipedia.org/wiki/Electric_generator#mediaviewer/File:Generator-model.svg
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http://en.wikipedia.org/wiki/Electrical_grid#mediaviewer/File:Electricity_Grid_Schematic_English.svg
