PACKAGE SUBSTATION 13.8 KV/220V 3 PHASE WITHOUT MAIN BREAKER AT SECONDARY.

[Anwar Pasha]

The package sub station has input 13.8 kv and the sec is 3ph 220 v. The sec does not have main breaker.
What shall be the short circuit rating of branch breakers.Is there any relation of such rating with the main busbar.

 

[charlie b]

You can't calculate the short circuit current without knowing the KVA rating of the transformer and its percent impedance. Do you have that information?

 

[kingpb]

If this is truly a packaged substation; i.e. came from one manufacturer as a unit , then they should have taken the short circuit rating of the LV bus into consideration. Regardless, the manufacturer drawings that would have been provided for review and acceptance prior to fabrication would have that information on them and certainly will be on the final drawings shipped with the equipment. The SC rating would be the same as the bus.

 

[Anwar Pasha]

The package sub station has input 13.8 kv and the sec is 3ph 220 v. The sec does not have main breaker.
What shall be the short circuit rating of branch breakers.Is there any relation of such rating with the main busbar.

The transformers are rated 1000 KVA.

 

[kingpb]

Assuming an Impedance of 5.75%;

In ANSI/IEEE US standard ratings would be 65KA.

In IEC I believe it would be standard 50KA.

 

[Tony S]

This is the LV end of a UK packaged substation, there are no busbars to worry about as the manufacturers have type tested them. The maximum fault level would be 45kA, the fused output ways are rated for 80kA.