Temperature Derating factor 1

[Guardiano]

Hi,

I'm working in a power station where the ambient temperature is close to 55 deg C.What derating factor could be used for the loading of the generators? I know that the best way to obtain the derating factor is from the supplier but the generators are very old stuffs and I'm looking for a reasonable factor.I presume a ten degree rise in working temperature is considerable.The generators are of 5000 kVA size.

Guardiano

 

[dpc]

That's very hot. Does the generator nameplate give an ambient temperature for the rating? Normally it would be 40 deg C.

Is the generator air-cooled?

David Castor

http://www.cvoes.com

 

[wolf39]

Assuming that the old windings are of class B insulation, 120 degrees C would be the maximum operating temperature according to most standards. Therefore, at 40 degrees C ambient the permissible temperature rise would be 80 K. If the ambient temperature is 55 degrees C, then the maximum operating temperature still is 120 degrees C but the permissible temperature rise would be 65 K only. Make sure that site elevation is less than 1000 metres above sea level, otherwise the temperatures mentioned above have to be reduced.

Wolf

http://www.hydropower-consult.com

 

[dpc]

Does the generator have winding RTDs?

David Castor

http://www.cvoes.com

 

[rhatcher]

Yes, wolf39 is right. The deciding point is not the ambient temperature but the total temperature (ambient + rise). The generator's insulation temperature rise and temperature class is the deciding factor. This information should be provided on the nameplate for larger generators.

I agree with wolf39 that you will probably find that you have a Class B insulation which allows a stator temperature of 120C. This corresponds to 40C ambient + 80C rise.

If you have RTD's (dpc's question) then you can determine if your generator is running too hot.