WYE to Double delta converting

[eleceng85]

Hi all
i has 3 phase wye connection 400V LL, 230V LN, 30KVA
i wanna make it single phase i read in the generator manual the best way to make it single phase is the double delta. my question is: when i make the connection double delta does this decrease the rating power
? or the generator will gives the same power when it was in WYE (3phase) connection.
3 phase wye power = 1 phase double delta power .... is that right ?

 

[ccjersey]

Not usually.

Unless the generator manual or spec tag specifically says the capacity is the same, you should assume the capacity is 20kVA single phase (2/3 of 3 phase capacity).

For many/most manufacturers, an "extended stack" is a special order option.

 

[eleceng85]

thank u so much for help

 

[ScottyUK]

You may find you can the full kVA capability of the alternator even at unity power factor, i.e. your revised capability diagram won't have the characteristic flat top which indicates the prime mover limit on most such diagrams. Of course that assumes that you don't install a smaller engine than was fitted when it was a three-phase set...


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If we learn from our mistakes I'm getting a great education!

 

[waross]

Your voltage will be 230:460 Volts.
Your current capacity will be the same.
Your KVA capacity will be 2/3 of the original rating.
You may run at unity power factor.
Your engine will have enough power to develop at least 120% of the allowed output for a standby set and over 130% of the allowed output for a prime rated set. Beware that you don't overload the set. There will be enough excess engine power available to damage the set if it is overloaded.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[waross]

If this is an older set, you may want to consider a zig-zag connection rather than a double delta. It is much easier to convert to a zig-zag connection if some of the wire markers are missing or illegible.
You should have line 1, line 2, line 3 and a neutral.
Open the neutral connection.
Locate the conductor(s) that has continuity to line 3.
Connect this conductor(s) to line 2.
Insulate this connection.
Take single phase power from line 1 and line 3.
The neutral is still the neutral.
This reconnection may be done safely even if all the wire identification tags are missing.
This was once the preferred single phase connection.
The performance is the same as the double delta connection.
Note, you should be able to locate the neutral point and it is safe to arbitrarily assign line numbers to the three phase leads for the purpose of this connection.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[genhead]

Bill,
I also remember when zig-zag was the preferred single-phase connection. Do you know why double-delta is now preferred?

 

[waross]

Probably because it is symmetrical but that's a guess.
Then there is the Collins or bar-diamond connection for converting 10 lead sets.
Of the two parallel windings, one has the zig-zag going up on the vector sketch and the other has the zig-zag going down. With the common neutral connection on one set of windings you can't use a double delta or conventional zig-zag to convert to single phase.

Bill
--------------------
"Why not the best?"
Jimmy Carter