Motor Heat Load Dissipation

[tt90lrb]

Looking for a formula to calculate motor heat load dissipation. I have a 100hp TEFC motor (460V 3ph) on our shop floor running continuously under normal load. In sizing a ventalaion system for this area, I'm trying to account for the heat generated by the motor.

 

[mdonner]

Heat load Q = shaft power divided by motor overall efficiency(nameplate data). If nameplate data is not available and you can messure active power (or current and PF from which active power is calculated), the active power is Q.
If the load is located outside the ventilated space than subtruct the shaft power (actual or 100HP, from load Q.
If the motor's cooling is modified to external blower with piping routed outdoors, this is further reduced to neer zero.
Note: do not forget to convert units (HP<->KW<->BTU/Hr)

 

[dpc]

A 100 hp motor should have an efficiency of at least 90%. So the maximum input power will be about 111 hp at full load.

So 11 hp or about 8.2 kW is lost, by various means, as heat. This does not include losses in whatever the motor is turning, which will usually be less efficient than the motor.

A new premium efficiency motor could have a much higher efficiency, perhaps up to around 93%, depending on speed, enclosure, etc.

 

[jbartos]

Suggestion: The previous posting indicate an example that results in 8.2kW as heat loss. The actual heat loss will be smaller since there is some wattage needed for the cooling proper, and rotor dynamic air friction.