Ground fault indication on corner ground delta system

[Kenshaffer87]

Hello, I ran into a situation that really stumped me to at work today. I was at a factory that has a 240v corner ground delta system, and they had a 3 light bulb “ground fault indicator” system, which I have seen and I understand how it works in a ungrounded delta system. But I can’t understand how this could work in a corner ground system. They swear that all 3 light bulbs stayed lit in the past but now one is out (the one on the grounded phase). Can someone explain this to me? Or are they just crazy and it never worked?

 

[GoldDigger]

What it really sounds like is that at some point it really was an ungrounded delta, which suffered a hard ground fault on one phase and instead of repairing it the responsible (?) people decided to just call it a corner grounded system and move on from there.
Since then deliberate ground bonds may have been added to the previously ungrounded phase.
Does the factory have equipment that would be very expensive to shut down without warning in the case of a ground fault? That is the primary justification for an ungrounded system in the first place, but it means that a planned partial or complete shutdown needs to be taken if necessary to repair that first ground fault, before a second ground fault shuts the place down.

 

[oldsparky52]

If the lights were wired to two separate phases each, the lights would work whether you grounded one phase or not ... right?

 

[oldsparky52]

Did you check how the lights are wired?

If so, how are they wired?

 

[GoldDigger]

If the lights were wired to two separate phases each, the lights would work whether you grounded one phase or not ... right?

But in that case they would be useless as a phase loss monitor!

 

[Kenshaffer87]

What it really sounds like is that at some point it really was an ungrounded delta, which suffered a hard ground fault on one phase and instead of repairing it the responsible (?) people decided to just call it a corner grounded system and move on from there.
Since then deliberate ground bonds may have been added to the previously ungrounded phase.
Does the factory have equipment that would be very expensive to shut down without warning in the case of a ground fault? That is the primary justification for an ungrounded system in the first place, but it means that a planned partial or complete shutdown needs to be taken if necessary to repair that first ground fault, before a second ground fault shuts the place down.

That’s a good thought, I hadn’t thought of that! I will need to see who owns/services their transformers there. Thanks!

 

[oldsparky52]

But in that case they would be useless as a phase loss monitor!

Yea, I thought about that (series circuit would keep the lights on, but two would be dimmer ) after I made my post. I still would like to know how those lights were wired.

 

[Kenshaffer87]

Did you check how the lights are wired?

If so, how are they wired?

They had each wired phase to ground (so A phase to grounding conductor, ect). So, on the bulb that was out they have the grounded phase to grounding conductor. (So no potential across the socket). So they were wired as you would expect to see for a ground fault indicator for an ungrounded delta system.

 

[oldsparky52]

They had each wired phase to ground (so A phase to grounding conductor, ect). So, on the bulb that was out they have the grounded phase to grounding conductor. (So no potential across the socket). So they were wired as you would expect to see for a ground fault indicator for an ungrounded delta system.

Makes post #2 look like the winner.

 

[Kenshaffer87]

Makes post #2 look like the winner.

I agree! Thanks for the quick responses!

 

[Jraef]

I worked at a steel mill that had an un-grounded delta system and ground lights like that. The lights told us if there was a problem somewhere, we just never knew where and had to run around in golf carts trying to find either a column of smoke or a production manager running around pulling his hair out looking for an electrician.

I left in the late 70s but went back there as a contractor in the 90s and saw that one lamp was out, indicating that it was grounded. The guys there said it had been that way for years, nobody was sure what it meant...

 

[Kenshaffer87]

I worked at a steel mill that had an un-grounded delta system and ground lights like that. The lights told us if there was a problem somewhere, we just never knew where and had to run around in golf carts trying to find either a column of smoke or a production manager running around pulling his hair out looking for an electrician.

I left in the late 70s but went back there as a contractor in the 90s and saw that one lamp was out, indicating that it was grounded. The guys there said it had been that way for years, nobody was sure what it meant...

lol, that sounds like the guys at this place, they knew it meant something, but no idea what.

 

[ptonsparky]

I worked at a steel mill that had an un-grounded delta system and ground lights like that. The lights told us if there was a problem somewhere, we just never knew where and had to run around in golf carts trying to find either a column of smoke or a production manager running around pulling his hair out looking for an electrician.

I left in the late 70s but went back there as a contractor in the 90s and saw that one lamp was out, indicating that it was grounded. The guys there said it had been that way for years, nobody was sure what it meant...

The smoke, flames and flashing should make the fault on either of the other phases easier to find.

 

[LarryFine]

They had each wired phase to ground (so A phase to grounding conductor, ect).

Another way of saying the same thing is that the lamps are wired in a wye with the "neutral" grounded.

 

[mivey]

I worked at a steel mill that had an un-grounded delta system and ground lights like that. The lights told us if there was a problem somewhere, we just never knew where and had to run around in golf carts trying to find either a column of smoke or a production manager running around pulling his hair out looking for an electrician.

I left in the late 70s but went back there as a contractor in the 90s and saw that one lamp was out, indicating that it was grounded. The guys there said it had been that way for years, nobody was sure what it meant...

We found one locally after the 2nd fault occured and smoked the transformers. The ground fault indicator had been removed long ago and you could see where it used to be located near the main disconnect.

At some point someone thought they would just remove that silly device on the wall since no one knew what it was for. Expensive mistake. Oil testing would have also shown severe moisture in the transformers that helped them reach their demise during the fault.

A few of many maintenance items that got sidelined over the years. Systemic problem from the top down. Patched and holding for about two years now. The dice are rolling.

 

[Kenshaffer87]

Another way of saying the same thing is that the lamps are wired in a wye with the "neutral" grounded.

Essentially, yes, I was just trying to make it clear that the lamps were not grounded to the grounded phase, but instead to the grounding conductor (equipment ground)