Clarity on the 60Hz to 50Hz De-rating
Clarity on the 60Hz to 50Hz De-rating
(OP)
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
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





RE: Clarity on the 60Hz to 50Hz De-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.
RE: Clarity on the 60Hz to 50Hz De-rating
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
RE: Clarity on the 60Hz to 50Hz De-rating
Generally you are safe at the same current at 50 Hz as at 60 Hz.
Bill
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