Fusing

[KVX10]

I am in a debate concerning fusing for a distribution system as far as wire and padmount transformers are concerned. There are two schools of thought here. One says to fuse to protect the wire and rely on the bayonet fuses within the padmount transformer, the other says to fuse to protect the padmount transformer, while being aware of the capacity of the wire installed(primary).

I'd like the opinion from those in this forum.
Thank you.

 

[jghrist]

Where is the fuse? You would normally want to coordinate the line fuse with the transformer bayonet fuse so that for a transformer or through fault, only the bayonet fuse would blow. If the line fuse is on a tap to only one transformer, the coordination is not important.

The transformer fuse will protect the transformer. The line fuse needs to protect the wire, but this is normally not a problem. The line fuse needs to be small enough to coordinate with upstream fuses, reclosers, or breakers.

 

[dpc]

If the only load on the overhead fuse is the transformer, I probably rather blow it before the bayonet fuse in the transformer, but maybe that's just me.

I agree it the line fuse serves other loads, you'd rather have the bayonet fuses go first, just to minimize the outage. This assumes that all your padmount xfmrs have internal fusing. Many do not.

 

[waross]

If we are considering overhead lines, the majority of faults will be birds, branches and "critters". The transformer fuse will not be involved. The transformer fuse should operate on transformer faults and overloads. The line fuse should hold in on faults long enough to allow the re-closers to complete their cycle.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[KVX10]

The fuse would be on a "dip pole" radial feeding padmounts. Coordination is what is most important in most cases as jghrist responded. Thanks for the input.