Clarity on the 60Hz to 50Hz De-rating

[ed53511]

Clarity on the 60Hz to 50Hz De-rating

I currently use a P40G4550 100HP Reliance Motor
(1800RPM - 230-460V/3Phz/60Hz - 232/116FLA - 405T Frame - 94.5 EFF)

We asked our supplier to provide this motor de-rated to 415V/3Phz/50Hz.

The new motor nameplate reads; 75HP - 1485RPM – 208/415V – 50Hz – 204/102 FLA

It is my understanding from reading the FAQ: Motors: Changing between a 50Hz and 60Hz power supply the de-rating should be 83%, and the FLA should increase.

Why did the HP drop 25%?
Why did the FLA drop?

If these adjustments are correct, what is the formula/process/equation to reach these numbers?

Thanks

 

[LionelHutz]

I'd guess the HP dropped to 75HP because that is the next lowest NEMA HP rating.

Then, the current was also dropped to reflect this under-rated HP. I calculate 209/104FLA (ratio 75/83 of original values) but then motor currents can't quite be linearly scaled and that could explain the difference.

 

[itsmoked]

Why did the HP drop 25%?

100 x 5/6 = 83HP

Why did the FLA drop?

As MR. Hutz described, HP reduction.

HP = Torque x RPM

The torque has remained similar but the RPM has dropped; (1800 - 1485)/1800 x 100% = 17.5%

Could be they are just doing the NEMA thing as previously stated.

I suspect it is the NEMA aspect mostly. Could well be they just tossed that motor onto a dynamometer, selected "75" stuck 415V to it and took the resulting FLA number.



Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Watch your supply voltage. The new nominal voltage should be 383 volts. 415 is over 8% high. That does not leave much of your 10% over voltage margin.
Generally you are safe at the same current at 50 Hz as at 60 Hz.

Bill
--------------------
"Why not the best?"
Jimmy Carter