Hi guys ...
I was talking to a mate a couple of days ago and he mentioned seeing a panel, that was controling a 3 phase 4 pole induction motor (Squril cage) so that it would work as a single phase alternator.

Now I know that a single phase motor will work as an alternator if it is grid connected and driven sutably above its slip speed but I hadnt ever heard of the config above.

I suspect that one, or possibly two, of the windings is/are being used to induce an exitation current in the cage whilst the final one provides single phase output but I cant figure out how that would work.

I just aquired an engine and had started looking for a 4 pole alt but finding a 3 phase motor will be far easier and cheaper.

Any thoughts anyone ....

 

http://www.who.int/management/InductionGenerators forSmallHydroSchemes.pdf


Have you read this paper?

 

Dyslexicbloke,
Your problem seems to be similar to mine but you were saying that you wanted to run your generator in island mode and I need to connect mine to the grid. I found a very good research paper called "Economic Delivery of Single Phase Power for Remote Areas Through Three Phase Self Excited Induction Generator" by "Goel,Srivastava,Swami and Negi" that describes how to connect two capacitors similar to the paper shown in the post above but the capacitor is in series with the load instead being in parallel. It is shown in the paper how to select the capacitances and they have figured out that the value of the series capacitance is approximately three times the shunt capacitance. The safe power output that the three phase induction generator can deliver to the single phase load is approximately 84 percent of it's rated capacity.
If you don't have access to the paper, if you send an email with your email address to my account then I will send it onto you.
Declan

 

Interesting stuff guys thanks.
I spent some more time searching the web after I posted the question and found the C-2C configuration and several documents simmilar to the link above.

What all the systems I found had in comon was a balest load, which I realy dont want to employ. I will be running from an engine with heat recovery in place which makes the end game a CHP installation.

When its running simply for heat a balest will be in place and will be in the form of a water heating elliment but when I am running for power, particulaly if my heat store is fairly well charged, a balest would be seriously ineffriciant.

I was hoping to find some way of dynamically controlling the capacitors, or even simply switching diferent values in and out as needed.

Looking at the info I have found thus far it appears that running at slightly above 50Hz will make things more efficiant and reduce the required Cap values.

I have been trying to work out if applying a PWM control strategy to the caps directly would work but cant find anything.

With respect to a single phase grid connected system I think its as simple as running your machine 3-5% above its synchronous speed. That is with a positive slip value.

For a 4 pole 1440 RPM machine with a 4% full load slip (1500 Synchronous) that would be circa 1560 RPM.

That said if yoiu are doing this in the UK there are regs to considder that are in place to protect thee grid and your installation.
G83 MCS I think ..... you wouldnt want to fall foul of that.

Al

 

Dyslexicbloke,
I found a very good research paper called "Economic Delivery of Single Phase Power for Remote Areas Through Three Phase Self Excited Induction Generator" by "Goel,Srivastava,Swami and Negi" that describes how to connect two capacitors similar to the paper shown in the post above but the capacitor is in series with the load instead being in parallel. It is shown in the paper how to select the capacitances and they have figured out that the value of the series capacitance is approximately three times the shunt capacitance. The safe power output that the three phase induction generator can deliver to the single phase load is approximately 84 percent of it's rated capacity.
If you don't have access to the paper, if you send an email with your email address to my account then I will send it onto you.
Declan

Dear Dec335,

Could you pls. upload the above paper on the thread for the benefit of all OP's..Thanks.

Regards,
Shahvir

 

I havnt found the one mentioned above but thereis good practical and technical info here:-
http://www.eee.nottingham.ac.uk/picohydro/docs/impman(ch9).pdf

I have another link somwhere with a deeper technical explanation ... I will have a dig about for it.

Still cant find anything that offers a control solution without a balest though.

Al