On Tue, 25 Aug 2009 00:26:17 -0700, ngdbud wrote:

> I'm working on building a high voltage capacitor. I have heard that PET
> has a very high voltage breakdown. I came across an excellent source of
> PETG (Polyethylene Terphthalate Glycol). How much will this affect the
> puncture resistance? I did a bench test that went alright for being in
> open air. I'm confident it will handle the voltage I need, but I'd still
> like some solid numbers. Couldn't find any with a google search.

There are so many variables that can affect this.  Cleanliness, how 
oversize you make the dielectric, and the dress of the edges of the 
plates immediately springs to my mind; I'm sure there are many more that 
I'm not aware of.

I'd do a hipot test before I put anything into service, and I'd consider 
doing it regularly if it mattered.

-- 
http://www.wescottdesign.com

Bert Hickman wrote:
> ngdbud wrote:
>> I'm working on building a high voltage capacitor. I have heard that
>> PET has a very high voltage breakdown. I came across an excellent
>> source of PETG (Polyethylene Terphthalate Glycol). How much will this
>> affect the puncture resistance? I did a bench test that went alright
>> for being in open air. I'm confident it will handle the voltage I
>> need, but I'd still like some solid numbers. Couldn't find any with a
>> google search.
> 
> Two vendors claim 16 kV/mm. Should be OK for DC and low frequency AC 
> applications. May need to oil immerse to prevent corona damage 
> especially around the capacitor plate boundaries.
> 
> http://www.matweb.com/search/DataSheet.aspx?MatGUID=4f94ed265e2e4a5b8edfbf3d82a778b3 
> 
> http://www.matweb.com/search/DataSheet.aspx?MatGUID=0ae8a31119d6490cb52259ccbdf15664 
> 
> 
> Bert


Some additional info:
Other suppliers quote a lower value (410 V/mil or ~10.4 kV/mm) for Vivak 
PETG sheet:

http://toronto.lairdplastics.com/content/view/335
http://www.happcontrols.com/msds_sheets/96-0915-00.pdf

So, YMMV.

Using two or more thinner sheets will have a much higher standoff 
voltage than a single sheet of the same total thickness.

ngdbud wrote:
> I'm working on building a high voltage capacitor. I have heard that
> PET has a very high voltage breakdown. I came across an excellent
> source of PETG (Polyethylene Terphthalate Glycol). How much will this
> affect the puncture resistance? I did a bench test that went alright
> for being in open air. I'm confident it will handle the voltage I
> need, but I'd still like some solid numbers. Couldn't find any with a
> google search.

Two vendors claim 16 kV/mm. Should be OK for DC and low frequency AC 
applications. May need to oil immerse to prevent corona damage 
especially around the capacitor plate boundaries.

http://www.matweb.com/search/DataSheet.aspx?MatGUID=4f94ed265e2e4a5b8edfbf3d82a778b3
http://www.matweb.com/search/DataSheet.aspx?MatGUID=0ae8a31119d6490cb52259ccbdf15664

Bert
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I'm working on building a high voltage capacitor. I have heard that
PET has a very high voltage breakdown. I came across an excellent
source of PETG (Polyethylene Terphthalate Glycol). How much will this
affect the puncture resistance? I did a bench test that went alright
for being in open air. I'm confident it will handle the voltage I
need, but I'd still like some solid numbers. Couldn't find any with a
google search.