proper wire feedthrough sealing of HV oil filled container?

[Jim Horton]

So I decided to use mineral oil once again for my HV transformer device
after debating and even trying paraffin. However, this time I want to
be sure my wires passing through the PVC junction box are sealed
correctly so no oil leaks through.

The transformers will be inside a 6x6x6 PVC junction box (which takes up
about 50% less volume than the prior box I used) and four connections
will be needed:

2 low voltage 600 V wires for driving the transformers, and
2 wires for high voltage output (around 100 KVDC)

So, these four wires will need to pass through the PVC box into the oil
and to the transformers.

In the past, I used two part epoxy to seal the solid wires on the inside
of the box with generous application of silicone around the wire outputs
on the outside of the box (I added the silicone layers because the
outside wire didn't quite have enough insulation and sparks would jump
to my hand sometimes... a bunch of layers of silicone around the exit
points stopped this).

Wires are all thin 20 gauge solid. I was going to use the same
procedure, using the epoxy to seal around the inside of the container
where the wire feedthroughs occur with silicone layers on the outside,
but maybe there's a better way? As I said before, when all is dry, the
interior will be filled once again with mineral oil. The entire volume
of the container will be filled with oil, so all holes with wires
passing through will need sealed correctly. Thanks in advance for your
ideas.

 

[Jim Horton]

Since a picture says a thousands words, here is what I had and now what
I want to do. I have included captions describing what you are seeing
with the last indicating my uncertainty about proper HV feedthrough set up:

https://imgur.com/a/15c4FKK

Comments and suggestions welcome. Thank you.

 

[Rheilly Phoull]

On 21/10/2019 2:36 am, Jim Horton wrote:

Since a picture says a thousands words, here is what I had and now what
I want to do.  I have included captions describing what you are seeing
with the last indicating my uncertainty about proper HV feedthrough set up:

https://imgur.com/a/15c4FKK

Comments and suggestions welcome.  Thank you.

Can you bring all wires out through the top cover ?

Should make sealing with the silicone a bit better.

 

[pfjw@aol.com]

Some issues to consider:

a) Mineral oil has a coefficient of thermal expansion approximately 4x that of water. Meaning you *must* provide for this in your design. If not, you will get leaks, later if not sooner.
b) Some RTV silicon materials release acetic acid in the vulcanizing process. Endeavor to get materials that are compatible with electrical components.
c) Better yet, use an electronic epoxy. There are materials that bond very well to PVC/CPVC, and remain flexible when cured.
d) Mineral oils used for insulation must be sealed - not exposed to air or oxygen, and, most especially not Ozone - which you are producing in considerable volume (sparks).
e) Which also applies to some RTV materials - which is why, in general, they are not favored in electronic applications.

Good luck with it! And make sure your neighbors don't understand that such a large arc will step on any rF devices for hundreds of feet... if you are not careful.

Peter Wieck
Melrose Park, PA