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Re: 12740Y/7200



Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi David,

When a two bushing single phase PIG is marked 7200/12470Y, are the two bushings suppose to be connected across two of the three phases and subsequently see 12470 across the two bushings, or are the two bushings suppose to be connected from one phase to neutral and thus see only 7200V?? If the former connection is allowed, it would seem like there would be a common mode voltage on the two bushings and this would be a problem. If only the latter connection is allowed, then why two HV bushings??

Also, does the latter connection result in 120/240 on the LV side, and if so then would the 12470V connection result in 208/416 on the LV side??

(just when I thought I understood it)

Gerry R.


Original poster: David Dean <deano@xxxxxxxxxxxxxxxx>

It means The primary voltage is 7200 phase to ground, 12470 phase to phase.
All single phase pole mount transformers are connected Y to Y in 3 phase, If a
pad mount 3 phase TRANSFORMER IT WILL BE Connected Delta to Y. In single
phase all power distribution transformers are connected   from one phase
primary to one phase secondary. All pole pigs rated 12470Y/7200 Are connected
to a single 7200V line. Only 3 phase transformers are connected 12470 Delta
on the primary side, and all of them that I have seen in the real world are
Pad Mount. Of the possible ways transformers can be connected there are Y -
Y, Delta Delta, Y delta. Y - Y is a no no for a three phase transformer. Any
imbalance in currents will result in neutral currents that will destroy the
transformer. Using three single phase transformers in Y - Y is OK because the
cores are not connected and the neutral of the secondary can be connected to
the neutral of the primary and no neutral current will flow if there is an
imbalance.

Anyway that is the theory.
later

deano