induction motor as grid interactive generater

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induction motor as grid interactive generater

Postby eraser1 » Sat Oct 14, 2006 7:58 am

I have read that you can use an induction motor as a grid fed generater by spining it faster than the motors rated speed , Also i have read people are using 3 phase motors connected into a 1 phase system coming to the house, I am iterested to know how you would wire a single phase power supply to a three phase motor to generate power, how could it be done here in Australia we have 240 volt single phase power at 50hz.
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Postby Bob Boyce » Sat Oct 14, 2006 1:22 pm

Induction motors make so-so generators. The problem is that the speed controls the frequency more so than the output voltage. Voltage is what determines which direction the current flows in AC grid tie. Sure, speeding up a motor will cause it to generate power, but not in the way desired. The power generated will buck the phase of the AC, causing increased losses. Seperate from the AC grid, an induction motor can be used as a poor mans generator. Residual magnetism will usually allow an induction motor to begin generating as soon as a load is applied while it is rotated. Efficiency is poor however when compared to PM or even field wound generators.

A proper AC generator (or inverter) for grid tie would use phase sense to synchronize with the grid power, then raise output voltage (by increasing drive to the field windings in a generator) so that generated power flow is away from the generator (or inverter) and into the grid. Any shift in shaft speed (inverter frequency) will result in the source going out of phase and power bucking against the grid power.

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Postby Bob Boyce » Sat Oct 14, 2006 1:41 pm

Oh, forgot the 3 phase question.

A 3 phase motor can be driven from single phase with either one of 2 methods. Probably the best method is to use a start capacitor and a run capacitor. Next best method would be to connct 2 of the 3 phase wires to single phase power, then spin the shaft to start the motor. A starter pull rope wound around the shaft works well. Once spinning from either method, psuedo 3 phase power can also be drawn from the 3 phase motor connections. It is not true 3 phase, but close enough to power most 3 phase motors. This is called a rotary 3 phase converter.

Another method, that I have only seen used in hardware owned by the military, is a static 3 phase converter. It is a large toroidal transformer with a 360 degree single phase winding, and a 3 phase winding consisting of 3 seperate windings spaced 120 degrees apart on centers. Take a look at the toroidal transformer in my projects folder for an example of a static 3 phase converter. It works by creating a rotating magnetic field in the core, similar to a motor, but without a rotor. If built accurately, it can produce true 3 phase power.

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Wind Turbines

Postby ElectroGasMan » Sun Oct 15, 2006 6:19 am

Gentlemen

I must say I have learned many things as I read. One thing I might add is that for years now I have been working to understand large wind turbines. For the last 50 years regular motors were used and are still working. There must be power conditioning banks to make up for losses in varying wind speeds. Today this is out dated compared to the 99% efficent inverters out therre.

Just down the road from me in Kansas there are a bank of large turbines rated at 600 KWH each. 300 of them. When the wind is not blowing the motor turns these turbines anyway. This methode is used for producing hugh amounts of three phase electrical power without high priced syncronizing devices. Power correction factor and equiptment is what is needed instead, to use three phase motors.

Varying wind speed has always complicated things so turbines have airfoils that adjust in some form or another to compensate for large RPM swings.

This was the first methode used because of its cost effectiveness. PM motors and wound rotor are far more controllable though more expensive than simple motors.

Electrolysis could make using simple motors generating power look more attractive again.

Until next time I bid you farewell 8)
Michael in Kansas
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generator

Postby emuntinga » Fri Nov 17, 2006 3:25 am

hello,

i have a motor with stator and rotor windings. (3p)
is it possible to generate power from this motor.


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Postby 12volt dan » Sat Nov 18, 2006 2:39 pm

You bet, I know of a couple of guys that have and they work just fine. I've never done it myself though.
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generator

Postby emuntinga » Sun Nov 19, 2006 3:50 am

hello 12volt dan

can you tell me where i can find info
so i can generate power from the motor
this are the specs on the motor
specs stator
3 phase motor
^/x = 220volt/380volt
A/A = 23.5amp/15.5amp
cos = 0.78
KW/HP = 5.9/8
p.min = 950

specs rotor
rotor = 217volt / 17 amp

i can only find data from motors with a solid rotor.
thanks for the info

ernst
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Postby 12volt dan » Sun Nov 19, 2006 11:08 am

Here are some links

principal of operation http://www.windpower.org/en/tour/wtrb/syncgen.htm

here's some on using them http://www.redrok.com/cimtext.pdf

http://www.team.net/www/shop-talk/hm3phase.html

http://www.woodweb.com/knowledge_base/T ... rator.html

There are more links available, just google "3 phase moto/generator
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