Min Fan Speed on VFD - Before Damaging
Min Fan Speed on VFD - Before Damaging
(OP)
What is the minimum fan speed I can run at using a Variable Freq. Inverter before damaging the motor. Dont you need a minimum air flow across the motor to keep it cool? I have both axial and DWDI centrif's. Motor sizes approximatly 10-30 kW. The motors ar in the air stream.
Thanks
Thanks





RE: Min Fan Speed on VFD - Before Damaging
Auxiliary fans are required when you have a constant horsepower, where you can be running 10Hz but nameplate HP. Bascially you get a doohickey that has a fan that clamps onto the motor and runs full tilt all the time. This doesn't really apply to pumps and fans.
Common in the industry are TEAO motors. THe small belly band type. We have had good luck with the more industrial type ODP motors which have built in fans. Maybe more reliable, but don't have the data. But gobs of people other than us have been using TEAO hvac duty motors with VFD's for ages. Just make sure the motor is inverter duty rated.
Check out the tech info section on the Leeson catalog (www.leeson.com)
Good luck,
Clyde
RE: Min Fan Speed on VFD - Before Damaging
Generally, I didn't see any application where you require to slow down the motor below 20 Hz.
Keeping motor in the air flow path is an added advantage in motor point of view. But strictly a no no condition when this is used for a pharmaceutical facility.
Regards,
RE: Min Fan Speed on VFD - Before Damaging
RE: Min Fan Speed on VFD - Before Damaging
As Clyde rightly pointed out, the generation of heat from the motor windings at low speeds is very low for the type of application you mentioned, ie variable fluid flow. I have tested the temperature rise of an VSD connected pump in an ambient condition of about 95F, and the results showed a decrease in winding temperature as the speed decreases (down to about 40% of full speed). Perhaps at lower speed, the temperature will start to rise again (due to magnetizing and harmonic currents), but i doubt that it will rise to a point where it will exceed the temp. rating of the insulation. From an energy conservation point of view, the savings on the motor power is minimal at lower speeds due to the cube law.