Static Discharge on pole lights at Nat. Gas Power Plant

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Switcher

Member
Hello all,
We recently we contracted to replace bulbs and ballast in metal halide pole lights at a peak power natural gas power plant. Some of these fixtures are about 20 ft from a 500,000 volt primary line. These fixtures are discharging static electricity when our tech changed the bulb thru gloves rated for 17500 volts. Our tech stated that if he put a pair of pliers near the light it would arc a large static dischard countinuosly and increasing in intensity as he got the pliers closer to the light. These poles have ground rods installed at the base of them and the bottom of the pole is bonded. Our Tech also tried installing a temporay #10 ground wire directly from the ground rod to the light but when he got the wire close to the light fixture it shocked him enough that he gave up on that idea. As he moved his hand (with gloves on) close to the light he could feel a vibration and as he was about to touch the light its shocked him. After he made contact with the light it no longer shocked him. Any Ideas on how we might resolve this issue where these fixtures can be maintained safely?

Thanks in advance,
Alan Helton
 
walton

walton

Member
Location
Sacramento, CA
Sounds like you're dealing with touch/step potential. Is the tech on a ladder or boom truck that's base is some distance from the pole? When he touches the pole he is receiving a static charge as he is brought up to the same potential as the pole. You need to establish an equipotential plane around the tech. The yard you are describing should have a ground grid to help prevent this type of thing. You should talk to the Utility Company about an usafe condition. Be careful.
 
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Switcher

Member
We are using a boom truck that is about 10 ft from the pole when we lift up. How do i establish an equipotential plane? Is this a dangurous situation or something harmless out a weird science episode?
 
walton

walton

Member
Location
Sacramento, CA
Just a guess but I think you are dealing with a capacitive charge in the pole caused by the EMF of the 500KV lines. I would be careful and let the Utility Company know what is happening. One option might be to attach a cable to your truck that is connected to the ground rod and light pole making the truck equal in potential to the pole. This would bring your work platform up to the same potential as the pole and should prevent the arcing. Again be careful. We deal with this at our 69kv switch yard by encircling the entire yard with 4/0cu and a 4/0cu ground grid (20' x40') covering the entire yard. All metal is bonded to the grid so everthing is at equipotential.
 
C

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
I've had this happen to me also. I was changing lamps/ballasts on 50' poles next to a transmission line, I'm not sure of the voltage but it was about 20 feet away. I boomed up and got a pretty good tingle as soon as I touched the reflector. The circuit was off too. I took out my glow stick and it glowed anywhere near the head. Put it in my backpocket(it was still on) and touched the fixture again(barehanded) and the glow stick went off still in my pocket. I looped a #4 bare from the boom to the pole but it still buzzed me anytime I touched the fixture. Weird. Hopefully it'll be awhile before those lights need servicing again.
 
ELA

ELA

Senior Member
Occupation
Electrical Test Engineer
That is both interesting a little scary. I am surprised you have not gotten a response from a person here who works around distribution lines.

I am a little hesitant to comment since I am no expert in this area.
When the tech ran a ground wire from the rod directly to the light I am guessing you meant near the top of the pole?

It would have been nice to have a reading of the current that flowed in that wire to help you decide just how dangerous this might be.
 
H

hurk27

Senior Member
Location
Portage, Indiana NEC: 2008
you need a bond on suit, it's a conductive suit that has a bond on wire and clamp to attach to the fixture, this brings your body to the same potential as the fixture, the problem is not the fixture grounding, but the fact that you are isolated from ground and in the close proximity to the 500kv lines you will build up a static charge that needs to be drained, in some cases just a static wrist strap will keep the charge from building up, but can be un comfortable with the vibrations you feel.

Edited to add that also you should bond the truck to the ground rod to prevent it from building up a static charge.

