Application:
I have two pumps, a 20 Hp and a 10Hp 3/ph 460v in the same conduit.
The Vfd's are located in each mcc bucket.
I have been getting overcurrent faults on one of the Vfd's every now and then.
This just started this week, these drives have been in service for years.
So far I have taken the following steps:
Meg motor and all phases are about 7.6 Meg ohms to GND.
Line voltage is 479 phase to phase, 280 phase to GND.
With the vfd running I used a true Rms amp probe and saw A=8.3 B=6.9 C=9.3.
also at the same time I measured the voltage with a DMM and saw A-b= 320v
A-C= 327 B-C = 320
A-GND = 212
B-GND = 204
C-GND = 212
also I found that the ground does not come back to the vfd but to the common GND on the mcc and from there to the vfd.
Approximately 125ft of wire.
I replaced the drive and while I was doing this I noticed some arcing on the motor leads when I was disconnecting the leads. I assumed this was induced voltage so I held it to ground and the arcing never stopped.
I turned the pump off that was ran in the same conduit and the voltage went away (20vac).
I realize this is not the correct way to wire a vfd and that running the leads in the same conduit with no reactors or shielded cable is not ideal, but I found it strange that when I grounded the leads out that the induced voltage would not go away for at least a short time.
Also could this be the reason my original VFD failed?
I have two pumps, a 20 Hp and a 10Hp 3/ph 460v in the same conduit.
The Vfd's are located in each mcc bucket.
I have been getting overcurrent faults on one of the Vfd's every now and then.
This just started this week, these drives have been in service for years.
So far I have taken the following steps:
Meg motor and all phases are about 7.6 Meg ohms to GND.
Line voltage is 479 phase to phase, 280 phase to GND.
With the vfd running I used a true Rms amp probe and saw A=8.3 B=6.9 C=9.3.
also at the same time I measured the voltage with a DMM and saw A-b= 320v
A-C= 327 B-C = 320
A-GND = 212
B-GND = 204
C-GND = 212
also I found that the ground does not come back to the vfd but to the common GND on the mcc and from there to the vfd.
Approximately 125ft of wire.
I replaced the drive and while I was doing this I noticed some arcing on the motor leads when I was disconnecting the leads. I assumed this was induced voltage so I held it to ground and the arcing never stopped.
I turned the pump off that was ran in the same conduit and the voltage went away (20vac).
I realize this is not the correct way to wire a vfd and that running the leads in the same conduit with no reactors or shielded cable is not ideal, but I found it strange that when I grounded the leads out that the induced voltage would not go away for at least a short time.
Also could this be the reason my original VFD failed?