single phase grid to 3 phase mill

[(unknown)]

I am looking for info. I want to power a water heater for radiant floor heat.

When connecting a 3 phase induction motor to the single phase grid,

the third leg will be generated, right? (I use a 25hp motor as a rotary phase

convertor for my machine shop)

Should each leg be connected to it's own heating element?

Will I burnout the third leg?

Or would a single phase motor be better for a single phase grid?

I am not really concerned with storing or selling electricity.

[Flux]

Tricky one, I think you will have fun.

The grid will supply mag current and the thing will generate 3 phase as you say but it will generate at effectively constant voltage so the heaters will work at constant power rather than follow the power dictated by wind speed.

I see it running as a phase converter converting your single phase power to 3 phase into resistors. You will have to deal with the load resistors to track the power available from the wind to try to get the loading to the heaters from generated power rather than converted from the single phase.

You may do better with capacitor excitation and forget the grid. That way you may be able to work it at variable frequency with the volts rising in volts/cycle mode and get at least a square law match to the wind.

Whatever you do I suspect it will be messy and the control scheme will not be simple.

Have fun.

Flux

[Sly]

Hi Flux,

"You may do better with capacitor excitation and forget the grid. That way you may be able to work it at variable frequency with the volts rising in volts/cycle mode and get at least a square law match to the wind"

Are you referring to your load matching scheme? If so I inquired in your diary if you had done more testing on this. I'll visit there to see your comments.

Tks

Sly

[Flux]

No not specifically. I just don't see any real chance of using balanced 3 phase heating with a single phase grid excited asynchronous generator without a lot of problems.

Using capacitor excitation lets the thing determine its own frequency and the exciting current from the capacitors will rise with frequency. The voltage for a given magnetising current will also rise with frequency so the thing might be able to track the load better. I still think it will be a difficult scheme to deal with and it wouldn't be my choice over a synchronous alternator especially as it will need gearing to a much higher speed for a low pole number machine.

Even if you can get it up to 50 or more Hz it will take a lot of capacitance I have never found capacitors to be the worlds most reliable things or the cheapest.

It would need a bit of ingenuity to keep the resistor loading correct. If the load is too small the magnetising current becomes excessive and it saturates the iron and heats the windings. Too low a resistor and it will loose excitation which may be even nastier.

I haven't looked at that diary entry for years so if you have left comments there, sorry I wouldn't have seen them. I will try to find it when I have time.

Flux

[Flux]

Just replied to the diary entry.

Flux