Short Circuit Current Capacity of Transformers Bushings During a Fault

Get them to change the requirement, however if it is a requirement rather than just an over-rating then offer the right bushings or get proof the bushings you want to supply will actually meet the customer's requirements.

A call through to the bushing supplier may quickly clear things up.

http://www.slideshare.net/eqbal_asif/power-transformers-principlesandapplication

Yours doesn't have the pretty colors mine does.

Yeah, but it's "cooler"!

I know next to nothing about transformer bushing, but at a guess I would say the short circuit current will manifest itself as breakage (insulators?) by expansion due to heat, or melting of conductors due to heat, or mechanical stress due to magnetic forces.

Whatever the risk might be, the potential source of heat at the bush is 63kA x resistance of the bush. If the 20kA bush has much lower resistance then it might be OK heatwise.

But don't take my word for it. Being a devout coward, I would supply what the customer asked for.

See :

IEC 60137 Insulated bushings for alternating voltages above 1 000 V ch. 4 Ratings.

The transformer bushings need not be rated for the system fault level. Rather, these are rated to withstand the through fault current at the bushing terminals of the secondary windings.

If through fault current is calculated from the transformer rating particulars, that could be the basis for explaining to the client.

I agree with raghun.The transformer bushing does not have to withstand the System short-circuit current. According to IEC 60137 Insulated bushings for alternating voltages above 1 000 V ch. 4 Ratings.

If the rated loading current is 4 kA [or more] Ith=100 kA for 2 sec.

If the rated loading current is less then Ith=>25*Irated

The USA equivalent standard-I think-it is:

ANSI/IEEE Standard C57.19.00-2004

Since I don't have this standard with me I am not sure what this standard recommends.