Induced current on disconnected power distribution line 1

[veman]

Hi,

We had an incident where a lineman was installing a new line across a road. There are two parallel circuits with one disconnected and grounded at one end. There was a high voltage measured at the other end of the disconnected line.

Does anyone know where I might find information on how to calculate this induced voltage/current based on the proximity of the line to the disconnected line?? We need to change our grounding / work practices to minimize the chance of a bigger problem occurring....

Thank you,
Veman

 

[jghrist]

Electrical Transmission and Distribution Reference Book, Westinghouse Electric Corp., 4th Edition, 1964, has an equation (3) in Chapter 23 that gives the induced voltage on a communication conductor that runs parallel to a power line.

 

[stevenal]

Why calculate? Practice proper equipotential personal protective grounding, and you won't have these incidents.

http://www.hubbellpowersystems.com/powertest/literature_library/pdfs4lib/Chance-Hotline/09-8002.pdf

 

[veman]

Thanks very much for the quick responses. About the equipotential grounding, the wire was coiled at the base of the pole and when our guy grabbed it, it was energized with induction so, because the guy was on the ground, I'm not sure how equipotential grounding could have been applied. The issue is more with our guy not wearing his PPE and the complacency around treating ungrounded wires as live. I was interested in calculating also because we are trying to measure the voltage due to induction and are having a hard time because some of it is DC and some AC and the meter we're using also picks up floating voltages as well...

Thanks again!
Veman

 

[burnt2x]

Hi!
First, maybe you're missing something when you wrote:

"About the equipotential grounding, the wire was coiled at the base of the pole and when our guy grabbed it, it was energized with induction so, because the guy was on the ground, I'm not sure how equipotential grounding could have been applied."

.

Secondly, 1910.269(3) defines the requirement for ensuring an "equi-potential zone" as:

"Equi-potential zone." Temporary protective grounds shall be placed at such locations and arranged in such a manner as to prevent each employee from being exposed to hazardous differences in electrical potential.

Your people don't have to touch the wires, use clamps in doing the chaining to ground.
Third, and most most important; "your people should start grounding at the ground stubs/ terminals, them jumpering the lines to be worked-on.

Feels great to be of help.

 

[waross]

You may want to consider grounding the lines at the point where the work is being done. With long high voltage cables grounded at the supply end and then at the work site, the induced voltages may cause enough current to flow to actually heat the ground rod to the point that the ground dries out and the ground resistance to rise to the point that dangerous touch potentials develop on the ground rod.
A few suggestions that have been used by some utilities:
Drive corner posts and flag off a 20 ft. or 30 ft. square centered on the ground rod.
Connect all safety grounds together.
In severe cases, consider multiple ground rods onterconnected and flagged off.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[veman]

Thank you for the posts. I agree that equipotential grounding is what should have been done. More of a personal interest after the fact thing for me to want to calculate and measure the effects of the induction that occurred.

Veman.