Open delta with no primary neutral?

[tortuga]

I have 2 primaries of a 3 phase system and no neutral. Is it possible to run an open delta with no primary neutral? (it is a mile or so to the neutral)

 

[LarryFine]

Without using earth as the neutral, no.

 

[jim dungar]

A delta transformer connection requires at least 3 conductors, either 3 hots or 2 hots + 1 neutral.

 

[LarryFine]

There is a way to obtain 3 phase: a VFD or a rotary or static converter.

 

[gar]

100507-1846 EST

tortuga:

You do not need a neutral to supply power to a pair of transformers wired as an open delta secondary. Your question probably did not accurately define what you wanted to ask.

As was pointed out above you need three wires, and none have to be a neutral even if your source is a Y.

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[72.5kv]

You would have open delta/Open delta. Open wye/open delta is more common.

 

[LarryFine]

You would have open delta/Open delta. Open wye/open delta is more common.

Agreed. Delta-Delta loses one advantage of the open Delta - the need for only two of the phases.

But, you still do need that system neutral, which is almost always run with the phases anyway.

 

[tortuga]

Thanks everyone for the replies.
My goal is to serve some 3 phase and limited single phase loads where there are only 2 3∅ 12.5kv primaries and no primary neutral. The three phase load is the largest load at about 10HP.

You would have open delta/Open delta. Open wye/open delta is more common.

Are you saying the 2 3∅ primaries with no neutral can be connected in an 2 wire Open wye and the secondaries connected open delta? That is what I was picturing I did not know it was called Open wye/open delta.
In that case the primary neutral connection floats?
And the a secondary center tap neutral can be grounded to stabilize load side voltage to ground and feed some 120V loads?

 

[LarryFine]

Are you saying the 2 3∅ primaries with no neutral can be connected in an 2 wire Open wye and the secondaries connected open delta?

In that case the primary neutral connection floats?

Nope. Can't do it without the neutral. All you have is a single-phase line-to-line voltage.

And the a secondary center tap neutral can be grounded to stabilize load side voltage to ground and feed some 120V loads?

You can obtain 120/240 1ph with a single-phase source, whether its line-to-line or line-to-neutral.

You cannot obtain 3ph from a 1ph source. You must have three conductors from the source, either 2 lines and neutral, or 3 lines.

 

[jim dungar]

Agreed. Delta-Delta loses one advantage of the open Delta - the need for only two of the phases.

The primary advantage of the open delta is the ability to create it with only (2) single phase transformers. Among other things, less core = less core loses = more revenue for utility.

 

[tortuga]

Thanks everyone that settles it.