GSU Protection

[nhcf]

Facility has (2) 4160 VAC synchronous generators each tied to 5KV bus through individual generator breakers. 5 KV bus is tied to LV connection of GSU transformer. HV of GSU transformer feeds 15 KV breaker and connects to utility.

Does this GSU fall under the requirements of NEC? If so how are the requirements of 450.3(A) transformer overcurrent protection applied? I assumed the LV is the 'primary' - why isn't a dedicated OCPD required on the LV side of the transformer?

 

[davidbeach]

What kind of "facility"? Does the NEC apply? I wouldn't if this is a utility generation plant.

It's been a while since I've needed to check NEC requirements, but 4160V requirements are different than 480V requirements. Also, the NEC is really written around sensing and interruption being in the same device, such as your typical 480V breaker. In your installation, just guessing since you didn't provide a full one line diagram, the transformer relays may be using CTs on the generator side of the two generator breakers and either summed in the field or summed in the relay. In either case it is easy to provide the level of protection required by the NEC, just a bit differently.

 

[nhcf]

facility is non-utility, distributed generation plant. The transformer protection is configured as you describe (relays on gen side of gen cb's). I agree the relaying is providing the 'protection required by the NEC'. But if this site needs to meet the NEC, then I am not sure that it meets the requirement for protection detailed in 450.3(a) for transformers > 1000V on primary and secondary.