Substation XFMR high side fuse coordination with low side recloser (XFMR damage curve confusion)

[R10_]

Hello all.

I am trying to coordinate a high side fuse with a low side recloser, but the issue I am having is that the fuse I have chosen does not protect the XFMR's damage curve all the way, about 100A-300A of the xfmr curve is left unprotected. However, my fuse curve lays between the cold load inrush and damage curve. Anybody have some tips that I may need to consider? an yes I have tried multiple different fuses, however not much success.

 

[synchro]

The overload region of the current is typically protected on the secondary side, with the primary fuses providing short circuit protection.

 

[R10_]

The overload region of the current is typically protected on the secondary side, with the primary fuses providing short circuit pr

Umm ok?

 

[David Castor]

It's difficult to provide full range through-fault protection for a delta-wye transformer using only primary fuses, so your situation is a common one. There's no legal requirement to fully protect a transformer against its damage curve. You do the best you can. If you can't live with that you can install a circuit switcher instead of the fuses. As synchro mentioned, any secondary fault in a feeder should be cleared by the recloser well below the transformer damage curve.

 

[paulengr]

Umm ok?

Set the recloser to match the transformer damage curve. This protects against load-induced damage (overloads). There is no way to overload within the transformer itself so only short circuit protection and possibly ground fault is needed. IEEE C series standards call for 87 (ground fault) relaying starting at 10 MVA.

You can’t coordinate fuses with magnetizing current and expect to cover the damage curve at low currents.