Voltage in Substation Equipment Structures

Could be due to induction and/or electrostatic coupling. I recall having had a similar experience, while I was working in a 400kV Switchyard years back. I was having a very sensitive (Japanese make) line tester with an LED Indication and a beeper. Whenever, I walked inside the 400kV Switchyard, I could sense the line tester in my shirt pocket, blinking & beeping. But, thank God! I never got a shock.

thank you for your insight and of your personal experience relating this. i wanted to know how i can help overcoming this problem?

Freaky.
Has anyone else complained about "shocks"? To be honest I'd look at the resistivity of the earth pit.

yes, the man who was painting the covers of the earth pits complained me he felt slight shocks a reasonable number of time to mention. i immediately motioned him to stop working on it.

Get a hold of a thermal imager and look for hot spots. Sounds like that may tricky due to the high voltages on all of the surrouding objects. This sounds like inductive loading on all surrounding objects, including your salted carbon body. Check all of your existing grounds, then double check the line drawings to make sure all of the design grounds exist. I would then check the original specs for each piece of gear to make sure the intent of the grounding scheme was met.

Find another site which is designed/configured the same as your suspect site. Even if the load values are different, you should be able to scale it to your suspect site.

what has the hot spots has to do with this kind of a phenomenon? i didnt get u. please explain. i have double checked the grounding system and the required grounding scheme was met.

i had the similar idea of checking two or three other sites in the nearby area which have a similar configuration as that of ours but for that i need a special permission which i am afraid i cannot get it as i am a fresh graduate joined as an engineer in this substation. thank you for ur approach.

With the voltage levels you are experiencing, there may be spots of inductive heating associated with the transfer of energy. It's only a possiblity, and may work if there are phase differences associated with a ground issue.

In a substation there are likely to be very high alternating electric and alternating magnetic fields.

While measuring voltage your multimeter is high impedance - 10Megohms+.

At that impedance it does not take much induced current to generate an apparent high voltage.

When you complete a circuit, even at high impedance, your multimeter leads act like an induction loop proportional to the area enclosed for the varying magnetic field, like a winding in a generator ..... and so does everything else in the vicinity, some of the voltage you 'measured was induced in the metal around you, some in the multimeter leads.

As for the gravel - it has a high impedance and so drops more of the induced voltage and the meter reads less, when you are barefoot the the loop impedance drops, therefore more is dropped across the meter which reads a higher value.

Twist the leads together to reduce the enclosed loop and the reading will change.

Try to measure the current and you will find it to be quite small - now the meter is low impedance and the rest of the circuit is high impedance restricting current flow.

i liked your thought process of thinking it the impedance of the multimeter way. but i have checked the readings with different multimeters just to check the functionality of the multimeter. i have tried a wide range from the analog ones to the digital ones which of late have a special feature of EMC criteria.

in that case, even in a very highly inductive area, the meter must be able to give an accurate reading though not precise. even considering the effect of induction, the values may differ by a maximum of 25 to 30 percent. even with that error, still the voltages are considerably high. suggestions are welcome.

The voltage mesurements you have this way is higly dependent on your instruments internal impedance and generally are unreliable. But the fact you're getting a shock is definitely sign of ground fault, no matter how bad design you have there, it shouldn't happen. Also note that grounding deteriorates at long low humidity periods S.M

i am utterly confused at this. we have two contradicting statements here. 1. either the grounding is poor or 2. there may be a ground fault present eternally. how can both lead to the same situation.

The matter is simple; codes bind you to bond all metal structures to Earthing network, if codes have been complied with the painter simply could not get electrical shock while painting the manhole cover.

Codes and standards require that Earthing system in a HV substation is to be designed for safe Touch Potential as well as safe Step Potential, that requirement is beyond the normal practice of earthing and cannot accurately be checked by instruments, all you have to do is to recheck by calculations using formulas for the earthing to be effective.

thank you for your insight...

GA - correct and clear

sorry for my delay in reaching to your active contributions... i did not have internet access... and thank you all for sharing the wonderful experiences and knowledge... i never thought my post would bring such enthusiasm... as you said that i may be experiencing the voltage induced in me which is being reflected in the multimeter, can i expect a change in the result if i check the voltages in an unmanned way i.e., in isolation...

I have been working in energised HV grid statations upto 500 Kv. Practically in a grid conductors are supported on metal gantries with only insulator strings for isolation, all the equipment like CT, PT, CB etc. are supported by post insulators which themselve rest on matal structures and the top of any individual metal support / structure is well above the height of a human being.

http://www.geograph.org.uk/photo/141127

When for a 400 Kv system the codes allow a phase to earth clearance of 354 cm, phase to phase clearance of 400 cm and a creepage distance of 9660 mm in heavily polluted atmosphere there is no element of inductive or capacitive bonding among live parts and a worker standing on the ground.

For earthing design requirements in a grid station please refer to the following link at google.com

http://pecongress.org.pk/images/upload/books/Design%20of%20Earthing%20Final26-31.pdf

Bert has the right answer. As a young EE I was told to park my company car parallel to and under some exposed conductors in a 230kV switchyard. Everybody got a good laugh when I grabbed the door handle and jumped back in response to the jolt I received!

If you work in an environment where step potential exists, you learn very quickly the personal methods you must use to avoid getting a jolt, and how to prevent electrostatic buildup on your person through habits and protective clothing. Properly prepared individuals do not complain, because they aren't trying to kill themselves.

as mentioned by you, one thing in particular coincided with my experience i.e., the voltages near the breaker were higher than those compared to other places... can anyone suggest how i can help improving the current situation in my switchyard.. of course we cannot afford to have a Faraday cage suit for everyone here.... are there any possibilities?

well all the clearances which you have mentioned have been met and i have already cross verified the earthing design considerations.. by all your posts, i, now have a much better view of this phenomenon.. once again thanks to all... if you think so we can proceed this discussion, i would be very much lucky enough and impressed...