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akpanda74
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Join Date: Oct 2012
Posts: 7

Do We Need To Calculate Touch & Step Potentials ?

09/16/2014 2:43 AM

We have a receiving substation (220kv/33kv/11kv,3-winding) which feeds power to one 1.6MVA (11kv/0.433kv ,Dy) through 11kv cable (85m) to a plant load centre. The plant load centre equipment earthing has been provided with a number of earth rods driven into the ground arround the plant building and connected together. The load center transformer neutral is grounded separately. In this configuration , do we need to calculate Step & Touch potentials at the plant (as the source 11kv is local ) and if yes , how I will use IEEE 80 to calculate Earth grid resistance (Rg) as it is not a grid rather a hollow square.
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7anoter4
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#1

Re: Do we need to calculate Touch & Step Potentials ?

09/16/2014 5:55 AM

In the 1.6 MVA transformer zone a short-circuit phase-to-ground-to-phase could raise the local grid GPR. On the other hand the transferred potential has to be reduced to tolerable. [See IEEE-80/2000 fig.13 ch.8.2 Typical shock situation].

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7anoter4
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#2
In reply to #1

Re: Do we need to calculate Touch & Step Potentials ?

09/16/2014 10:15 AM

This is a possible scenario:

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The.Tinkerer
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#3

Re: Do We Need To Calculate Touch & Step Potentials ?

09/16/2014 10:20 AM

You already have a commissioned substation and have not bonded the neutral of the "load center transformer" to the ground ring.

Is IEEE 80 all you have to go on? That's a guide, not a set of directives, rules, and regulations. Please provide an example of your "hollow square".

Why have you just now decided to even consider calculations or safety precautions for this? That should have been done before commissioning.

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7anoter4
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#4

Re: Do We Need To Calculate Touch & Step Potentials ?

09/27/2014 11:50 AM

What did you mean by "as the source 11kv is local"? If the transformer and the low-voltage consumers are standing on the Substation 230/33/11 kV grounding grid you don't need to calculate the touch and step potential separately since no current will leave [or enter] these facilities through grounding grid.

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