Substation LV Distribution Scheme

[Power0020]

In a substation, the LV system is composed of two redundant auxiliary transformers with two incomer CBs and bus tie CB to support N-1 system security (2/3 ATS). However, when connecting sub-distribution boards with one incomer feeder the system security on the subs will be just N. Some local utilities require a duplicate redundant incoming feeders from main AC/DC DBs two buses to subs to keep the downstream security at N-1 level as well.

If the local standards don't require this duplication and the contactor is not happy to do so (extra cable+2 CBs+ATS cost), the downstream loads / subs will be left with N security, the contractor justifies his point as most of loads has only one supply! but I personally think that it will waste the idea of Aux.transformer redundancy in case of bus fault.

any clues?

 

[rterickson]

What does your specification/contract/drawings say?

If it's not required by code, and you didn't specifically require it, why do you think the contractor should have to pay for it?

 

[Power0020]

nothing is mentioned in the contract other than duplicate main supply.

Does this imply the requirement of duplicate supply for all other sub-distribution boards?