In a message dated 3/15/2010 6:42:36 P.M. Eastern Daylight Time,
TexasRF@aol.com writes:
Teflon is rated for 1500 kv per inch. .040 thickness is good for 60,000
volts!
You can find the info at google "teflon voltage".
A typical application is for a plate bypass at VHF or UHF where 5 to 10
mil material holds off 4 KV.
73,
Gerald K5GW
Hi ,
There are different grades of PTFE. Standard PTFE is rated for only
500 volts/mil and that
is only for the first 2 or 3 mils thickness. When you increase the
thickness of PTFE to 20 mils or
more the ratings could go down to 300 volts/mil or even less. So a 20 mil
thickness of PTFE may have
a breakdown rating of 6KV or less. There are special grades of modified
Teflon out there but any Teflon
you might buy in the regular market I would consider standard Teflon.
You also have to take into account irregularities in the Teflon
sheet like pinholes, air bubbles,
etc. Also is the 5KV RF voltage RMS or peak? The peak voltage could be far
higher.
So to be on the safe side I would
derate standard Teflon to 200 volts/mil and give a generous safety factor
for the
voltage rating needed when using a thickness over 20 mils.
I would only trust a 40 mils thickness of Teflon to handle 6KV without
any surprises. To be on the really safe side I would increase that to 60 or
80 mils thickness.
There are builders of transmitting loop antennas who thought they
had enough thickness
of Teflon in their home-made tuning capacitors only to have them flash
over.
73 Todd WD4NGG
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