Static Electricity Problem due to high KV overhead cables 2

[Iomcube]

There is a truck loading platform supported by iron columns x4 on each side. The platform will have a FRP roof as well. The whole platform is under high KV cables that are passing above it & we are having static electricity problem at the top section of each column (yellow arrow)

The loading platform will not have any flammable material (HCl & NaOH liquid only).
Any recommendations for mitigation this? If users here require more input from my side please mention.

 

[cranky108]

You can ground them, but that might not help. The issue is the overhead cables can generate a static charge on anything that is not grounded, like a vehicle with rubber tires, or a human with rubber shoes.
Have you tried a grounding clamp for trucks and grounding mats for people.

 

[crshears]

"Grounding mats for people" will only be effective if the person in question is wearing conductive or 'non-dielectric' footwear, in other words WITHOUT the Greek letter Omega on it; I got by for many years of inspections and switching in high voltage switchyards [ including 500 kV ones ] until the company implemented a new policy stipulating that any field staff entering any switchyard were to be wearing dielectric footwear.

I quickly learned to hold my keys in one hand and ground myself against grounded apparatus before, for example, opening mechanism box doors with the other hand [ addition via edit ] ; with this technique any arcing occurred between the key and the apparatus, rather that between my fingertips and the apparatus - and trust me when I say your education in the use of this technique will progress very rapidly, with special reinforcement occurring every time a little blue arc zings your fingertips, followed by a brief presence of "blue air" in the vicinity of your mouth!

 

[cranky108]

I recall growing up and seeing old oil trucks dragging a chain to keep static electricity at bay.

 

[LittleInch]

Isn't this more induced voltage rather than "static" electricity?

Appreciate it does the same thing, i.e. jump across to earth, but there is a very low but continuous current here as well?

As said before - a very comprehensive earthing policy for the structure.
Looks like a very odd place to locate such a structure to me.

Were you falling over when you took this photo?

Here it is rotated a bit.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Iomcube]

LittleInch, I was not falling ...but in a single picture I want to capture everything so I took a panorama photo.

Guys, can you refer to me any standards or book that I can follow for 'comprehensive earthing policy'

Also I want to know the difference b/w 'bonding' & 'earthing'

 

[crshears]

Isn't this more induced voltage rather than "static" electricity?

I would agree it definitely is, but I wasn't about to drag a chemicals guy into the minutiae of electrostatic and/or electromagnetic induction, as I tend to get called a picky bastard whenever I do that ! Thanks for taking that on so I didn't have to.

As to the location, which came first, the tower line or the chemical handling facility?

If a transmission company put up the line over an established handling facility, methinks they would bear some accountability for assisting with the mitigation of the conditions described.

If the handling facility was deliberately built in a HV right-of-way, my first thought would be to wonder why; land for sale on the cheap or something?

The following concerns me, however:

The platform will have a FRP roof as well.

What will be the height of this structure above grade? Has conductor sag been taken into account? You would not want to be in the unenviable position of having put up this structure without the approval of the Authority Having Jurisdiction [ AHJ ]; if the line is ever heavily loaded on a hot summer's day . . .

A sub-contractor once installed lighting standards / pylons in a Toronto Transit Commission parking lot directly under a 230 kV right-of-way without asking the right questions or getting any approvals. The electrical sparks that subsequently flew when the line was heavily loaded on a hot summer's day put on quite a spectacular show; the legal sparks that flew afterward put on a show that was in ways even more spectacular . . .


CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[jghrist]

The "static" voltage problem depends on the line voltage, not the load. The voltage is actually induced in the person touching the not the steel itself, which is connected to earth through the column footings. It may be mitigated by changing the roof from FRP to a steel roof that is connected to the steel columns. The steel roof would shield people from induced voltage.

We investigated a similar problem in a 230 kV switchyard. Workers would get a shock when touching circuit breaker cabinets. The cabinets were properly grounded. We could measure several volts between a piece of metal held up in the air and the breaker cabinet. Putting a piece of steel plate above the cabinet, connected to the cabinet provided enough shielding to reduce the voltage significantly.

 

[stevenal]

What exactly is the problem you are trying to mitigate? Some annoying static-like shocks? If the materials being loaded are not flammable, what is the problem? I've been in high voltage yards where this "problem" is simply accepted as the cost of doing business.

 

[dik]

I've been in numerous high voltage switchyards over the years, and never knew this was a problem... always wearing my Omega boots... if it can cause serious issues (I don't have a pacemaker), it is more than 'a cost of doing business'. If just a little uncomfortable then people should be aware of it to prevent a consequential injury from 'discovering' the problem.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[waross]

I was appointed "Safety Guy" on a capacitor station build.
I received a lot of resource material on grounding and induced voltages.
As jghrist pointed out, the voltage is induced in the person.
There is a voltage gradient through the air from the overhead line to ground.
A person who is not grounded and is between the line and ground becomes a common electrode of two capacitors in series.
The line to the person is one capacitor and the person to ground forms the other capacitor.
If the person touches a grounded object. he will discharge the capacitor formed by his body and ground.
The higher in the air and the closer, on a PU basis, to the high voltage line, the higher will be the voltage of the charge on your body.
The solution is to either stay off the roof, or to make the roof conducive.
If you must touch grounded objects, touch them first with a key or a wrench, and maintain contact until you get a bare hand on the grounded part.

The charge is roughly related to the fraction of the distance to the high voltage line.
If you are 5% of the distance from ground to the line you will have more of a charge than if you are 3% of the distance.
As stevenal said:
"Cost of doing business."
Or;
"If you can't stand the pain, stay off the roof."

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[cranky108]

Actually, it may not be the voltage, but the current in the line creating the larger magnetic field.

 

[waross]

Agreed that the magnetic field will be related to the current.
However, the effect seen here is caused by a division of the voltage transient from the line to the ground plane.
The air forms a very high resistance resistor.
The vertical columns cause very little distortion in the voltage transient.
A person or conductive object on the roof will become a capacitor plate and charge to the voltage at that point in the gradient.
If the person touches a grounded surface, the charge stored on their body will discharge.
The actual charge will be very little but the voltage will be high enough to cause a spark and an uncomfortable shock.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[crshears]

Can't recall if I mentioned this before, but I once went on a night-time 230 kV switchyard walk with a fluorescent tube in my hand; completely dark when held dead flat, slowly increasing to more than full, almost blazing brilliance when fully plumb. QED for electrostatics! And yes, I wore all the appropriate PPE.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]