Step potential????

[Dickieboy]

First off give me a laymens definition of Step Potential.


When grounding inplant industrial substations,when does step potential come in to play and how do you combat it? ie: How do you calculate the fault current and how do you design a safe system????


dick

 

[jim dungar]

First off give me a laymens definition of Step Potential.


When grounding inplant industrial substations,when does step potential come in to play and how do you combat it? ie: How do you calculate the fault current and how do you design a safe system????


dick

What type of substation is this an open air outdoor or an indoor unit style?

 

[dereckbc]

Step Potential: The voltage between the feet of a person standing near a high voltage electrical fault to earth.

Mainly associated in high voltage sub-stations when something like a 69 KV or higher feeder faults to earth/ground and the current dissipates from the point of the fault. It is the voltage developed from the I*R properties of the dirt so the distance between your feet can develop deadly voltages.

In sub-stations they use a ground grid constructed of 250 MCM cable or larger on 20 foot centers and ground rods at each intersections laying just beneath the crushed stone. Then all structures are bonded to the grid, and areas where workers are likely to be working will have steel plates to stand on that are bonded to the grid. Everything is cad-welded together. The grid and all the bonded components form what is known an equipotential ground plane.

 

[Dickieboy]

Jim these are typically indoor for 13.8, 4.16 and .48KV lineups with outdoor transformers.

dick

 

[Dickieboy]

Thanks derek,,,,,,,,do you have a link to any documentation? I have been unable to find any.
dick

 

[iwire]

Step potential is an issue at all voltages as far as I know, just ask a dairy cow. :smile:

Girl Killed at Metal Light Pole

Ground Rod at Outside Generator

 

[mivey]

Refer to IEEE Std 80.

You might also want to read this for some RUS substation info:
http://www.usda.gov/rus/electric/pubs/1724e300/1724e300.pdf

Note the difference in step voltage and touch voltage

 

[iwire]

Note the difference in step voltage and touch voltage

I know I did. :smile:

If my friend in the picture removes his hand from the light pole he will be exposed to a step potential of about 13 volts.

 

[mivey]

I know I did. :smile:

If my friend in the picture removes his hand from the light pole he will be exposed to a step potential of about 13 volts.

If you do that to your friends, what would you do to your enemies? And they have to put up with you calling them dairy cows.:smile:

FWIW you will see, at least for this reference, in section 9.2.7 that they used a 1 meter step distance. So your 13 volts (or 6.5 volts/ft) becomes a step voltage of 21.3

 

[iwire]

that they used a 1 meter step distance.

Metric ...... that is the work of the devil. :grin:

 

[mivey]

Metric ...... that is the work of the devil. :grin:

I agree. This is America!

We have to get DOT utility permits. At one time they were going to covert to the metric system. The DOT engineer told me he even thinks in metric (liar!) and lapsed back into feet and inches further in the discussion. Now we are back to feet & inches. I can't imagine how many of my tax dollars went toward that conversion nonsense.

 

[Dickieboy]

Thanks for all the info guys ,just what I needed,,,,,,,,,,,,,ivey thanks for the post deletion,my system didn't respond very fast to the first one and I thought I had forgotten to enter it.

dick