Network Transformer

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Many of those xfmrs have primary fuses either in the xfmr box or at the upstream source to protect the primary cable and xfmr. However, I also see a lot of protection relays w/ CTs that trip an upstream breaker being used.
 
How is it normally done in most utility applications? I guess what is throwing me off is the I cant find any manufacture documentations that fuses are built into these units.



In so far all the network transformers tap off a EPR cable which feeds at least 12 other network transformers. The cable is protected via oil substation breaker with inverse phase and definite time current ground curves. When a cable faults out the breaker trips and with it the network protector senses reverse flow disconnecting the transformer.


However, if a winding fault occurred, I am at loss as to how the unit is taken off the feeder, if at all.


Is there such thing as a none fused network transformer?
 
Some transformers do have in-tank fuses for catastrophic short-circuits, but I can't swear how common that is in network transformers.

While the network protectors will provide some measure of protection depending on how they're relayed, as far as I know the only true winding protection comes from the feeder breakers.

I've occasionally run into cute little SF6 breakers down in vaults used for primary protection where they wanted to sectionalize the circuit.

I've got a good white paper on the basics of network protection somewhere. I'll see if I can find it.
 
I'm not sure if you are referring to single phase residential padmount xfmrs or three phase type. The 3 phase xfmrs typically have fuses in the termination cabinet. The single phase residential xfmrs have the fuse inside the main box and not where the primary elbows or secondary paddles are.
 
big john said:
Some transformers do have in-tank fuses for catastrophic short-circuits, but I can't swear how common that is in network transformers.

While the network protectors will provide some measure of protection depending on how they're relayed, as far as I know the only true winding protection comes from the feeder breakers.

I've occasionally run into cute little SF6 breakers down in vaults used for primary protection where they wanted to sectionalize the circuit.

I've got a good white paper on the basics of network protection somewhere. I'll see if I can find it.
Click to expand...

I would be very interested! :D

That what bugs me, every other transformer like a pad mount has links and accessible bayonet fuses but in the case of Network transformers (at least these ones) I cant for the life of me see or find a fuse.

If these don't have fuses I may have to go that route.
 
Here's the paper I was thinking of, it's for a type of network protection from Eaton, but it gives a good rundown on a lot of the basics.

I had an epiphany while reading through this: The reason you're not going to find a network transformer with built-in primary overload protection is because it doesn't matter.

A network isn't going to be served with a single primary circuit. So in the event of a primary fault, the protector isolates the network from that feeder and the feeder breaker isolates the cable and transformer windings. This isn't a problem because by design the network has redundant interconnected sources that allow it to stay online.

If there were multiple network transformers coming off a single feeder, that's when primary protection would be critical on the transformers, because you'd dump the whole network on a single fault.
 
Ok that makes more sense. But in terms of a fault, couldn't a catastrophic failure result since the typical network feeder has to take many transformers into account? Ie, its like severally over fusing each transformer by 30x.


Link is being read up on, good resource! :D:cool:
 
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