Motor cooling & VFD

[Mwater]

I am interested in motor cooling.

1) What's the key component in motor (induction motor) heat generation? is it the current (amps) or the input horse power and efficiency at a specific point. I read different articles and they all mention current losses in the motor (stator and Rotor), but they don't mention if all these losses are converted to heat.

2) Also if a 50 hp motor is 90% efficient, what's the heat generated? Is it the 10% loss?

3) In addition with VFD there is a change in voltage, frequency and speed but the input current could remain the same so how that affect the motor cooling. This related to the first question; if the voltage/frequency is constant but the current change with load does this affect the fan if is speed independent.

4) In case of speed dependent or independent ventilation, what's the best setup to get the appropriate cooling?

Thanks in advance for your explanation

 

[LionelHutz]

Are you sure that wasn't 100*hp = watt loss as a rule of thumb?

10*hp gives losses which equate to a motor motor efficiency of about 98.6%. Motors are usually around 90% efficient, give or take a few %.

I'd think a multiplier around 80 might be a better rule of thumb.

 

[stabilitycore]

It seems that you are all at a LOSS. Read the first thread again and then answer. As a rule of thumb, all losses are calculated as heat related (bearings create drag/friction that have to be overcome by an electrical means, etc)as it is easier for MOST to understand. A motors fan air displacement is calculated to move a certain quantity of air over a certain area (square inches ,frame of motor with or without fins)to disipate the heat generated and keep the motor at a certain temperature while at full load (FL temperature)

As itsmoked has posted in his first thread, I agree.

If you are going to run your motor at less than 70% FL speed, then with the use of an anemometer, calculate the wind speed at full speed that the motor fan 'sucks' and passes over the motor, times the area ( back of the fan cover) and calculate the l/s,gal/min. With that knowledge, purchase an additional motorised fan (yes, a squirrel cage motor) that has the correct output and mount that on your motor to compensate for the loss in air movement over the motor due to a loss in speed.


Hope that is of some help!
;-)