Over Heating of Insulation Class F Motor

[Wasim A Khan]

Im having a 200HP motor running at 286 A, 3P,415VAC. This motor is designed for 50 Deg C ambient with Insulation class F for Instrument Cooper Air compressor. Motor winding temperatures are 150 deg C, and bearing temperature is 106 C at 41 C ambient temperature. I expect temperature to rise approx 160 C at ambient 50 C. Is it safe to run this motor at 150 or 160 Deg C.
My supplier is saying that it is safe to run this motor at 160 C.
We have other two instrument air compressors of same model and capacity. their winding temperature do not exceed 135 C at ambient 50 C and motor current do not go beyond 270 amps.
Any of member would help me with standards that this motor is talking more current and its winding temperature are too high, which might reduce motors life.

 

[weressl]

Im having a 200HP motor running at 286 A, 3P,415VAC. This motor is designed for 50 Deg C ambient with Insulation class F for Instrument Cooper Air compressor. Motor winding temperatures are 150 deg C, and bearing temperature is 106 C at 41 C ambient temperature. I expect temperature to rise approx 160 C at ambient 50 C. Is it safe to run this motor at 150 or 160 Deg C.
My supplier is saying that it is safe to run this motor at 160 C.
We have other two instrument air compressors of same model and capacity. their winding temperature do not exceed 135 C at ambient 50 C and motor current do not go beyond 270 amps.
Any of member would help me with standards that this motor is talking more current and its winding temperature are too high, which might reduce motors life.

What is the nameplate current of the motor? It seems like an oddball as if it is metric, then it would be 220HP.

The derating from 40 to 50 centigrade would be .92. I would expect your temperature to rise to be higher than 160C. (The temperature curve is not linear.)

Only the manufacturer can tell you what temperature rise would be within the design parameters of the specific motor. Some manufacturers allow higher rise than others, but at the cost of insulation thermal life. Nor do they all use the same insualting material, so the one who allows a higher rise may still have the longest service life. Lacking specific temperature information from the manufacturer the current is the best indication weather your motor is oveloaded or not.

In general Class F insulation is designed for 80K(Delta), so your 50C starting temperature would be roughly 323K and the maximum allowable temperature would be 403K or 130C.

So it seems like your motor is already overloaded.

Technically you can overload your motor, unless you are in a hazardous area, but there is a price to pay. The motor will burn out and the bearing will seize, not to mention the personal hazard from the hot surface. At those temperatures your motor feeders may also be exposed to temperatures beyond their limit that could results in potential shock hazard.