%IMPEDANCE CALCULATION OF TRANSFORMER 1

[28021984]

Dear Sir

Please let us know what is the relation between %impedance ,BIL & short circuit current of the transformer

 

[davidbeach]

No relationship involving BIL. Inverse relationship between impedance and short circuit current.

 

[28021984]

Thank you for your response.

i want to know the relation between impedance and short circuit current.

if possible kindly send me the formula

 

[rcw retired EE]

Short Circuit Current = (Transformer Full Load Amps)/Zpu.

Where:

Tx FLA = the full amps at the base transformer rating, and

Zpu = per unit impedance of the tranformer= 100 x %Z.

Example: short circuit through a transformer with 10%Z will be 10 times its full load amps, assuming it is fed by an infinite source.

 

[waross]

Testing and rating is done with the transformer at operating temperature. A cold transformer will test with a slightly lower impedance. With small dry type transformers (less than 10 KVA) the difference is noticeable.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davidbeach]

assuming it is fed by an infinite source

Very common assumption, very uncommon source.

If you're talking big transformers at high transmission voltages it can be a reasonable assumption. If you're talking small transformers connected into the distribution system it may not be such a good assumption.

 

[VTer]

also Zpu = %Z/100

"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic — and this we know it is, for certain — then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". – Nikola Tesla

 

[wareagle]

Quote by DB
"If you're talking big transformers at high transmission voltages it can be a reasonable assumption. If you're talking small transformers connected into the distribution system it may not be such a good assumption. "

True but many utilities will use this when giving a fault current value to a customer.

 

[rcw retired EE]

"also Zpu = %Z/100 "

Thanks for the correction.

Isc = FLA /Zpu = (FLA x 100%)/%Z

 

[erputra0615]

ok..prends i have the calculation of tansformer impedance..
ithink its good for us