VFD Motor Losses at 0Hz
VFD Motor Losses at 0Hz
(OP)
We are looking at keeping a VFD turned on but have it output 0 Hz in order to keep the motor warm without the use of space heaters. No external process conditions will turn the motor.
My assumptions are when we magnetize the motor at zero speed, we don't get the "conventional" iron losses neither we get the rotor losses, neither we get friction nor
windage losses. The only losses we have in the motor are the resistive losses in the stator.
Typically stator losses are 1-1.5% at nominal current. Magnetizing current for big motors is around 30% of the rated current, because resistive losses depend on the square of the current the losses the losses would be only .09 times 1-1.5%., which equals to .1 to .15 percent
of the rating of the motor. Any motor should be able to handle that loss and it should reduce also the thermal stress the motor.
Assuming I have a 330KW motor at 600 Amps @ 400V, that would mean the motor would only draw 0.6-0.9 Amps or 330-500 Watts worth of heat.
Can anyone confirm my assumptions are correct?
My assumptions are when we magnetize the motor at zero speed, we don't get the "conventional" iron losses neither we get the rotor losses, neither we get friction nor
windage losses. The only losses we have in the motor are the resistive losses in the stator.
Typically stator losses are 1-1.5% at nominal current. Magnetizing current for big motors is around 30% of the rated current, because resistive losses depend on the square of the current the losses the losses would be only .09 times 1-1.5%., which equals to .1 to .15 percent
of the rating of the motor. Any motor should be able to handle that loss and it should reduce also the thermal stress the motor.
Assuming I have a 330KW motor at 600 Amps @ 400V, that would mean the motor would only draw 0.6-0.9 Amps or 330-500 Watts worth of heat.
Can anyone confirm my assumptions are correct?





RE: VFD Motor Losses at 0Hz
RE: VFD Motor Losses at 0Hz
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Sometimes I wake up Grumpy.
Other times I just let her sleep!
RE: VFD Motor Losses at 0Hz
RE: VFD Motor Losses at 0Hz
RE: VFD Motor Losses at 0Hz
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: VFD Motor Losses at 0Hz
What is the delta temp of your motor when stopped? Have you got a problem with condensation or is it a possibility?
If you have one, fit heaters, it is what the are there for. It is not worth screwing up your motor for a relatively low cost.
Using an injection of DC is a solution but again, it can be difficult to maintain. Maybe there is some form of logic in the ACS800 that could bring in a timer for DC injection "pre-heat" before it starts rather than keeping it on all the time.
RE: VFD Motor Losses at 0Hz
A vector drive (using rotor position feedback) does work at 0 Hz and keeps the rotor fully fluxes. This does not overheat motors designed for vector drives (no air flow).
RE: VFD Motor Losses at 0Hz
RE: VFD Motor Losses at 0Hz
Cheers
Niallnz
RE: VFD Motor Losses at 0Hz
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: VFD Motor Losses at 0Hz
It does sound interesting but are you able to alter the flux reference 'on the fly'? as I would imagine what Zcarisfast requires at zero Hz is probably quite different to what is required for 'normal' running.
RE: VFD Motor Losses at 0Hz
Short answer is yes, you can change the flux ref on the fly.