Induction on Pole from POCO

[Castrovinci]

All,
So I have a rather interesting situation in which I wonder why I got involved, but here it goes.


There is a pole that is owned by the condo association (my customer) that is near 500KV transmission lines. The pole has been there at least 15+ years and is aluminum and houses a plastic globe at the top. I went to change the bulb/ballast as usual business and received a small shock touching the plastic globe. We stopped and reviewed the area thinking maybe the ballast was touching something and was causing it so we shut the whole panel off and tried again to eliminate any near by items. Same issue. We were getting shocked through their gloves. The pole is located a decent distance from where the power lines dip between poles. We had a HV company come out and test the pole and there is 500 volts on the pole, but only at the top. You could touch the bottom of the pole all day and nothing. I have the testing company add a ground rod at the location thinking this may help but the testing company says it won't. Anyone deal with this and have a good solution other than use HV gloves. I have to go back to the association and they are going to want some answers and not the liability of this pole. If I install a fiberglass pole, how can I assure that this won't still be a problem, since right now even touching the plastic has voltage on it. Contacting the power company seems to so far be a pass around the circle and after months of calling. Where to go with this one short of calling police and filling a report of someone getting electrocuted, which will probably get POCO to do something about it.

 

[kwired]

All,
So I have a rather interesting situation in which I wonder why I got involved, but here it goes.


There is a pole that is owned by the condo association (my customer) that is near 500KV transmission lines. The pole has been there at least 15+ years and is aluminum and houses a plastic globe at the top. I went to change the bulb/ballast as usual business and received a small shock touching the plastic globe. We stopped and reviewed the area thinking maybe the ballast was touching something and was causing it so we shut the whole panel off and tried again to eliminate any near by items. Same issue. We were getting shocked through their gloves. The pole is located a decent distance from where the power lines dip between poles. We had a HV company come out and test the pole and there is 500 volts on the pole, but only at the top. You could touch the bottom of the pole all day and nothing. I have the testing company add a ground rod at the location thinking this may help but the testing company says it won't. Anyone deal with this and have a good solution other than use HV gloves. I have to go back to the association and they are going to want some answers and not the liability of this pole. If I install a fiberglass pole, how can I assure that this won't still be a problem, since right now even touching the plastic has voltage on it. Contacting the power company seems to so far be a pass around the circle and after months of calling. Where to go with this one short of calling police and filling a report of someone getting electrocuted, which will probably get POCO to do something about it.

If you call the police and tell them someone was electrocuted they will be expecting to find a dead body.

Can't say I know what is all going on here but you seem to be indicating getting shocked when touching the globe that is made of a insulating material, so that seems to indicate this is more of a static electricity problem then an induction problem. Perhaps you should try some kind of globe with some conductive material in it so it will not hold a charge as easily? Of course that could end up meaning an entire new luminaire but careful selection is necessary to avoid similar issues.

 

[electric_cal]

You say that the testing company read 500 volts at the top of the pole only.
Do you know what type of testing meter was used? Analog or digital?
Also, what is the height of the pole, and how do they know that the addition of a ground rod will not help?

I will be watching this thread with great interest.

 

[big john]

...We had a HV company come out and test the pole and there is 500 volts on the pole, but only at the top. You could touch the bottom of the pole all day and nothing....

If the pole is conductive you will not have a 500V difference of potential between the top and bottom of the pole. I don't know what they measured, but it wasn't the pole itself.

...Anyone deal with this and have a good solution other than use HV gloves....

Yes, bonding is the key. You put yourself and the equipment you're working on at the same ground potential. Conductive components should already have equipment grounds performing this function. Keep small bonding straps with you to temporarily connect to components you have to isolate, like ballast wiring.

...Since right now even touching the plastic has voltage on it....

I'll never say something is impossible, but I've done a lot of work in high voltage substations and never seen anything like that. Try taking some voltage readings to determine what's going on, you may need something like a Simpson, as induction tends to upset DMMs.

 

[Castrovinci]

Reply

Reply

If you call the police and tell them someone was electrocuted they will be expecting to find a dead body.


Can't say I know what is all going on here but you seem to be indicating getting shocked when touching the globe that is made of a insulating material, so that seems to indicate this is more of a static electricity problem then an induction problem. Perhaps you should try some kind of globe with some conductive material in it so it will not hold a charge as easily? Of course that could end up meaning an entire new luminaire but careful selection is necessary to avoid similar issues.

LOL No the police would take a report of a shock and then it would go to POCO's radar, but that was a joke.


I don't think is a static thing, but more so a constant voltage induced from the air. It's going to be hard to get the association buy in when I can't promise them getting a new fixture or pole will fix it.

 

[meternerd]

[I don't think is a static thing, but more so a constant voltage induced from the air. It's going to be hard to get the association buy in when I can't promise them getting a new fixture or pole will fix it.]

