HV Transformer insulation

[KC9LKE]

I have rewound several low to medium voltage transformers with good results in the past and would like to rewind a transformer for use as a general purpose plate supply. I am considering a 97 lb, 5 kVA that has a 220/440V primary and a 275/550V secondary.It is an EI core with the secondary over the primary. Being 5 kVa gives a comfortable winding window to work in and the transformer is in good condition. Also on hand, is 20 lbs of Dodge #22 heavy soldereze, a vacuum chamber for the potting, and a lathe for the winding.

The goal is to rewind the secondary for 3200 Vrms at 1 Amp, continuous. I will also add a grounded shield between the primary and secondary. To keep the post short I omitted the calculations, but can supply if needed.
 
When I worked for a shop that built transformers and chokes we only used Mylar no questions asked. For low voltage applications at home I was able to go the budget route and use fish paper that I had on hand and polyurethane for potting. For this project I want to use proper, better, insulating materials and do a FB job of it. I am considering Nomex or Mylar for insulation and possibly Glyptal for potting. Before I take on the task of sorting through data sheets I would appreciate suggestions and direction from the group on typical insulating and potting materials for a HV transformer in this class.

Best Regards
Ted / KC9LKE

[WD5JKO]

Ted,

Take a look at the following web page. I hear they can sample small quantities of varnish, or whatever.

http://www.dolphs.com/index.cfm

Also, make sure the primary as it is now has enough turns for whatever line voltage you have. Could be trouble if you put 250 vac into that 220 vac primary.

Good Luck,
Jim
WD5JKO

[KC9LKE]

Jim:

Thanks for the link.
Even though I plan to use a variac with the supply. One of the first things I’ll do is slowly ramp up the primary voltage while monitoring the current, looking for nonlinearity, and record the voltage. Hopefully it’s below our service voltage.

Thanks again.

Ted / KC9LKE

[WA1GFZ]

I like 3 mil Kapton for high voltage. 7,000 volts/mil