Grounding hazard from induced currents under open 15kV lines
Grounding hazard from induced currents under open 15kV lines
(OP)
This is a metals plant that transmits 15kV power from a 100MVA, 138kV/15kV Y-Delta transformer across a gravel area about 300 feet ending in another elaborate switching system.
We've got our guys installing some fans on the outside of metal building that's located 30' from the tower. We had them install some bonding straps to the 15kV tower. We are measuring on that ground wire 2 to 3 volts to ground and a whopping 250A. Our people act like this is no big deal and its safe to work on. Can someone explain why this is so?
We've got our guys installing some fans on the outside of metal building that's located 30' from the tower. We had them install some bonding straps to the 15kV tower. We are measuring on that ground wire 2 to 3 volts to ground and a whopping 250A. Our people act like this is no big deal and its safe to work on. Can someone explain why this is so?






RE: Grounding hazard from induced currents under open 15kV lines
RE: Grounding hazard from induced currents under open 15kV lines
It's happening.
RE: Grounding hazard from induced currents under open 15kV lines
I remember a few years ago I was at a plant that had built a large pipeline under those lines. It also carried a current like this. The utility engineer told us that the transmission lines used the earth as a the return path. I just wonder if this has anything to do with it.
RE: Grounding hazard from induced currents under open 15kV lines
We still don't really understand your system so it's hard to say what's going on.
What's in the metal building? You might take a look at it's electrical system and grounding as a starting point.
Alan
"The engineer's first problem in any design situation is to discover what the problem really is." Unk.
RE: Grounding hazard from induced currents under open 15kV lines
So all transmission lines are perfectly balanced 3-phase systems? How is that possible when no load would be perfectlty balanced? I've read one of the definitions of vars as that portion of the generated power not used and returned to the power plant? I truly don't understand...
And those pipelines were literally 1/2 mile from any source of electricity. If you cut into one of them sparks flew. The transmission lines had nothing to do with them either?
RE: Grounding hazard from induced currents under open 15kV lines
RE: Grounding hazard from induced currents under open 15kV lines
Think about a single-phase load connected phase-to-phase. Unbalanced line current, but no resultant earth current.
Yes, my statement is oversimplified. The point I was trying to make is that he should not expect to be seeing a large amount of earth current from a transmission line. Obviously there are earth currents due to line asymmetries, geomagnetic affects, etc. but I would not expect those to be on a scale that would induce 250 amps between a building and adjacent 15 kV power pole. Again I still don't fully understand your situation, but if I were going to troubleshoot this, I would probably start by verifying the electrical system in the building is properly grounded.
You'll have to get someone else to explain your pipeline situation. That's beyond my area of knowledge.
Alan
"The engineer's first problem in any design situation is to discover what the problem really is." Unk.