Cap - Puncture Voltage

From: 	Barton B. Anderson[SMTP:mopar-at-mn.uswest-dot-net]
Sent: 	Monday, December 01, 1997 9:04 PM
To: 	Tesla List
Subject: 	Cap - Puncture Voltage

Hi everyone,
I'm trying to design polyethylene caps and am running the numbers for
both rolled and flat plate caps. Both have their good and bad
characteristics/variables. In the course of running the numbers, I see
it is necessary to rely on a "real" value for puncture voltage.

I have seen info around that vary's polyethylene puncture voltage from
240/mil to 1200/mil. All I can say is "WOW", what a variance! I assume
these to be DC ratings and therefore this would need to be derated for
AC and especially Tesla Coil use. I have found a local supplier that has
30mil 4' x 8' sheets at $13/sheet. What is a "real" assumption I can use
for puncture voltage? What do you guys use? I know need to over-engineer
the cap, but going overboard can really screw up the numbers and my
wallet. It's been stated that a .090 thickness (from a few thin layers
or just one thick one) can withstand 15,000V. If this is true, then were
talking 167V/mil as a puncture voltage. I would assume this has been
derated for AC use? Anyone have a good guess at what I should use for a
puncture voltage on a per mil basis?