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Short Circuit Current Withstand Capacity

12/12/2017 11:31 AM

The Short Circuit MVA level of a 132/33kv substation is 20.31pu on 100MVA base. 2 x 60MVA Transformers were installed in the substation and the two packed up within a very short time. What factors do we consider in choosing a transformer for this substation please.

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#1

Re: Short Circut Current Withstand Capacity

12/12/2017 11:32 AM

What I want to know is whether the fault level of a substation has any effect on the choice of transformer to be installed at that substation. In this case the fault level of this substation according to my calculation is about 35KA while the short circuit withstand current rating of the transformers is 3.2KA for 2 seconds. Can a Manufacturer produce a transformer of 60MVA, 132/33KV rating that can withstand 35KA short circuit current

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#2
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Re: Short Circut Current Withstand Capacity

12/12/2017 11:46 AM
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#4
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Re: Short Circut Current Withstand Capacity

12/12/2017 1:34 PM

You should talk to a transformer manufacturer about this.

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#6
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Re: Short Circut Current Withstand Capacity

12/12/2017 4:08 PM

Jeez. Ask an expert!

  • ABB (company)
  • Crompton Greaves.
  • Bharat Heavy Electricals Limited.
  • SPX (company) transformer solutions in USA.
  • JSHP transformer in China.
  • Xian Xiandian Transformer in China.
  • TBEA Shenyang Transformer in China.
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#7
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Re: Short Circut Current Withstand Capacity

12/13/2017 3:28 AM

<...Can a Manufacturer produce a transformer of 60MVA, 132/33KV rating that can withstand 35KA short circuit current...> That's why the telephone was invented: so that one can ask questions and obtain answers to them.

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#3

Re: Short Circuit Current Withstand Capacity

12/12/2017 1:21 PM

My first concern is why you're not talking to your licensed electrical engineer about this?

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#5

Re: Short Circuit Current Withstand Capacity

12/12/2017 4:06 PM

you mean packed up, as in burned up and packed up and sent back to manufacturer?

I would say you bought them. Who does stuff like this, and turns around asks an anonymous forum for answers? Are you looking for permission to blame the OEM for your mistakes?

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#8

Re: Short Circuit Current Withstand Capacity

12/13/2017 2:45 PM

Some important factors include:

How the transformer(s) are connected,

The impedance of the transformers,

What they are feeding, etc., etc.

And most importantly; what the professionally prepared load-flow and short-circuit studies concluded, as well as how well the specification was written.

Turning 2 60MVA transformers into scrap copper and iron can be a SCLM (Severely Career Limiting Move).

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Re: Short Circuit Current Withstand Capacity

12/13/2017 11:04 PM

True but one it does make for a memorable display.

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#10

Re: Short Circuit Current Withstand Capacity

12/14/2017 1:52 AM

I think there are some confusions in data interpreting.

If the S1=20.31 p.u. from 100 MVA it is 2031 MVA short circuit level.

This it is for 33 kV system.[Usually it is 1000-1500 MVA maximum].

However, since is for 2*60 MVA parallel on single transformer will be only 35.5/2=17.75 kA [still very high for 60 MVA [6% short-circuit impedance!].

In my opinion, it is calculated for infinite power 132 kV system also.

The system at 132 kV presents usually a 8000 MVA short-circuit apparent power

that means also 8000/sqrt(3)/132=35 kA.

According to IEC 60076-5 Ability to withstand short circuit for instance, the rated short-circuit current is calculated on HV side so Isc132kV=2031/2/SQRT(3)/132=4.44 kA. That is still more than 3.2 kA for 2 seconds as declared by manufacturer.

A minimum short-circuit impedance for 60 MVA transformer it has to be 11% [according to the same standard]

A correct calculation it has to include the system impedance Z=132^2/8000=2.178 ohm and

the one transformer impedance 132^2/60*11%=31.94 ohm.

Then the considered current has to be Isc=132/sqrt(3)/(2.178+31.94)=2.234 kA

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