Fault Current

[gregoryfast]

I am putting together an Excel spreadsheet of transformers in our system. I wanted to come up with a formula to automatically calculate the fault current from the name plate data. Does anyone have a simple way of doing this?
If it can be to the nearest 1000 amps, that would be OK.....
I have seen a website (oberon) that has a calculator when you enter the name plate data. It does it for you. But it would take a long time for me to enter each transformer separately.
Also, is there a standard distance for giving the value of the fault current?

 

[bennie]

Re: Fault Current

Calculation is required at the line terminals of the equipment.

I have never witnessed damage to equipment, from a fault, other at the location of the fault.

Don't tell me that the AIC rating of equipment is forever. What is the big deal with fault current calculations?

There is a lot of equipment breaking down and degrading. It's a fact of life and a law of physics.

 

[ron]

Re: Fault Current

Are you refering to a calculation the produces the available fault current at the secondary terminals of the transformer based on an infinite primary fault current? These are very conservative, and the results will cost you more in higher equipment ratings than if you had a study done properly.
If you insist:
See http://www.bussmann.com/library/docs/EPR_Booklet.pdf
Page 7 and
Page 9, Table 5

 

[bob]

Re: Fault Current

If you are interested in an estimate of the fault currrent assuming an infinite fault capacity the following will do the job
% R, %X and %Z are name plate info
Trans X(ohms)=(10)(%X)(Sec volt KV)?/Trans KVA

Trans R(ohms)=(10)(%R)(Sec volt KV)?/Trans KVA

ZTotal = Sq Root(R? + X?)
Isc = Sec Line Voltage/(Zt x 1.73)
If you goto Mike Holts Home Page and look under free stuff there is a fault caculator you can download.

[ July 17, 2003, 12:07 AM: Message edited by: bob ]

 

[ron]

Re: Fault Current

Also, for infinite primary calcs you can use:
Isc=transVA/V/trans impedance

So for example, a 300kVA transformer with a secondary voltage of 208/120V and an imperdance of 3%, the calc looks like:

Isc=300000/208/1.73/.03=27790A

 

[gregoryfast]

Re: Fault Current

Thanks Ron,
That was what I was looking for.