125 VDC ground fault on MK-VI GT


Thread Starter


We have 125 VDC ground fault on our GE Fr 7FA MK-VI GT. The +ve bus voltage came down to 14 VDC from a normal voltage of 62 VDC.
Efforts were made to check the integrity of field instruments and limit switches etc whichever can be done online, but found nothing. It may take couple of days to shutdown the machine for further offline checks. The query is whether is it ok to run the machine with this condition? Now the DC voltage is further found to be decreasing with time (1 V/ day approx). Till which voltage level of the DC bus, the machine can be in service?

Thanks in advance
SR Mak
You can run indefinitely so long as you take the risk. In the worst case all it takes is a -ive bus fault and you short out your MKVI power supply. In this case you would run down with whatever motors are fail safe running. Depending were the faults are you may just lose a PDM fuse which will lose power to the io modules on that circuit. Your fault could be external to the MKVI, it can be in battery chargers, protection panel, excitation panel etc ...

Best practice would be not to start with a ground fault, but in your case to shutdown as soon as possible and repair.