Dual Transformer Fusing

[Jeff Mabry]

I am working on a factory installation in the Philippines which has a bank of 2 - 2MVA 13.8kv / 460v transformers feeding the factory. The local power company installed separate fuse links to each transformer. The transformer company wants a single line fuse to both.

The secondary is connected to a bus inside the sub-station which feeds a 4000 amp main inside the utility room.

My interpretation of NEC 450.7 is that the parallel transformer bank (4 MVA, 13.8kV/460V) with a single 170 A fuse per line protecting the primary bank meets the requirements given in Table 450.3(A) for use in a supervised location. Is this interpretation correct?

Thank you,
Jeff Mabry

 

[bdarnell]

I have designed a few substations using parallel transformers and have never used a single line fuse for both transformers. The transformers need to be switched as a unit, but protected individually. I wouldn't think you would want to have the entire facility down if you have to take a transformer off line for service or in the unlikely event of a fault.

This can be easily accomplished with a 3-way VFI on both sides of the transformers.

Hope this helps.