Feeds from transformer secondary

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mull982

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We have a 25MVA Utility transformer at our plant which has a 4160V secondary feeding the main distribution system to our plant. The secondary size of the transformer has a 4160V aerial bus from which 10 runs of 1000MCM are are run down to our main 3000A 5kV breaker lineup.

We are wanting to add another small crushing plant here to our site and were thinking about tapping off of this utility transformer to power this new plant. This new plant will only have a load of about 3000kVA or so. We want to keep the power feed to this new plant seperate therefore do not want to feed it from anywhere on our existing distribution system. Therefore we are brainstorming how to tap a new feed of or our transformer secondary bus to feed this new plant.

What question involves the proper way to tap off of this secondary transformer bus? Can I just tap the necessary feeders off of this bus, and have the bus feeding both plants with the main breaker lineups for each plant downstream of the bus (1000ft each). Or can I only have one feed coming off of this transformer bus and bring this to another main breaker lineup to then feed both the existing and new plant? The reason this issue is confusing to me is because on the transformer secondary bus there is only differential protection and the and no breakers to distribute the different loads, like I mentioned the existing main breaker to the plant is located 1000ft away.

Can anyone assist with the proper method for doing what we are trying to do. Are there code examples that apply to this application.
 
I was reading some more information on this subject and was wondering what the difference between a transformer secondary tap, and a secondary feeder.

It sounds like if there is no seconcary overcurrent protection at the transformr itself then any secondary conductor leaving the transformer is considered a tap conductor?

If there is secondary protection at the transformer iteslf then any secondary conductor leaving the transformer is considered a feeder conductor?

If this is the case, then it sounds like a feeder conductor can feed multiple other circuits where a tap conductor cannot. A tap conductor must go through an OCPD.

What would bus directly conneced to the secondary of transformer windings be considered?
 
I don't understand the original post.

where's the metering ? (is the metering at the transformer and the service feeders belong to the plant ? if the feeders are poco and the metering is at the MDP then the taps are also feeders, not under NEC ?) also if the feeders are outside, then the outside (unlimited ) tap rule applies, correct ?
 
Having gone through this a couple of years ago (caution - opinion to follow): It matters not so much where the meter is, nor who bought the xfm. Mostly it matters where you and the utility decide the service point is.

If the service point is on the xfm primary, then the xfm secondary falls under under the outside unlimited length rule, then the secondary terminates in a single set of OCP.

edited to add: I think that's what nak and mull were getting at.

carl
 
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nakulak said:
I don't understand the original post.

where's the metering ? (is the metering at the transformer and the service feeders belong to the plant ? if the feeders are poco and the metering is at the MDP then the taps are also feeders, not under NEC ?) also if the feeders are outside, then the outside (unlimited ) tap rule applies, correct ?
Click to expand...

We own the transformer and substation yard which it is in. The metering is on the bus of the secondary transformer, and yes the service feeders belong to us.

The thing that is confusing me is that off of the secondary bushing of the transformer there are cables, which then go to a bus which then the undergournd conuctors are attached to going down to our main breaker. To me it seems that the cables and bus are all part of a secondary tap feeding off the secondary of the transformer.
 
mull982 said:
We own the transformer and substation yard which it is in. The metering is on the bus of the secondary transformer, and yes the service feeders belong to us. ...
Click to expand...

Sounds pretty normal for industrial. I don't think the secondary metering matters - service point is probably the xfm primary disconnect.

mull982 said:
... To me it seems that the cables and bus are all part of a secondary tap feeding off the secondary of the transformer.
Click to expand...
I would pretty much agree with that - might word it a little differently.

Opinion: Falls under 240.21.C.4 (2005)

carl
 
Is busbar on the secondary of a transformer considered an extension of the transformer secondary, or is it considered part of a secondary tap conductor?
 
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