Re: Secondary coatings

To: tesla-at-grendel.objinc-dot-com
Subject: Re: Secondary coatings
From: Steve_Crawshaw_at_erith6-at-smtpgwy.supertension-dot-com
Date: Fri, 29 Sep 95 09:55:52 GMT
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     I've just intercepted RQ's request for info on secondary coatings, and 
     I thought I'd throw my info in here. In UK there is a component 
     distributor called RS Components who supply all sorts of electronics 
     gear. They have a number of products for HV insulation. I have got 
     hold of a tin of the following
     
     Anti Corona Lacquer 569-290    $2.86 400ml Aerosol
     
     This has a dielectric strength of 48Kv/mm with a working temp of up to 
     150 degrees C. I intend to follow RQ's preparation and sealing method 
     for secondary construction on a 4.5 inch Diameter Perspex (Lexan) 
     former, but use this stuff instead of polyurethane.
     
       Unfortunately the perspex has been extruded, not moulded, so there 
     are small striations / lines running along the length of the tube. 
     This is why I intend to wet & dry it before winding. Also being 
     extruded, it is not completely round :( I have some 0.4 mm enammeled 
     Cu winding wire and I have calculated 1150 turns with a 4:1 aspect 
     ratio. On top of this goes my 12" x 3.5" stainless steel toroid. I 
     have just had this shotblasted and it is double sexy. I have silver 
     soldered a 1/16" thick circular steel plate into the centre of this to 
     support the toroid while on top of the coil. I have asked this before, 
     but I can't remember if I got an answer. When constructing the 
     secondary coil, I seem to recall that RQ recommends sealing end caps 
     on the former. Why is this?
     
     Anyway, back to the point in question. There are some more products of 
     interest in the same section of the RS book:
     
     
     modified silicone conformal coating
     90Kv/mm dielectric strength
     red and transparent colours
     fluoresces under UV (good for tracing corona leakage?)
     temperature -70 - 200C
     
     best cure 24 hours -at- 100C
     
     200ml aerosol 494-714 $6.20
     
     
     Tropicalised varnish
     
     Acrylic varnish with UV tracer
     touch dry in 10 mins
     recommended drying 24 hours -at- 21C + 4 hours -at- 60C
     temp -60 - 130C
     dielectric constant 2-45 -at- 10KHz -at- 21C
     dissipation factor 0.028 -at- 10kHz -at- 21C
     
     500ml tin 188-627 $6.29
     
     Hope this info is of use. As I say this is a UK source but no doubt 
     there are equivalents in USA. Prices are in pounds sterling but I 
     can't make my keyboard do Pound signs. Cultural imperialism or what?
     
     
     Later
     
     Steve
     
     
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