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Re: [TCML] Terry Filter for a pig?
If the transformer is designed to be wye-connected, this seems like the way to go. However it appears that some older units as well as some of the very-HV units are not meant to be wye-connected, as this places different requirements on the insulation. I have a GE JVT-200 200:1 two-bushing PT (24kV) that the documentation expressly forbids you to connect wye unless you derate the voltage significantly. One of my pole pigs, a two-bushing 34.5kV unit, has only a delta rating. In such cases as these, it may be more appropriate to use a filter similar to what Terry used to prove the original concept. That is, simply place a doorknob cap directly across the PT or pig, then two big resistors between transformer and load (i.e., no ground anywhere). This seemed to work quite well, according to Terry's data. Of course, follow this with a safety gap in an RSG scenario!
If your pole pig is of the single-bushing sort or else has a "Y" rating, then the endpoint-grounded primary wiring scheme you're talking about does seem like the cool thing to do.
Cheers,
Aaron, N7OE
--- On Tue, 9/2/08, Lau, Gary <Gary.Lau@xxxxxx> wrote:
> From: Lau, Gary <Gary.Lau@xxxxxx>
> Subject: [TCML] Terry Filter for a pig?
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Date: Tuesday, September 2, 2008, 1:11 PM
> Changing the subject line...
>
> Terry filters are usually used for NST's with mid-point
> grounded secondary coils, and this is why there are
> basically two of everything - one filter for each side. But
> with a pole pig, wouldn't you tie one of the HV bushings
> to RF ground? I'm not sure why there needs to be two
> complete filters (as shown in the photo link) as with
> NST's.
>
> Regards, Gary Lau
> MA, USA
>
> > -----Original Message-----
> > From: tesla-bounces@xxxxxxxxxx
> [mailto:tesla-bounces@xxxxxxxxxx] On
> > Behalf Of bartb
> > Sent: Tuesday, August 26, 2008 8:25 PM
> > To: Tesla Coil Mailing List
> > Subject: Re: [TCML] Terry Filter Caps
> >
> > Hi Phil,
> >
> > Yes, I thought Adam has sent the post (had two lines
> of "so and so
> > wrote:" and for some reason thought it was Adam).
> >
> > Anyway, wow, a Terry filter fitted for a pig!
> >
> http://members.aol.com/fiftyguy/TC_Pig_Terry_Filter.jpg
> >
> > I especially like the horn gap approach and even the
> sphere's on the
> > ears! It certainly doesn't hurt to provide a
> little transformer filtering.
> >
> > Take care,
> > Bart
> >
> > FIFTYGUY@xxxxxxx wrote:
> > > Yeah, and the MOV's are slow to respond to
> transients at 1 MHz. But they
> > > certainly are nice to have!
> > > Some distribution arrestors use
> "combined technology" with a spark gap
> > > in series with the MOV element, just to
> complicate things. I think the big one
> > > I've got sitting around is like that, since
> the last time I tried it across
> > > my pig on an untuned coil, hot metal sparks
> actually shot out of it and
> > > rolled on the ground.... The two arrestors on my
> pig have done just fine at
> > > 15+kVA, even when the safety gap has been firing.
> I feel I've got that safety gap
> > > set pretty tight, but my arrestors are as tight
> on the MCOV specs as I dare go
> > > (even tighter than the specs for the "usual
> NST" Terry Filter).
> > >
> > > -Phil LaBudde
> > > Center for the Advanced Study of Ballistic
> Improbabilities
>
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