ee_student
New User
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- Pakistan
Can Vfds cause heating in motors at low frequency (due to the motor fan running at low speed)? If so then what should be the proposed solution?
VFDs and Heating Problems in Motors
- Thread starter ee_student
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Aleman
Senior Member
- Location
- Southern Ca, USA
The solution? Go faster! Just kidding.
I have never noticed any problems with heating and running lower speeds. I don't believe it will be an issue provided
that the motor and VFD are sized correctly for the load, and the speed is high enough that the motor doesn't stall
while running. And the motor should be rated as inverter duty.
I suppose you could mount fans to blow on the motor if it became an issue.
I have never noticed any problems with heating and running lower speeds. I don't believe it will be an issue provided
that the motor and VFD are sized correctly for the load, and the speed is high enough that the motor doesn't stall
while running. And the motor should be rated as inverter duty.
I suppose you could mount fans to blow on the motor if it became an issue.
Separately driven fan.
just the cowboy
Inactive, Email Never Verified
- Location
- newburgh,ny
If it is not a inverter duty motor it does need the external fan, most of my vfd and DC motors have one. Even inverter motors have a min speed I think.
- Location
- Illinois
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- retired electrician
Most of the motors that I have connected to VFDs were not inverter rated motors and we did not use cooling fans. The only motors that we used fans on were motors that we expected to be normally running below 50% of rated speed.
I don't think that the "inverter" rating has much to do with the cooling issue. It is mostly a higher dielectric value for the winding conductor electrical insulation.
I don't think that the "inverter" rating has much to do with the cooling issue. It is mostly a higher dielectric value for the winding conductor electrical insulation.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
There is no simplistic answer. Some motors, ie TENV (Totally Enclosed Non Ventilated) are designed to dissipate heat through their case and shaft(s). Although the harmonic content of a PWM output from a VFD is higher than if it were not from a VFD, the heating effect this has is usually not a problem for those motors. If it's a TEFC or ODP design where there is an internal fan, as the motor slows so does the fan and the cooling capacity is lost. But then if the load is centrifugal, such as a pump or fan, then the mitigating factor is that the mechanical LOAD on the motor will decrease at the CUBE of the speed change. So if you are running a motor for a centrifugal pump designed for 60Hz and the VFD turns the speed down to 25% (15Hz), then the LOAD on that motor becomes roughly 6% of what the motor was sized for (affinity law, 25% cubed). So even though you have lost fan cooling, you are at the same time putting almost NO load on that motor.
The remaining problems then come into having a TEFC, ODP or otherwise fan cooled motor used on a constant torque application at very low speeds. For those, you must use the externally powered constant speed cooling fan. Some "inverter duty" motors include it, especially if the motor says is has a 1,000:1 speed range, but it is an option, not a design requirement.
The remaining problems then come into having a TEFC, ODP or otherwise fan cooled motor used on a constant torque application at very low speeds. For those, you must use the externally powered constant speed cooling fan. Some "inverter duty" motors include it, especially if the motor says is has a 1,000:1 speed range, but it is an option, not a design requirement.
ControlsGuyWA
Member
- Location
- Port Angeles, WA, USA
With standard TEFC motors (probably ODP too but i have rarely been around those), you will usually start having your VFDs nuisance trip (motor overload fault) if running below 10 - 15Hz for extended periods of time. Above that it is usually not an issue.
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