Protection of feeder cables

[Mbrooke]

I've never seen it before, but what do utility engineers think of 400E protection for underground feeder circuits? 13.8kv, 7.5MVA feeders. Every previous installation that I have seen has been relayed breaker and I am having a hard time understanding the benefit of this new scheme.

 

[davidbeach]

Sounds like protection for a tap downstream of the substation. Does not sound like something to be done at the substation.

 

[Mbrooke]

Its being done at the substation- at least being proposed. Protecting the feeders with fuses instead of breakers.

 

[dpc]

I've seen it in rural substations. Only benefit is low cost. A totally UG feeder does not benefit much from reclosing, since faults are almost always permanent. But many feeders leave the sub UG only to pop up OH a short distance away.

 

[davidbeach]

Along with not reclosing, the event reports from fuses leave a bit to be desired...

 

[Mbrooke]

Tell me more about these rural subs. Were they underground? Or just tree wire overhead? No overhead will be present on these feeders so no need to reclose.

 

[marks1080]

LMFAO @ davidbeach

now there's coffee on my shirt....

 

[Mbrooke]

@mark1080: no need, thats where thumpers and fault indicators come in

 

[dpc]

Generally old, small substations - sometimes Co-op, sometimes small municipal. Transformer primary protection was fuses and two or three feeders. One small muni we dealt with had no battery system in their substations and didn't want any.

Another fairly common design was to provide feeder reclosers with bypass fuses.

The feeders were not strictly UG.

Yes, they all love their thumpers.

 

[Mbrooke]

I'm surprised its not more expensive when protecting overhead lines considering you need to spend $300+ per power fuse- that is unless they have infrequent feeder faults or they are using simple fused cutouts. Any load break switches in those substations by chance?

The proposed approach for this substation is similar, 69kv 25MVA fuse protected transformers, load break switches and metal clad MV with load breaks and fuses. This substation will probably not have batteries either. I like the approach, just odd from what I am used to seeing. Cost savings are very attractive however.