I have used this forum before to nearly the same question, but by now I know a little more about my problem, so now I?ll try again.
In my job as an Electrical Technician I have come upon a serious problem and I hope this forum will be able to help me out.
A heat tracing hot wire had a simple ground failure, which cut off a 20A breaker along with a 100A main breaker in a 480V installation, probably because of a very high short circuit current (more than 3500A).
That was not the end of my problems. The entire high-voltage circuit (4,160V) was also cut off due to a HV ground failure.
The problem with a HV ground failure caused by a LV failure has happened before, somewhere else on this site.
The location is under Artic conditions and the grounding/bounding system, on which the 480V neutral point is mounted, is connected to a copper plate placed in seawater.
The HV grounding is connected to the same grounding/bounding system, and that might create a lot of strange paths for fault current to flow on, but that makes no sense to me. How can a high-voltage circuit identify a low-voltage ground failure?
The HV cable shield does not go through the doughnut CT, so that cannot have caused the failure.
It is an ordinary d-y transformer and the high-voltage circuit has been controlled for failures.
The relay is a Westinghouse type (50/51N instantaneous relay) being calibrated every 2 years.
What could be the reason for the above HV ground failure?
I will be patiently waiting in anticipation of hearing from you.
Thanks,
Lars
In my job as an Electrical Technician I have come upon a serious problem and I hope this forum will be able to help me out.
A heat tracing hot wire had a simple ground failure, which cut off a 20A breaker along with a 100A main breaker in a 480V installation, probably because of a very high short circuit current (more than 3500A).
That was not the end of my problems. The entire high-voltage circuit (4,160V) was also cut off due to a HV ground failure.
The problem with a HV ground failure caused by a LV failure has happened before, somewhere else on this site.
The location is under Artic conditions and the grounding/bounding system, on which the 480V neutral point is mounted, is connected to a copper plate placed in seawater.
The HV grounding is connected to the same grounding/bounding system, and that might create a lot of strange paths for fault current to flow on, but that makes no sense to me. How can a high-voltage circuit identify a low-voltage ground failure?
The HV cable shield does not go through the doughnut CT, so that cannot have caused the failure.
It is an ordinary d-y transformer and the high-voltage circuit has been controlled for failures.
The relay is a Westinghouse type (50/51N instantaneous relay) being calibrated every 2 years.
What could be the reason for the above HV ground failure?
I will be patiently waiting in anticipation of hearing from you.
Thanks,
Lars