You might be able to borrow a bonding suit from the POCO, most high line workers should have them
 
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Pierre C Belarge

Pierre C Belarge

Senior Member
Location
Westchester County, New York
walton said:
Just a guess but I think you are dealing with a capacitive charge in the pole caused by the EMF of the 500KV lines. I would be careful and let the Utility Company know what is happening. One option might be to attach a cable to your truck that is connected to the ground rod and light pole making the truck equal in potential to the pole. This would bring your work platform up to the same potential as the pole and should prevent the arcing. Again be careful. We deal with this at our 69kv switch yard by encircling the entire yard with 4/0cu and a 4/0cu ground grid (20' x40') covering the entire yard. All metal is bonded to the grid so everthing is at equipotential.
Click to expand...

hurk27 said:
you need a bond on suit, it's a conductive suit that has a bond on wire and clamp to attach to the fixture, this brings your body to the same potential as the fixture, the problem is not the fixture grounding, but the fact that you are isolated from ground and in the close proximity to the 500kv lines you will build up a static charge that needs to be drained, in some cases just a static wrist strap will keep the charge from building up, but can be un comfortable with the vibrations you feel.

Edited to add that also you should bond the truck to the ground rod to prevent it from building up a static charge.

You might be able to borrow a bonding suit from the POCO, most high line workers should have them
Click to expand...


I would lean towards what is posted in these two posts.
I would still contact the Utility company.

And a Faraday cage/suit is pretty cool...if you do get to use one, it is now absolutely mandatory to have pictures taken. ;)
 
H

hurk27

Senior Member
Location
Portage, Indiana NEC: 2008
I still question the safety of working 20' from 500kv lines, a tool pointed in the wrong direction might cause a flash over? not sure on that one, maybe Charlie could chime in on the safe working distance.
The ones I work around here are at least 100 to 200 feet in the air on towers, that fly overhead. even then they will build up enough static voltage on your body to give you a good jolt when you touch something metal, worse if that metal is bonded to earth.
 
ELA

ELA

Senior Member
Occupation
Electrical Test Engineer
Switcher said:
Hello all,
These fixtures are discharging static electricity when our tech changed the bulb thru gloves rated for 17500 volts. Our tech stated that if he put a pair of pliers near the light it would arc a large static dischard countinuosly and increasing in intensity as he got the pliers closer to the light.
Click to expand...

hurk27; said:
you will build up a static charge that needs to be drained, in some cases just a static wrist strap will keep the charge from building up, but can be un comfortable with the vibrations you feel.
Click to expand...

Would this be defined as "static electricity?" or that your body experiences induced currents from being in the electric field gradient of the transmission lines?

To my understanding static electricity is generated by "the heat of friction" of two insulators in motion against each other.

If the arc is continous that implies a continuous source, not a static one.
 
don_resqcapt19

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
hurk27 said:
I still question the safety of working 20' from 500kv lines, a tool pointed in the wrong direction might cause a flash over? not sure on that one, maybe Charlie could chime in on the safe working distance.
The ones I work around here are at least 100 to 200 feet in the air on towers, that fly overhead. even then they will build up enough static voltage on your body to give you a good jolt when you touch something metal, worse if that metal is bonded to earth.
Click to expand...
The minimum approach distance from a 500 kV line is 20' per OSHA. That would be the closest point of the person or his tools or equipment.
 
H

hurk27

Senior Member
Location
Portage, Indiana NEC: 2008
ELA said:
Would this be defined as "static electricity?" or that your body experiences induced currents from being in the electric field gradient of the transmission lines?

To my understanding static electricity is generated by "the heat of friction" of two insulators in motion against each other.

If the arc is continous that implies a continuous source, not a static one.
Click to expand...


Good question. I know it behaves like a static charge because if you touch a grounded metal object often enough it wont build back up fast enough to shock you. this is why a wrist strap works. (at least at 100' or more from the lines)
 
S

Switcher

Member
Thanks for all the input guys. I discussed this issue with the plant manager and we have decided to wait until the fall to repair the 2 fixtures that are affected. They will be bringing the plant down for some other planned maintenance.
 
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