Electric motors at service factor

[dglaab]

Hi guys:

Does anyone have experience or input on running large motors @ service factor. My motor guru's say as long as I am sufficiently cooling the windings, go for it. I expect some penalty in insulation service life on the windings, but can accept that with my operating parameters IE <1000 hrs/yr.

thanks

Dan

[chemi-cool]

Your motor guru's right.

[US Iceman]

I would tend to agree with the motor shop with one caveat. This being, the motor is operated at sea level or not too much above it. My logic for this is as follows; as the elevation increases, the air density decreases. The lower air density will result in less mass flow available for motor cooling. Remember the motor fan provided for cooling only pushes CFM, which is constant. The mass flow decreases with higher elevations. And mass flow is what does the cooling.

If the operation is in the service factor and the motor is cooled by reasonably cool air then this is same principle as motors on evaporators in blast freezers. They too are often overloaded, but don't burnout because of the cooling provided by the extremely cold air.

[Segei]

Hi guys:

Does anyone have experience or input on running large motors @ service factor. My motor guru's say as long as I am sufficiently cooling the windings, go for it. I expect some penalty in insulation service life on the windings, but can accept that with my operating parameters IE <1000 hrs/yr.

thanks

Dan

Do you have high head pressue?

[dglaab]

No, we are actually running 125 psi or less. This question is more of a technical question than an operational one

thanks

[US Iceman]

Another way to look at this is by way of an example:

If the compressor requires 100 HP I would rather run a 125 HP motor with a 1.0 service factor at 100 HP rather than run a 100 motor with a 125 HP load on it (if it had a 1.25 SF).

I just made up the numbers but you see the difference.

[Segei]

I think that all el. motor designed for certain maximum load at certain maximum air temperature. If air temperature is cooler, then design temperature, you can go carefully into the service factor. Usually, we need this overload during summer operation at extremly hot air temperature.