Transformer bank for 120v phase to phase
Transformer bank for 120v phase to phase
(OP)
Is there a way I can bank transformers for wye-wye 3phase service with 120V phase to phase? This is for a special application.
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Transformer bank for 120v phase to phase
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RE: Transformer bank for 120v phase to phase
Can you give a better idea of why you want to do this? Can you give a better idea of the types of equipment you want to run? Are you planning to bond the center point of the secondary, or one of the phases?
My gut feeling is that you really really really don't want to do this.
RE: Transformer bank for 120v phase to phase
RE: Transformer bank for 120v phase to phase
This method could also use standard single phase transformers. Your circuit breakers would still need to be rated for use on corner grounded or ungrounded 240 volt systems.
In the 400 Hertz world there is such a thing as 120 volts delta and 120Y208 volts.
Mike Cole, mc5w@earthlink.net
RE: Transformer bank for 120v phase to phase
Yes, it is possible. Two ways to obtain secondary voltage close to 120V phase-to-phase is as follow:
1-Order special three-phase transformer with 120 V in the secondary.
2- Use standard transformer with taps rated for twice the primary voltage. Operate the transformer connected to a primary voltage half the transformer rating. Automatically the secondary voltage will be half.
For example, if a secondary delta connection is allowed, choose a transformer with rated for 240 V phase to phase. The resultant voltage will be around 120V phase-to-phase.
If a YG is require the secondary voltage will be 104 V. In this case, the transformer tap should be increased as high as possible to obtaing a sec voltage closes to 120 V
RE: Transformer bank for 120v phase to phase
RE: Transformer bank for 120v phase to phase
Although an inefficient use of transformer capacity, a short-run solution may be three 480:120V transformers configured grounded-wye—grounded-wye on a 480Y/277V source—yielding 120Y/69V on the secondaries. Acceptable load on transformer bank would be ~58% of the nameplate sum of transformer-kVA ratings.
RE: Transformer bank for 120v phase to phase
RE: Transformer bank for 120v phase to phase
The local utility used to use delta connections exclusively (way back when), but the system was subsequently converted to 4-wire wye system. They still have several old transformers in the storeyard (don't ask me why) that used to be connected phase-to-phase on the primary side and delivered 120V at the secondary. If these units were connected line-to-ground, they would be underexcited and deliver 69V nominal at the secondary, which could then be banked to create 69/120V 4-wire.
You could ask your local utility if they have such a thing available in thier 'boneyard'.