Transformer Protection

[rscinsc]

I have an interesting problem / question. I can't find this exact scenario in another post....so I thought I would try a new post.

I am retro-fitting an installation, that was installed under the 1993 NEC.
The basics are:
A single transformer rated 13.8kv primary / 575 VAC secondary @ 2200 amps. This transformer has a primary fused disconnect and no direct secondary protection (the secondary has CTs, that trip a 13.8kv Circuit breaker that feeds this, and other transformers).
After the CTs, on the secondary side that transformer has two parallel feeds, each feeding a 2500 amp breaker (each breaker feeds a large DC drive).

My questions:
1. Using the 2005 NEC can I still use only these CTs for secndary protection (the transformer sits outside, and feeds the drives inside about 50' away).
2. Can I replace the 2500 Amp circuit breakers with 2000 Amp breakers OR do both breakers need to be able to take and interrupt the full 2200 amps?

Thanks,

 

[jim dungar]

I have an interesting problem / question. I can't find this exact scenario in another post....so I thought I would try a new post.

I am retro-fitting an installation, that was installed under the 1993 NEC.
The basics are:
A single transformer rated 13.8kv primary / 575 VAC secondary @ 2200 amps. This transformer has a primary fused disconnect and no direct secondary protection (the secondary has CTs, that trip a 13.8kv Circuit breaker that feeds this, and other transformers).
After the CTs, on the secondary side that transformer has two parallel feeds, each feeding a 2500 amp breaker (each breaker feeds a large DC drive).

My questions:
1. Using the 2005 NEC can I still use only these CTs for secndary protection (the transformer sits outside, and feeds the drives inside about 50' away).
2. Can I replace the 2500 Amp circuit breakers with 2000 Amp breakers OR do both breakers need to be able to take and interrupt the full 2200 amps?

Thanks,

Yes, relaying on the secondary continues to meet the requirements for secondary protection. Because of this, your load breakers may be sized independent of the transformer full load output current.