Magnetek VFD problem

[Neilgrimsley]

Let me start off saying how much i am going to appreaciate and enjoy your posts on this topic. I can use the ideas ...
i have two identical (?)presses with 100HP motors. They are being controlled with MagneTek GPD 515C-B128 drives .... One is running fine but the other is faulting out with a "DC BUS OVERVOLTAGE" fault anytime the speed decreases on the drive. Ramping up is not an issue, only when we slow it down or stop it. The DC BUS does spike in the range of 700-800 volts when it faults, so it is real ....
Any suggestions on what could be causing this? I have checked the parameters between the two VFD's but feel free to point me in that direction, if you feel I may have overlooked something. Any ideas will be greatly appreaciated.

 

[keithkyll]

Braking resistor open, or braking circuit failure inside VFD.

 

[jrwb4gbm]

+1 for what Keithkyll said. Also check the incoming AC line voltage. It may be near or above the recommended high limit.

 

[mjmorrow]

I'd say, given the age of those drives, the bus capacitors are low in value, or may be open.
As large as those drives are, the DB resistors are external, so checking them will be easy.
If they are good, I'd check the bus next. Are these in a warm environment? I once got called to
fix an older AB VFD that was in an airconditioned room after the A/C failed. Every bus capacitor was open! New capacitors had it back up with no other trouble.

 

[adel1961]

if you turning a flywheel so , check the load by measuring the current consumed through a specific speed , compare this value with the other press at the same speed , then compare the 2 current readings , then you will realize if you got more load on that flywheal , then the solution would be to check the grease system for it , or you might need to help to stop it with a mechanical pads for the brake.