Transformers and 3ph Delta v Wye

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artherd

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It's late, so please pardon the scattered post.

A client has an older 3-phase Delta "High Leg" 200A service.

They have a large site, and want to run power to the top of the property.

We are looking at a pair of 600V (possibly 2400V or even 4160V) step-up, and step-down transformers to take the voltage the requisite distance with acceptable drop.

We are acquainted with MV and certified in it's use and requirements.

What I'm not so familiar with, is what the heck to do with this high-leg system, and how that affects my transformer selection. Can we use Wye transformers? I generally deal with step-up or step-down, not step-up/down within the same system. We would need a neutral conductor at the top of the property. Can we generate that in the step-down transformer? Over a 50 acre parcel, could we classify this as service conductors, or are we under standard feeder/sub-panel procedures after the utility meter? (neutral & ground in cable)
 
artherd said:
What I'm not so familiar with, is what the heck to do with this high-leg system, and how that affects my transformer selection.
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The high-leg is of no concern, you are just taking three hots to the step up transformer.
We would need a neutral conductor at the top of the property. Can we generate that in the step-down transformer?
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Yes. XO on the secondary.

Over a 50 acre parcel, could we classify this as service conductors,
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No, those only come from the POCO.

or are we under standard feeder/sub-panel procedures after the utility meter? (neutral & ground in cable)
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Yes.
 
JMO, but 50 acres is not that big, especially if you only have a 200 amp @ 240 volt three phase supply, I would thing it is a little hard to justify the expense of over 600 volt equipment and the fact that not as many people would be qualified to work on it if needed.

Around here we run 480 volts to field irrigation equipment all the time and at higher capacity levels then what you mentioned, and generally because it cost more to run over 600 volts then it cost to run 480 volts. We are looking at 160 acre square plots most of the time, with the load served at about the center (gives us around 1300-1400 feet of underground most cases). If your 50 acres is square shaped and you ran from one side to the other it would be in the same length range as most of these irrigation installs and around the median capacity of many of them.

If you want to bring medium voltage across this property may want to see what it will take for the POCO to just provide an additional service at the other end. May or may not work out but doesn't hurt to find out what it will take, or if they will even do it.
 
hardworkingstiff said:
If the PoCo is using an open Delta, is there a chance of causing them some problems?

Should I assume you have spoken with the PoCo and they won't extend their primary to that area?
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That's my concern. The PoCo feeds the site with a Delta 208v 3? 4W service with neutral. Can we safely tie that neutral to another delta connected step-down at the end? (I believe code is going to require us to do so, but then 250.30(A)(1) and others appear to allow simply running A, B and C conductors, no EGC, no neutral? )

If I am required to run a bonded neutral, can it be the same as the MV (or 600v if we go that route) conductors?

Circuit run is about 2,000 feet.


PoCo won't run a primary any further, I have asked.
 
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You are giving a somewhat contradictory description of the service. The only way POCO can supply a neutral conductor, as distinct from an unrelated grounded conductor/earth conductor, is if the really have a wye source or are using something like a zig-zag winding set to create a neutral point from a delta source.
And the only way a true delta can be provided, under the NEC, is ungrounded or corner grounded. Or with a true or derived wye neutral which is impedance grounded.

Tapatalk!
 
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artherd said:
That's my concern. The PoCo feeds the site with a Delta 208v 3? 4W service with neutral.
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That sounds like a wye service.
Can we safely tie that neutral to another delta connected step-down at the end? (I believe code is going to require us to do so, but then 250.30(A)(1) and others appear to allow simply running A, B and C conductors, no EGC, no neutral? )
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You don't use a neutral on the primary side of your step up or step down transformer. You do bond the derived neutral on the secondary side per 250.30. You must have an EGC, it can be wire or conduit and some kind of bonding jumper at the tranny or first disco.
If I am required to run a bonded neutral, can it be the same as the MV (or 600v if we go that route) conductors?
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Don't know about MV.
 
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