Transformer Feeder Sizing

[PARod]

We have a double-ended substation with 2 ea.- 2000kVA transformers, main breakers and a tie-breaker on the secondary side. Each transformer is currently fed with a 350MCM cable from different sources.

Our plant is now closed, but this substation will stay forever (superfund site). The loads on each side are less than 200kW and there is zero chance of the loads increasing.

The source supplying transformer A is going away. I could move the loads from the A side to the B side; I could run another feed (.25 miles on poles) from the same sub as the B is fed from.

Or to retain the flexibility of having 2 transformers, I could use the same feed as the B transformer by installing a jumper from the line side of the B transformer disconnect switch to the line side of the A transformer disconnect switch. The 350MCM cable would be large enough for the total loads on both transformers. Is there any thing in the code that would allow me to do this?

 

[dpc]

I don't think there is anything in the NEC that would prevent you from doing this, if the current installation meets the NEC.

On the other hand, if the plant is closed, why do you need both transformers? If you keep both energized, you are paying for core losses 24x7 on two vastly oversized transformers. You might as well reduce that to one vastly oversized transformer. If you don't keep the other transformer energized, you run the risk of moisture getting into the windings. You might think about selling one of the transformers.

 

[RRaghunath]

PARod,

How important are the loads connected?

How do you propose to feed the loads when the lone transformer goes for maintenance shutdown?

How do you address the possibility of power failure due to the cable on LV side going defective?

These are some of the questions that come to my mind that need to be addressed before making decisions such as the present one.

Hope it is helpful.

raghunath_n00@rediffmail.com