It Won't...... Based on my experience only.....yes, you can and usually will be shocked when in proximity of transmission voltages. When working close to those lines, "bonding on" is a common practice. What that means is that you "bond" yourself to whatever you are working on to keep you and it at the same potential. Just hanging on with one hand and working with the other is usually good enough. If you need both hands, a small conductive jumper from your body to the structure will work. What's really happening is that your body is charged up to a potential different than the thing you're touching and the shock comes when you equalize voltage differences. Induction is a magnetic effect, What you're seeing is a static effect. The plastic will store a static charge until you touch it and it discharges through you. I know it sounds crazy to intentionally touch something that's shocking you, but there is negligible current when you have equalized the potential of your body and the structure you're working on. The condition is worse on windy days. I'm sure I'll get flak for this post, but that's my experience. Do what you feel is necessary to keep safe.

 

[GoldDigger]

The only way you could have a substantial difference in voltage between two ends of a conductive pole would be as a result of magnetic induction.
And if that were the case it would be very difficult to measure that voltage since the same induced voltage would appear on the meter leads.
Something is not what it seems to be.

 

[Castrovinci]

hmm

hmm

If the pole is conductive you will not have a 500V difference of potential between the top and bottom of the pole. I don't know what they measured, but it wasn't the pole itself. Yes, bonding is the key. You put yourself and the equipment you're working on at the same ground potential. Conductive components should already have equipment grounds performing this function. Keep small bonding straps with you to temporarily connect to components you have to isolate, like ballast wiring. I'll never say something is impossible, but I've done a lot of work in high voltage substations and never seen anything like that. Try taking some voltage readings to determine what's going on, you may need something like a Simpson, as induction tends to upset DMMs.

I didn't see what type of meter or how they did the test but I think it was measured by some special meter that measures by the field around it. Not an expert on high voltage hence why we called them in so I could say for sure. sorry

The Ground rod did nothing. They added one this morning

Not sure what the extra voltage readings will do since we know its from the transmission lines already as all power/wire to this pole has been removed for testing. The association is looking for a permenant fix. It's great I know to put gloves on and bond my equipment etc, but they are worried about the average Joe servicing this or an issue later where it gets worse.....down the whole pole.

I suppose I can go back and tell them to move the location but there gonna ask me why this has recently become and issue so I want to see if there is a better option.

 

[Castrovinci]

reply

reply

Based on my experience only.....yes, you can and usually will be shocked when in proximity of transmission voltages. When working close to those lines, "bonding on" is a common practice. What that means is that you "bond" yourself to whatever you are working on to keep you and it at the same potential. Just hanging on with one hand and working with the other is usually good enough. If you need both hands, a small conductive jumper from your body to the structure will work. What's really happening is that your body is charged up to a potential different than the thing you're touching and the shock comes when you equalize voltage differences. Induction is a magnetic effect, What you're seeing is a static effect. The plastic will store a static charge until you touch it and it discharges through you. I know it sounds crazy to intentionally touch something that's shocking you, but there is negligible current when you have equalized the potential of your body and the structure you're working on. The condition is worse on windy days. I'm sure I'll get flak for this post, but that's my experience. Do what you feel is necessary to keep safe.

I think they measured 500 voltages in a field around it since it is plastic globe I don't think there is any full way to get 100 percent reading....I don't know.........


This may work normally except you can't even touch the pole for a second. If you put gloves on and touch an insulated tool to it it blows a hole through the rubber. One would say that's ways more then 500V, but this is what they measured from there meter. Now maybe this was on the plastic and the pole had more, don't know. It is continuous too not just a one time static charge like rubbing you socks on carpet and touching a door handle......Its continuous.

 

[big john]

...Not sure what the extra voltage readings will do since we know its from the transmission lines already...

But we don't know what parts have voltage on them relative to what other parts, and that's the problem you're trying to fix.

Bonding those parts may be the easiest, cheapest solution if you get an idea of what parts are energized.

 

[GoldDigger]

But we don't know what parts have voltage on them relative to what other parts, and that's the problem you're trying to fix.

Bonding those parts may be the easiest, cheapest solution if you get an idea of what parts are energized.

But if there is a voltage relative to remote earth ground, then a worker on an earthed boom, lift or ladder will be exposed to the high voltage unless he also becomes part of the equipotential bonding at the top of the pole.

 

[meternerd]

[This may work normally except you can't even touch the pole for a second. If you put gloves on and touch an insulated tool to it it blows a hole through the rubber. One would say that's ways more then 500V, but this is what they measured from there meter. Now maybe this was on the plastic and the pole had more, don't know. It is continuous too not just a one time static charge like rubbing you socks on carpet and touching a door handle......Its continuous.]

The reason it's continuous static is because the charge reverses polarity every cycle, but if you could take away the voltage source instantly, the charge would remain on the plastic for a while.

I know it sounds nuts...when working live transmission lines from helicopters, bonding on is an absolute necessity and there is no ground. You're flying. But your body and the copter are at a different potential than the wire, so until you equalize, you'll get shocked (or killed). It draws a pretty hairy arc when you first bond, but there is no option. Same deal you're talking about but on a smaller scale. Bonding will only work when you and everything around you are at the same potential. If all around you is grounded but you are not, you'll rise to a potential different than ground because you're insulated. But...you'll still have an issue with the plastic because it won't discharge like a metal structure. Two different problems. Static and induction. Same as EPG "equipotential grounding" when working on de-energized distribution lines. If the line does accidentally come hot, you are NOT in parallel with the line to ground circuit, so you remain protected. The current flows around you.

