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Topic Title: Power Stations
Topic Summary: Electricity powered power stations?
Created On: 24 September 2013 12:33 PM
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 24 September 2013 12:33 PM
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Woodstockwood

Posts: 2
Joined: 24 September 2013

This has been puzzling me for some time ... Why (once the turbines are turning and power generation has commenced) can't an electricity power plant power itself from some of the energy it produces? I'm sure the answer is in rudimentary physics (which is clearly not my strong suit!). I would be grateful if someone could give me a brief reason. Thanks
 24 September 2013 01:14 PM
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ectophile

Posts: 548
Joined: 17 September 2001

It depends what you mean by "power itself".

There's no reason why a power station can't power all the lighting, heating, etc. required in the power station. It could also provide the power to run all the generator control systems.

The power station couldn't provide the motive power to turn its own generators, though. That requires an external source of energy - coal, gas, nuclear, running water or whatever. The reason is quite simple - it requires power to turn the generator. If you allow for friction and other losses, the amount of mechanical power needed to spin the generator is always greater than the electrical power you get out.

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S P Barker BSc PhD MIET
 24 September 2013 05:32 PM
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Woodstockwood

Posts: 2
Joined: 24 September 2013

Thanks for replying ectophile . . .

It was the turning of the generators part that I was thinking about (and the basic physics); whether electrically powered generators could (ever) provide more energy than needed to power them. I guess not!

Thanks again . . .
 24 September 2013 06:20 PM
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Zuiko

Posts: 521
Joined: 14 September 2010

I guess you are thinking why any machinery cannot run at 100% or greater effeciency (perpetual motion).

If you think about it in those terms, then the answer becomes evident (and obvious).
 25 September 2013 08:27 AM
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ectophile

Posts: 548
Joined: 17 September 2001

You can also look at it as a conservation of energy problem. The amount of energy you put into the generator over any given period must equal the amount that comes out.

If you spin a huge generator, it will get warm. That will be a mixture of friction and electrical resistance losses. So it's losing some energy that way.

So if the amount of mechanical energy you put in equals the sum of the electrical energy out plus the heat losses, then the electrical energy will always be less than the mechanical energy.

It gets worse if you try to drive the generator using an electric motor, since that will also suffer friction and resistance losses.

In that case:-
electricity in = heat lost in motor + heat lost in generator + electricity out
or if you prefer:-
electricity out = electricity in - heat lost in motor - heat lost in generator

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S P Barker BSc PhD MIET
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