Re: Single-bushing 14.7kV pigs. Thoughts?

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Original poster: "Crow Leader" <tesla-at-lists.symmetric-dot-net> 

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Monday, February 09, 2004 9:03 AM
Subject: RE: Single-bushing 14.7kV pigs. Thoughts?


 > Original poster: "Paul Marshall" <klugmann-at-hotmail-dot-com>
 >
 > The only down side is that you have a 14.7kV potential to ground. On a two
 > bushing pig, if you happen to contact one live bushing you'll live to tell
 > the tale. On a single bushing pig accidental contact with that bushing and
 > we will all be reading about you in the obituary column of the local
 > newspaper...

This seems like false safety. I measured the capacitance of my 10kVA
transformer, from the case ground to the HV terminals (both shorted). I read
1.14nF. This would come from interwinding capacitance and maybe the giant
porcelain terminals.

That's an impedance of around 1.4kohms at 100kHz and 2.3Mohms at 60Hz. You
woun't want to touch any terminal with such a low effective impedance to
ground. I once got a hell of a shock off one terminal of a cap that was
"floating" and charged to 8kV. There's nothing "floating" about these things
at AC voltages, even DC half the time. For fun last night, I connected a
frequency generator and high impedance voltmeter to the transformer I was
testing, and swept from 50 to 500kHz. The transformer is definetly a giant
capacitor, and conducts quite well between the windings.

KEN