If you put a jumper from the pole to a good solid remote ground and you see much current flow at all, you may have other problems, but unlikely they could produce 500V. Using a low impedance meter or a Wiggy would probably show a much lower voltage.

The only solution I can think of is to install a "ground grid" using metal grating around the base of the pole that is bonded to the pole. Then any current will flow around you and to the ground. But even then, if you insulate yourself from the grid, you'll build up a charge and get zapped when you touch it again. Frustrating stuff. Lots of time and money spent minimizing the effect, but it never really goes away. Good luck.

 

[big john]

But if there is a voltage relative to remote earth ground, then a worker on an earthed boom, lift or ladder will be exposed to the high voltage unless he also becomes part of the equipotential bonding at the top of the pole.

Agreed. That's why I mentioned temporary bonds before, because I don't think there's any way around that: They could install completely non-metallic pole standards, and I bet a worker could still get a bite off of disconnected ballast wiring. So if they're worrying about maintenance risks, a fiberglass pole wouldn't solve the problem.

But if they are developing voltages between separate components of the fixture then bonding would address those and help reduce the number of hazards.

 

[GoldDigger]

Just thought of an interesting whacky possibility:
The entire pole is energized to 500V because of really high undesireable earth currents at the base. A person standing at the bottom of the pole would not get a shock since the would be at the potential of the surrounding earth.
But at the top of the pole the person would be capacitively coupled to remote earth (the planet) and see a voltage difference between them and the top of the pole.
Second thought:
If whatever is inducing the voltage can source a lot of current then, as we know, just adding a high resistance ground electrode at the base will not change the potential much.

Quick test to make: Run a copper wire from top to bottom of pole and measure voltage while open circuited at the bottom and measure current when short circuited to the base of the pole. {Possibly there is a joint in the pole or some other break in the current path.

 

[meternerd]

I just had a thought...is the transmission 3 wire AC or 2 wire DC? If it's 2 wire there won't be any induction. But....DC transmission (usually 500KV or 1MV) is referenced to ground so that if one leg opens, the other leg will still supply current, but the return current will be through the earth. It's been known to kill cattle when it happens. Relays are installed to alert the POCO when it happens. Also, I've been told that a lot of transmission is 3 wire grounded Wye, but the neutral in not run with the phases. If that's the case, a high impedance ground fault could cause the fault current to flow though the earth back to the substation. Should be relays to alarm it, though. I've seen it happen on 7200/12,470 distribution when a primary neutral opens up and current flows through the earth until it finds another pole ground connected to the neutral. Customers complained of shocks in the shower that were not eliminated when we opened the main breaker or even when we lifted the transformer secondary leads. Weird stuff.... but maybe you're seeing distribution problems that have nothing to do with the transmission. Are there any other metal structures nearby that are also shocking you?

 

[kwired]

The OP said he is getting shocked when touching the non conductive globe - about has to be a static voltage to be able to do that.

 

[GoldDigger]

The OP said he is getting shocked when touching the non conductive globe - about has to be a static voltage to be able to do that.

If the globe is really non-conductive, then it pretty much would have to be static.
But if you get more than one shock with repeated touches, that rules out static.
Some plastics are conductive enough to deliver a shock.
In the vicinity of really high tension lines there can be coronal discharge, but again I would not see this as a simple explanation.
There are ground clearance requirements for high tension lines. Does that include limits on poles are structures under the footprint of the lines?

 

[meternerd]

I think we need more info. Was the 500V AC? Was it a high impedance meter? Bonding it to what? Remote ground or bottom of the pole. Still sounds like something more than proximity to the 500KV lines. I've worked around 345KV and 230KV in VERY close proximity with no effects. The only time I got zapped was working in a 115KV substation on a military base in Alaska. With that one, you could write your name in the metal using the arc from the induction. Measured 130 volts to ground. But that was just 20 or 30 ft from the HV. But "bonding on" stopped it. Inside the sub here in Truckee, the lineman hooking up video cameras was getting zapped while up in an insulated bucket truck. Read 120V on the ground from the truck to the station ground grid. But again, close to HV. I'll be following this one to see what everyone comes up with. But like the old saying goes..."If you let go before it gets to your elbow, it won't kill ya". As far as clearances, I'm sure there must be, but in reality, it's a crap shoot. In Alaska, the 345 lines sagged due to snow load and the snow below was so deep that there was only 10 ft from the lines to the snow. Cross country skiers said they felt a "buzzing" while they were crossing under. DUH! Stay away!

 

[K8MHZ]

It sounds like the pole is acting like an antenna.

The end of a vertical antenna can have a voltage differential of hundreds of volts to ground, where the feed point will be at or very near 0.

The odd part is why. Not only that, on an antenna, the ends have high voltage and low current, but the feed point has high current and low voltage.

Also, this happens at RF frequencies. I have never heard of it at 60 Hz.

Still, it does happen all the time with radios.

 

[busman]

My guess is that the measurement was a field strength measurement and the units probably should have been 500 V/m.

That would seem to make more sense.

Mark