PM932VFD upgrade

[dabear3428]

Hi I too used Agis for motors 25hp to 800hp and also added DV/DT filters to VFD's with long lines. we had at least 120 VFD'S at one of the facilities.
I don't think this applies to a hobby mill, we changed a lot of bearing with EDM damage, the motor size doesn't seem to matter as much as length of line.
I don't think many hobbyist's would have any idea what the root cause of their bearing failure. "maybe just a poorly manufactured one"
Hope this helps someone.
Rich

agreed, the other issue is that for conductively coupled driven devices the rotor currents travel down the shaft and damage the bearings in the driven equipment. the insulated bearings will completely protect the motor but we have pumps and other driven equipment going out due to EDM damage, the grounding brush solves that. but we are talking about motors running 24/7 for a year for this to show up. the size of the motor or voltage does not matter as to the amount of damage or how fast it occurs, but the larger motors tend to be more expensive to fix and tend to have more consequences for down time, so I spend more $$$s making sure on them. in most cases a motor driven by a VFD in our hobby machines would last a lifetime before the damage makes itself apparent.

as to the point you made earlier about the rotor currents being present even at 60hz output, you are correct, but for any motor we plan to run at elevated hz we up the carrier freq. and that does affect it. in the case of our hobby use of VFDs i do not think anything is required for operating at lower carrier freq. and keeping close to 60hz but go very low or very high and you can run into cooling at low freq. and if the carrier freq. is upped to smooth out the wave form you may get into EDM damage at high freq. operation.

a grounding brush and a external cooling fan on a timer to run cool down after the motor is stopped could be good insurance against all of this but not required, i'm the belt and suspenders type soooo.