60V potential "tingling"sensation" in Switchyard

[NAZ55]

I tried this question under another subject line and received very few responses so here we go again. We have a situation where personnel are experiencing tingling sensation while touching equipment grounded to the 345kV switchyard grid. The voltage potential that exists is about 60V from the surface rock to the grounded strucutres. Any idea what could cause that? I have calculated the open circuit potentail which exists underneath the centerphase bus at the surface rock level to be 12kV and am wondering if there's a way to correlate that to the 60V potential difference that the personnel are experiencing. The bus is 19 ft high from the surface rock.

 

[stevenal]

17 responses is few?
thread238-257669
Capacitive coupling is still the answer.

 

[racobb]

Agree with Stevenal, seemed like you got your responses. Anyway you say voltage to grounded structures. Are you sure that they are grounded? And if so how do you know, just because they are supposed to be?

Have you checked? What is the type of soil? What is the impedance of your ground grid?

Do you get it from all structures or just one or a few? Maybe they did not get tied down. If it is just one, put on some gloves and tie it down and see if it solves the problem.

I have seen instances where wells with electrodes had to be installed in sandy soil conditions to lower the Z of the grid.

Alan

 

[xxjohnh]

In substations there is a lot of different parts of galvanised steel bolted together with one part of it grounded. The bolted connections may not be good conductors. This is seldom checked on installation.

 

[PQ101]

To zazm:

I investigate power quality cases for electric utility in mid-west, and resolved many different cases (RFI, stray voltage, or power line issues). My favorite line-always start from the ground up.

Based on information provided (more needed) it is believed that the tingle is due to leakage to ground somewhere, or possibley due to improper (rusty, or less than adequate ground-bonding connection), Check for grounding of substation/switchyard structure, parameter fence, and check inside of relay house to verify if you have the same issue there as well. Check all your 120v outlets inside the sub, check the stepdown xfmrs that supply voltage (tied to 12KV bus for 208Y/120v control power).

On your 12KV distribution if youhave a milligause meter go ahead and check for the highest magnitude. Do you have RFI locator Model 240 from Radar Engineers?

Attach as many pictures from different areas inside the sub, tell me where you take highest-lowest readgs, and provide as muchh information as possible i.e. when did it start, does it fluctuate depending on loading AM/PM, etc.

You will find the source of stray voltage.


Providing power quality solutions that empowers you!!!

 

[jghrist]

I think the best explanation is in the original thread. This is that the voltage is being induced in the person, not in equipment. The voltage has very little energy associated with it, so the small "tingle" when it is discharged by touching grounded equipment is harmless. Wearing insulated boots and standing on insulating crushed rock ground cover keeps the voltage from draining to ground.

Modeling the induced voltage in an irregular object like a person would be very difficult. Measuring the voltages in a live substation and experimenting with different resistances to ground could shed some light on the problem.

 

[PQ101]

To jghrist:

Strongly disagree with 1st paragraph "the voltage has very little energy associated with it.....". The potential, 60 volts can kill a person if/when condition is right as we say in power quality. This is a "stray voltage case" and ZAZM is looking for help-solution.

As you inspect the sub everything that you see around you is a suspect, till you eliminate them one item at a time. I'd say you should start (taking the voltage reading) from outside the fence-coming in. Then check all 4 corners.

I basically work in switchyard/substations taking care of maintenance,etc. and see all type of problems everyday. Good data collection and investigative work will lead you to solve the problem. Outside of parameter fence, inspect for damaged pole grounds (i.e. on 34.5KV and 12.47KV underbuilt, if you have a broken-damaged pole ground on 12KV distribution system, etc.). If there are pole-mounted transformer stations or lighting fixture inside the sub, check for improper neutral-ground bonding connection. Any broken ground could cause stray voltage.

Utilizing a basic digital voltmeter set one probe on metallic object i.e. light fixture, etc. and other probe to the earth ground.

Power quality solutions that empowers you!!!

-----------------------

http://WWW.POWERCHX.COM

 

[stevenal]

Ah yes the modern high impedance digital voltmeter; guaranteed to pick up potentials where there is no energy behind them. I'm surprised only 60V was measured. Like a static shock, 1000s of volts are involved until the charge is drained. If this is a safety issue, we better shut down the grid.

 

[PQ101]

To Stevenal:

I would'nt recommend that, just solve the stray voltage issue and move on. These are common issues on electrical systems, you just have to spend time and resolve it.

Power quality solutions that empower you!!!

-----------------------

http://WWW.POWERCHX.COM

 

[stevenal]

To PQ101,

You are right this is a common issue. Happens in all high voltage switchyards that have good rock on a dry day. No moving on for those who believe this is a problem, they can spend their entire careers here.

 

[racobb]

Amen

Alan

 

[PQ101]

Stevenal:

I was looking at my crystal ball when I said that. Of course you have to know what you are looking for, and eliminate non-related issues. You will identify the source.

Good Luck with your investigation.

Power quality solutions that empower you!!!

-----------------------

http://WWW.POWERCHX.COM

 

[PQ101]

To ZAZM:

If you are close to Chicago-Gary, Indiana area, I can swing by for a cup of coffee and help idetify the problem-cause.

On utility side (transmission, sub-transmission, and distribution systems) or on facility-plant side, no matter how complicated the case is, it will get resolved within days if not hours. All you need is good data collection, and patience.

Power quality solutions that empower you!!!

-----------------------

http://WWW.POWERCHX.COM