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farmson
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Join Date: Jan 2010
Posts: 3

Short Circuit Calculation

02/12/2010 7:26 AM

" how do I calculate the short circuit current for selection of VCB for transformer of 2000KVA, 11/0.42 KV with 7% impedance."
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iafify
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Join Date: Feb 2010
Posts: 1
#1

Re: Short Circuit Calculation

02/12/2010 7:52 AM

Z= (USc * U)/(100*S)

Isc= U/(√3 Z)

Usc=transformer impedance in % percentage

S= Rated power in KVA

U=Rated (low voltage) system voltage
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farmson
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Join Date: Jan 2010
Posts: 3
#4
In reply to #1

Re: Short Circuit Calculation

02/13/2010 1:35 AM

Thanks iafify... Really it's working.
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wareagle
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Join Date: Jun 2008
Location: Alabama
Posts: 1604
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#2

Re: Short Circuit Calculation

02/12/2010 7:13 PM

The correct way http://ecmweb.com/mag/electric_shortcircuit_calculation_methods/

Infinite Bus Method http://www.brainfiller.com/articles/infiniteBusMethod.php
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jraubsr
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Join Date: Sep 2009
Location: Houston, TX
Posts: 118
#3

Re: Short Circuit Calculation

02/12/2010 8:24 PM

Estimated method, divide the voltage by the impedance. I=e/z

__________________
 Thank you for your help - By far the best info site!
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Anonymous Poster
#5

Re: Short Circuit Calculation

02/13/2010 3:53 AM

Hope, u'll use the VCB at 11KV end. So F.L. current in primary side Ip= 20000/11*1.732

= 1050 A

Short Circuit current Isc= 1050/0.07= 15KA

So u may select VCB of 1200A normal current and atleast 20KA SC current for 3 sec.
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Anonymous Poster
#6

Re: Short Circuit Calculation

02/13/2010 7:38 AM

You are having a 2MVA , 11KV/420V transformer ? (only in homeworks we write 0.42KV) and you want us to calculate the protection rating.

Sorry, I don't want to get involve in a legal dispute. Only

a) It is a homework (probability 0.99)

b) It is suicidal/ homicidal (probabilty 0.01)

c) Any other (probability 0)
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farmson
Participant

Join Date: Jan 2010
Posts: 3
#7
In reply to #6

Re: Short Circuit Calculation

02/14/2010 11:34 PM

Sorry boss, I get what you want....

This place is for everybody who want to know everything related to Electrical Engineering...

And if you know(you can assume in percentage also), I am doing my home work... then great....

But i am confused!!!!!why r u as a guest.... please join and be an active participant..
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wareagle
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Join Date: Jun 2008
Location: Alabama
Posts: 1604
Good Answers: 63
#8

Re: Short Circuit Calculation

02/14/2010 11:49 PM

farmson quote "Thanks iafify... Really it's working."

What does that mean? That method does not give a correct answer. It gives the maximum possible fault but not the correct value of the actual fault.
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