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Re: Setting up a pole pig's wiring

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

Hi Phil,

This X1... does seem a little confusing. I looked at my PIG (2 ears) and the two HV outputs are labeled H1 and H2 on its nameplate. I presume they connect to the outer windings on their respective coils. The two HV coils have a common internal node (the center tap) that is not connected to the core. If one HV bushing is grounded, this common node will (presumably the inner winding of each coil) will be at 7200V. If neither HV bushing is grounded, the output will be differential like a two bushing NST. Dont know what the common node will float to, but I'm guessing zero volts if everything is balanced.

The LV side of my pig nameplate shows two coils, where each coil is internally wired in parallel for 120V operation or internally wired in series for 240V operation. All LV nodes are labled as X; not X0, X1, nor X2. My pig is wired for 240V operation where the two outer LV bushings are powered and the middle bushing is left alone. The middle bushing is, however, connected to the common node (center tap for 240 operation) between the two LV windings internally. The voltage driven onto each of the outer LV bushings are normally +120Vac and -120Vac (both hot and 180 degrees out of phase with each other). This is how 240V is delivered in the USA. Even the output of a 240V variac has both output terminals hot. In this case, one output terminal connected to the wiper sweeps from the -120Vac side to the +120Vac side to give you a 0 to 240Vac output differential. The other output terminal is common with one of the input terminals. You can NOT ground one of the LV bushings and drive 240Vac to the other unless that is what your power source is providing. I also believe the common opinion is to not ground the center LV bushing when driving the outer two bushings with +120Vac and -120Vac since the two LV coils may not be balanced.

The confusion, I believe, is mostly on the HV side and whether to ground or not ground one of the HV bushings. If someone could explain the rational for grounding one of the HV bushings using terminology such as the "inner winding of H1" and "outer winding of H1", and "inner winding of H2" and "outer winding of H2", this would help. The case of the pig (core is connected to case internally) also needs to be grounded to either mains ground or RF ground and there will be different and legitimate opinions as to which one.

Gerry R

Original poster: FIFTYGUY@xxxxxxx
In a message dated 5/1/06 12:37:55 PM Eastern Daylight Time, tesla@xxxxxxxxxx writes:

>Yes, but there is no assumption. D.C. said "as the interior side of
>primary is at X1 (grounded) potential". That indicates, connecting X1
>to ground. That is clear.

Sorry, I'm a little slow, but that still doesn't clarify it to me. If anything, this raises the additional issue of which end of the *primary* winding is adjacent to the core or secondary winding. Again, unless I'm missing some conventional labelling of pole pigs, the worst case could end up:

One end of primary (LV winding), the end furthest from core, at ground potential Other end of primary (LV winding), the end closest to core or to the secondary's (HV winding) HV end, at 240V One end of secondary (HV winding), the end furthest from core, at ground potential Other end of secondary (HV winding), the end closest to the core or to the primary's (LV winding) 240V end, at 15kV

Obviously this is the highest-stress situation, and best-case is the complete opposite. My concern is calling the "H1" or "X1" labelled ends of the windings the ones closest to the core or other winding. Is there some convention that pig manufactures must follow when labelling, or should a pig owner open and verify the connections?

>I would however clarify ground as RF ground.

    Thank you for that clarification.

>I've been running this connection on my pig ever since David
>discussed with me a few years ago.

    Glad to see it's stood the test of time!

>This is not something that can be done with an NST system where the
>hv winding is center-tap grounded. But, with a depotted NST, the
>center-tap to ground connection can then be removed and run the same
>way to minimize pri to sec stress.

On an (9, 12, or 15kV) NST, the interior ends of both HV windings are both grounded to the core. Grounding one "bushing end" puts 4.5, 6, or 7.5kV stress at the center of the HV windings to core, where there was zero stress before. If the depotted NST HV winding fails, and the core isn't still grounded, that puts the core floating at 4.5 - 7.5kV where it normally would be at ground. And thus it would put an abnormal stress to the primary winding adjacent to the core. So in that respect I don't think that connection scheme minimizes primary to secondary stress.

-Phil LaBudde
-Phil LaBudde