"Stray Current"-40 amps

[kwired]

While I wasn't thinking of the ground being paralleled with the neutral as to be causing the current in the ground, simply because there is no load on the neutral to produce any current, but what about if at the transformer the neutral is connected to the XO, and the grounding conductor is connected to the transformer frame, which would also be connected to primary XO? and on to the MGN?

What if they are? They are still connected together although not directly, to create a parallel path. Now have a transformer with feed through primary conductors that go on to some other load(s) that uses the neutral, and throw in a poor connection someplace between where the two conductors in question are connected and now you have an alternate path of less impedance current is going to flow there, some will flow there if all connections are good but will be very small amount.

An inductive loop from not having all phase and neutral conductors in same raceway is also a possibility.

We need to ask OP if this objectionable current is still there if the main is open at the facility, that would indicate that it likely is coming from someplace outside the facility.

 

[ghostbuster]

We need to ask OP if this objectionable current is still there if the main is open at the facility, that would indicate that it likely is coming from someplace outside the facility.

This is a critical care facility.Special arrangements would have to be made to turn off all the power.However,I will be arranging a 20-30% shedding of load(turn off main A/C s etc. for 5- 10 minutes).If this is an induced current flow, there should be a corresponding reduction in this loop neutral/ground current flow.

 

[dbuckley]

Tell you what - I'd be very leery of opening that 40A ground loop, even though doing so may be diagnostically useful, based on the one in a thousand chance it is the primary neutral return for the rest of the street. That could really hurt.

40A ground loop unexplained bad, fried electrician worse.

 

[hardworkingstiff]

It's puzzling that there is no current on the GEC. This really makes me curious as to how the neutral and ground are connected at the source. Is it known that this circuit goes directly to the transformer?

 

[hurk27]

Tell you what - I'd be very leery of opening that 40A ground loop, even though doing so may be diagnostically useful, based on the one in a thousand chance it is the primary neutral return for the rest of the street. That could really hurt.

40A ground loop unexplained bad, fried electrician worse.

While I would not expect this neutral to grounding conductor to be a primary connection, in any way, as I said before the current is just too high for being primary current even if it was the current of an ungrounded conductor, which at 160 amps on the secondary, will be only 4 amps primary @ 19.2kkv, even at a 14.4kv primary were only talking 5 amps and 4150v is still only 18 amps so to be 40 amps maybe a XO to XO bucking balance problem like when you feed a Y source to a Y primary and the secondary is out of balance, but the OP says he has a perfect 160amp on all three phase, so that should rule that out, so my only thing I could think of is another service where there is a lost secondary pulling secondary neutral return through this grounding conductor back the MGN through the transformer neutral???? just don't know without knowing how this grounding conductor is connected?
Around here a pad mount transformer is fed with 3 separate XLPs with each having its own concentric neutral, I could not see loosing all 3 concentric neutrals, maybe they didn't land then all in the ground lug? and some go to the XO lug, which would mean that if the ground lug connection is bad it would explain the path for current to the rest of the transformers down the road if the MGN at the pole is also bad? but that would mean, too many mistakes to make that happen

But I do agree with that I would not open this grounding to neutral connection until I know what the current is coming from and that it can be removed before this connection is opened.

 

[dbuckley]

I dont understand the exact arrnagment from the detail yet either, but my thought about the 40A is that there is a small possibility that this current is originating from other transformers "further down" the supply route returning back to the substation through this instalation.

 

[mxslick]

Answers to Questions:

HWS:
5 separate underground PVC ducts (all filled with water)

3 for parallels ABC
1 for parallel neutral
1 for bare grounded conductor

DR:
It is a dedicated padmount tx. for this facility

Hurk:
no current flow on main water pipe or gas line

KW:

Ground Current was measured and then used summing network to determine current direction flow.It is all 100% flowing into and then out of this facility at this main switchboard as per dwg..

It would appear there are 3 H.V. switches in 1 padmount cubicle outside this facility(approx. 50' from this facility padmont tx)..One of these switches then feeds the stepdown dedicated padmount tx. feeding this facility.The other 2 appear to feed the rest of this subdivision (houses,street lights etc.).

Hmmm, a critical clue surfaces....

may want to be careful not to break the connection at your facilities service - you may possibly be opening the POCO primary neutral that is not connected correctly in the POCO equipment.

Tell you what - I'd be very leery of opening that 40A ground loop, even though doing so may be diagnostically useful, based on the one in a thousand chance it is the primary neutral return for the rest of the street. That could really hurt.

40A ground loop unexplained bad, fried electrician worse.

Deja vu, I think someone said something about that a while back:

Willing to bet the primary and secondary neutral bond is lost somewhere nearby. (If primary is wye that is.)

I dont understand the exact arrnagment from the detail yet either, but my thought about the 40A is that there is a small possibility that this current is originating from other transformers "further down" the supply route returning back to the substation through this instalation.

You got it right, see the critical clue highlighted above.

ghostbuster, get the POCO out there ASAP to investigate a possible lost primary neutral.

