Synchronous Generator speed

[bartb102]

We have a hydro powerhouse with 750KW 40Hz generators with 40 poles. We cannot increase the rotor speed to produce 60Hz. power. We have been told that the stator can be rewound to produce 60Hz. It seems like this would need 1.5 stator windings per rotor pole. There is only one winding per slot, so the slots are fairly shallow. It would be much easier to restack the stator core than to modify the rotor.

Has anyone tried this? Any thoughts? A vendor has said it might be possible, but has offered no details.

 

[electricpete]

The c=3 means you cannot get a geometrically similar winding (three phases are carbon copies of each other, just shifted by 120 degrees). So you can't get a perfectly balanced fundamental. But considering the large number of poles, I think you can get veryclose. But still the harmonics would be a huge concern.

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(2B)+(2B)' ?

 

[waross]

I'm still concerned with the rotor.
How about cutting the number of poles in half on both the rotor and stator. Then slow the turbine down to get 60 Hz. Any solution will involve compromise and I suspect a reduction in the KVA rating.
Consider any one coil. The number of rotor poles passing in one revolution will induce a 40 Hz EMF. Changing the number of poles on the stator may result in some interesting harmonics but it won't change the frequency.

Bill
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"Why not the best?"
Jimmy Carter

 

[electricpete]

I'm still concerned with the rotor....Changing the number of poles on the stator may result in some interesting harmonics but it won't change the frequency.

Yes, we are in agreement.

If you wanted to produce 60hz, you would need to rewind both your stator and rotor for 60 poles

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(2B)+(2B)' ?

 

[electricpete]

How about cutting the number of poles in half on both the rotor and stator. Then slow the turbine down to get 60 Hz.

You’ll have to explain your logic.
Cutting poles in half would give 20 poles.
To get 60hz with a 20 pole machine would require you to operate at speed of 360rpm.
That’s going in the wrong direction.
The machine is currently operating at 120rpm and can’t exceed 140rpm


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(2B)+(2B)' ?

 

[waross]

I stand corrected. Sorry

Bill
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"Why not the best?"
Jimmy Carter

 

[bartb102]

Thanks for all the input, guys. The end result is that for 750KW, converting the generator to 60Hz. is not practical or cost effective compared to a inverter.