Re: [TCML] Pig, Can a dual bushing be ref'd to gnd?

["J. Aaron Holmes" <jaholmes@xxxxxxxxxxxxxxxxxx>]

> From: ConorPerry@xxxxxxxxxxx <ConorPerry@xxxxxxxxxxx>
>
> With a dual HV bushing pole pig, can
> one HV leg be tied to ground?  Are the HV windings
> completely arbitrary/isolated from the LV side?

It is *probably* safe to do this with your pig, but the voltage rating on the nameplate will provide important clues.  What exactly does it say?

If the rating is something like "14400/24940Y" or "7200/12470Y" ("Y" may also be "GRDY" or "GNDY" or something similar) then you're safe; the transformer is designed with such a configuration in mind.  If, on the other hand, the rating is simply "14400" or "7200" or similar (occasionally with a "D" on the end), I would assume that it is *not* safe until I heard otherwise from the manufacturer (or read otherwise in the manual).

I have several transformers in both categories, and, in the case of my PT that's rated "24000," the manual clearly states that a grounded Y configuration is *not* supported without significantly derating the high voltage (and it provides the derated value).  Ratings like this (i.e., without the "Y") seem to be more common in the higher voltages, but I've seen units with ratings like "13800 D" and "14400" before, too.  You do not ground one bushing of such units without risking ruining them.

In short:  Check the rating.  You're probably ok, but don't assume anything.

Cheers,
Aaron, N7OE
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