 

[ghostbuster]

UPDATE:

Utility just left this site:

1.They measured the same 40 amps on this same bare wire ground inside their padmount Tx.It was connected to the starpoint on the secondary side.

2.The transformer high side it was revealed is delta.(no H.V. neutral to worry about).

3.The utility simply disconnected this bare wire ground and left the site.

 

[LarryFine]

The utility simply disconnected this bare wire ground and left the site.

Well, that'll get rid of the current on that wire.

 

[Smart $]

UPDATE:

Utility just left this site:

1.They measured the same 40 amps on this same bare wire ground inside their padmount Tx.It was connected to the starpoint on the secondary side.

2.The transformer high side it was revealed is delta.(no H.V. neutral to worry about).

3.The utility simply disconnected this bare wire ground and left the site.

If the 40A current is no longer on the neutral and bare ground at the switchgear, the disconnecting of the bare ground at the xfmr would verify it was induced circulating current from conductors not in close proximity.

 

[ghostbuster]

If the 40A current is no longer on the neutral and bare ground at the switchgear, the disconnecting of the bare ground at the xfmr would verify it was induced circulating current from conductors not in close proximity.

Yes,the "new" measured neutral current dropped to 0 amps with this bare wire ground disconnected.

 

[Smart $]

Well, that'll get rid of the current on that wire.

But it only eliminated one path... as the bare ground wire is connected to the neutral and GES at the other end too.

Being bare, it cannot be assumed to be the only path... until verified.

Perhaps the POCO disconnected the bare ground and the 40A current on both it and the neutral disappeared.

 

[hurk27]

I would check to see what if any voltage you have between the transformer case and earth, also check for voltage between the neutral and earth, if there is voltage then you still got a very dangerous problem, to have current on the grounding would mean you would have a voltage differential between the two conductors, if this is true then I would suspect you now have voltage on the neutral or transformer case.

 

[kwired]

UPDATE:

Utility just left this site:

1.They measured the same 40 amps on this same bare wire ground inside their padmount Tx.It was connected to the starpoint on the secondary side.

2.The transformer high side it was revealed is delta.(no H.V. neutral to worry about).

3.The utility simply disconnected this bare wire ground and left the site.

1 did they check the connection for proper use of terminals and proper tightening?

2 just because that particular transformer does not use a primary neutral as part of the current carrying circuit does not mean the neutral feeding it does not carry neutral current from somewhere else down the line.

3 I would have wanted to know a little more about where the source of the current may have been coming from before opening the loop - there could have easily been 7200 or more volts potential between ends of whatever got opened. It likely was just a loop created by induction - I have stated earlier that the bare ground running back to the same point as the neutral was not needed and can easily cause problems like this.

This is a critical care facility.Special arrangements would have to be made to turn off all the power.However,I will be arranging a 20-30% shedding of load(turn off main A/C s etc. for 5- 10 minutes).If this is an induced current flow, there should be a corresponding reduction in this loop neutral/ground current flow.

Sounds like a good time to see if the emergency generator works to check out the problem so that you or a lineman doesn't need to be a patient.

 

[ghostbuster]

1 did they check the connection for proper use of terminals and proper tightening?

2 just because that particular transformer does not use a primary neutral as part of the current carrying circuit does not mean the neutral feeding it does not carry neutral current from somewhere else down the line.

3 I would have wanted to know a little more about where the source of the current may have been coming from before opening the loop - there could have easily been 7200 or more volts potential between ends of whatever got opened. It likely was just a loop created by induction - I have stated earlier that the bare ground running back to the same point as the neutral was not needed and can easily cause problems like this.
.

KW.

I appreciate your feedback,but I had little control over this situation.

The utility showed up at this remote site with no advance warning.I did not have a chance to discuss or have them check any of the above items .

If this line crew had any concerns with this installation, before disconnecting this ground wiring,they had the opportunity to discuss with their own utility engineers.They chose not to.I got a follow-up call from their head office saying basically they have resolved all these site problems to their satisfaction-End of Story

 

[petersonra]

I am not real conversant with this kind of situation but I seem to recall that it is common to install a piece of plastic conduit in the metal service conductor conduit to eliminate this kind of problem. Isn't breaking the ground wire about the same thing?

 

[winnie]

If you want to keep diagnosing this after the fact, as a test you might run a closed loop of wire 'around' the duct bank, simply laying on the ground between transformer and building, with one 'side' roughly above the duct that had the neutral, and one 'side' above the ground. If you can measure significant current flow in this otherwise unconnected loop, then you will have pretty much confirmed the induction scenario.

-Jon

 

[ghostbuster]

"quick experimental results"

100 amps on wire

8 amps induced on bare wire ground loop

refer to picture

 

[xformer]

Willing to bet the primary and secondary neutral bond is lost somewhere nearby. (If primary is wye that is.)

That is what my thought is on the matter.......

 

[LarryFine]

refer to picture

An air-core 1:1 transformer. What's the open-circuit secondary voltage?