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I am a pure physics guy, so I understand the fundamental processes behind the generation of electricity, but I'd like to know how to apply it. I was wondering what kind of methods were used in the industry in terms of the generation of electricity.

Is DC generated using a sort of faraday disk generator? How is AC generated? Are there any good books on the subject?

I am capable of handling technical writing and math doesn't scare me.

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    \$\begingroup\$ Wikipedia: "electricity generation" has a good overview. \$\endgroup\$ – davidcary Aug 20 '12 at 19:36
  • \$\begingroup\$ Btw what David Kessner calls "Electro-magnetic" is what wikipedia calls "Electromagnetic induction". \$\endgroup\$ – Johan Aug 21 '12 at 7:32
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Electricity is made using a variety of processes:

Electro-magnetic: This is something that takes mechanical motion and converts it to electricity. The common way this is done is with a generator that is turned using a steam turbine from a coal or nuclear power plant. But it could also be a hand-cranked generator, a car alternator, or even one of those "shake to charge" flashlights.

Electro-Chemical: This is a basic battery-- both rechargable or normal batteries. The electrical energy is released from a chemical process.

Thermo-electric: When you get two dissimilar metals and you heat up one side and cool another an electrical current is generated. I can't possibly explain this one very well so here is the Wikipedia link.

Photovoltaic: A solar cell. Converts photons directly into electricity.

Electrostatic: Basically, using static electricity to do something. Normally this would be a van de graaff generator. It is hard, but not impossible, to make something useful with this as an energy source.

Piezoelectric: Some materials are piezoelectric. If you strike/hit/vibrate the material it will generate a small electrical current. This technique is mainly used as a sensor rather than a power source, but there are some places where using it as a power source is becoming practical.

That's all I can think of. I'm sure there are more, but these are the main ways that electricity is generated.

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  • \$\begingroup\$ among those ways, I think only photovoltaic (solar), electro-chemical (batteries) and electro-magnetic-mechanic (all kinds of motors) are the main ways of generating power. \$\endgroup\$ – user51166 Aug 20 '12 at 20:10
  • \$\begingroup\$ @user51166 Those three are certainly the most common, but the Curiosity Rover, currently on Mars, is using Thermo-electric where nuclear decay is providing the heat for the thermo-electric generator. \$\endgroup\$ – user3624 Aug 20 '12 at 20:18
  • \$\begingroup\$ interesting, didn't know that. Good example \$\endgroup\$ – user51166 Aug 20 '12 at 20:22
  • \$\begingroup\$ You left out thermionic. That's when you heat something to high enough temperature electrons are sortof boiled away. You could get a measurable voltage accross old vacuum tube diodes sometimes, especially if you cranked up the cathode heater a bit. There have been thermionic generators that powered spacecraft, with the heat source usually being radioactive decay of strontium 90. +1 anyway for a good overview. \$\endgroup\$ – Olin Lathrop Aug 21 '12 at 1:41
  • \$\begingroup\$ I think Electro-magnetic is the method behind something like 95-99% of the global electrical production. All powerplants that uses some kind of "physical movement to electricity" uses this, so that would be Coal, Natual gas, Nuclear, Water, Wave, Wind, Solar power tower, etc etc etc. \$\endgroup\$ – Johan Aug 21 '12 at 7:25
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In short: most of the electricity is generated as AC (sine wave).

There are several possibilities (for a more complete reading you may want to search wikipedia for instance):

  • Synchronous motor: used with turbines from water barrages / nuclear turbines / gas turbines / vapour turbines (basically any turbine that turns as an effect of a flow of a fluid, be it either gas or liquid). A bit less known is the usage of synchronous motors in the field of wind energy (basically you get a variable axe/turbine speed v_turbine = f(wind), therefore in order to generate coherent 50Hz/60Hz you need to do a two step conversion: AC - - (rectifying) -> DC - - (inverter) - > AC (50Hz/60Hz)
  • Asynchronous motor: used often with wind turbines.
  • DC motor: not much used anymore AFAIK (at least not for large-power production)
  • Solar energy: generates DC energy (or at least pseudo-DC, i.e. DC if you consider that the voltage's / current's variation is pretty slow)

Not sure if I forgot something important. Most energy is produced by synchoronous motors. Therefore the power frequency (50Hz/60Hz) is REALLY important in order to keep all alternators in sync. A variation of <1Hz is able to cause enormous black-outs! Recently renewable energies introduced DC energy as a new source of energy, as well as asynchronous motors in wind energy production.

DC is nowadays generated using semiconductors: diodes, thyristors and transistors basically. The easiest one are the diodes (automatic AC/DC conversion), thyristors are a bit less used nowadays (still very used at high power/voltage levels though), while on lower voltage/power levels they've been replaced by transistors (MOSFET for low-medium power and IGBT for higher power).

A mechanical rectifier exist, though not used anymore AFAIK (maybe with universal motor: DC motors that can be directly connected to AC power plug and work correctly, not sure if that is considered a rectifier since voltages and magnetic fields are always on opposite direction, hence the force contributes to make the motor turn). See wikipedia for mechanical rectifier if you're interested.

Having presented the main sources of energy production (their contribution in % varies from country to country), now it's time for a quick overview of energy conversion:

  • AC/AC conversion: either by using of a transformer (same frequency, big, heavy, very expensive), either by using the two step AC -> DC -> AC conversion I spoke above of
  • DC/DC conversion: buck, boost, buck-boost, flyback, forward converters. The input DC voltage can be raised or lowered as you want
  • AC/DC conversion: also known as rectifier, most commonly performed by diodes or thyristors. It also exist a transistor-based rectifier (also known as an active rectifier)
  • DC/AC conversion: also known as inverter, most commonly performed by transistors (MOSFETs or IGBT). Typically it consists of two-level PWM, generating a square wave that will be filtered afterwards. This however produces a high level of harmonics which are not good for the power network. Therefore this approach is often a bit more complicated: either using > 2 PWM levels (not only 0V, +- V_peak) but with more values (for instance 0V, +-0.25V_peak, +-0.5V_peak, +-0.75V_peak, +-V_peak), or using two transformers combined with different windings types in order to get rid of some of the harmonics

Hope this clarified a little bit. Your question was a little bit too generic in my opinion. Not sure if I answered it. Feel free to ask otherwise.

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Electricity is most commonly made using AC generators (alternators). DC is mostly generated from AC.

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    \$\begingroup\$ Come on, Wouter, you can do better than this. :-) This is more like a comment. \$\endgroup\$ – stevenvh Aug 20 '12 at 19:17
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    \$\begingroup\$ I answered the question. IMO being brief has merit too (sometimes even more than being verbose). \$\endgroup\$ – Wouter van Ooijen Aug 20 '12 at 19:31
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    \$\begingroup\$ If I were OP I would have liked to know how you get the sine shaped AC, for instance, or how you get the DC from AC. A couple of 1N5401s? Nothing wrong with brief, but completeness should have priority. I got kudos yesterday for a "succinct" answer, which nonetheless was 280 words long. \$\endgroup\$ – stevenvh Aug 21 '12 at 5:23
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Electricity for industrial use is typically generated by rotary generators, which may be spun by a variety of means such as gas or diesel engines, hydro, wind, etc. Whatever can impart the necessary torque. Here are a couple of surprisingly good basic videos, offering an overview, concepts, terminology, and even some basic maths:

US Army Motors and Generators Part 1

US Army Motors and Generators Part 2

Enjoy!

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