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FADHEL
Commentator

Join Date: Sep 2012
Posts: 58

Groundig Resistance

11/14/2012 3:51 AM

Dear all

please we need help

we requested buy auto transformer with specification below

(400/132/11)kv ------250MVA ----Tertiary winding is delta connected

with suitable resistance

The company sent a specification for grounding resistance and asked us to ratify, as follows

Neutral voltage 11kv----rated voltage 6.45kv----resistance 21.1 ohm----rated fault current 300A------rated fault time 30 sec ----insulation level 12kv

Are there other specifications must be requested from the company and on what basis chose the value of the resistance 21.1 ohm

Regards
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PWSlack
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United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
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#1

Re: groundig resistance

11/14/2012 3:58 AM

Oh, come on. Surely this is a telephone call to whomever produced the quotation?

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Joshi
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Join Date: Oct 2007
Location: India
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#2

Re: grounding resistance

11/14/2012 4:41 AM

I would invite the company representative for a technical discussion, and get everything thrashed out. Record the MOM for future reference.
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7anoter4
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#3

Re: Groundig Resistance

11/20/2012 4:52 PM

The supplied network capacitive current will state the rated grounding resistor current. The capacitive reactance of the supplied

network has to be about one third of phase-to-ground total capacitive reactance. See:

http://www.google.co.il/url?sa=t&rct=j&q=ungrounded%20system%20neutral%20grounding%20resistance&source=web&cd=1&cad=rja&sqi=2&ved=0CCcQFjAA&url=http%3A%2F%2Fwww.geindustrial.com%2Fpublibrary%2Fcheckout%2FWhite%2520Papers%257CSystem%2520NGR%257Cgeneric&ei=cfWrUK2bHszcsgasmYBI&usg=AFQjCNGi1EYeVE1aSs1kP34OPCzNW5o6HQ

So if 3*ICO=300 A then ICO=100 A ; XCO=6.45*1000/100=64.5 ohm; R<=64.5/3=21.5 ohm.

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7anoter4
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Location: 100 miles North from the World Center
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#4
In reply to #3

Re: Groundig Resistance

11/21/2012 12:06 AM

Sorry! The phrase:

"The capacitive reactance of the supplied

network has to be about one third of phase-to-ground total capacitive reactance"

has to be:

"The grounding resistance has to be less[or equal] than a third of total phase-to-ground capacitive reactance of the supplied network."

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