Motor rating for VFD
Motor rating for VFD
(OP)
I have an ABB 30kw VFD ACS550 380V, I am in the process of specifying a motor, can I use a standard 30kw motor or would I need an increased motor kW rating ie 37kW. What do I need to consider?
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RE: Motor rating for VFD
The VFD does things with voltage that can be improved/protected with a VFD motor but that isn't generally improved in just a higher kW.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Motor rating for VFD
RE: Motor rating for VFD
Power rating: Before PWM, it was common practice to use overrated motor because the harmonics contents in motor voltage was quite high. Modern inverters do not give you that problem. So you should not need to overrate the motor.
But then, there is the cooling that usually get worse when speed is reduced. So, if you plan to run below half speed with a shaft mounted cooling fan, you had better check with the manufacturer. Which is a good idea in any case.
Also: Remember the bearing problems. They can be quite nasty in this power range. Especially with floating loads.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Motor rating for VFD
Consider following things:
1. Constant or quadratical torque
2. Speed range.In very low frequencies,some IR-compensation might be needed and at high speeds, ie. above fwp., especially friction and windage losses will be increased significantly. Keep in mind also lubrication intervals.
3. Usually at voltages below 500 V, special wire or special insulation is not needed. Recommendations varies.
4. Insulated N-end bearing could be worthwhile,even they are not always recommended for motors in this range.
RE: Motor rating for VFD
Additionally pay attention in cabling and grounding to avoid bearing currents.
RE: Motor rating for VFD
You must also consider cooling issues if the motor is to be operated loaded below about 1/3 speed. You may have to switch to an auxiliary-cooled motor if you are operating heavy loads at slower speeds. Your motor manufacturer can give you speed-load profiles for your motor.
Finally, given the motor's continuous current at the expected continuous load plus the motor's peak current at the load's peak torque requirement, check your drive to be sure you have enough ampacity both continuous and short-term peak to cover the motor's requirements. If the drive has more, you are ok. If the drive has less, the drive is not big enough for the job. If the drive has exactly what your motor needs, why then, you are having an incredibly lucky day!