High Voltage insulating resin

[xzswq21]

Hello
I want to use a high voltage insulating resin for several high voltage transformers (10kV and 20kV and above) but I don't how I should choose a proper resin:






Thanks

[David Hess]

Wax may be an easier to use alternative.  There are specific was formulations intended for potting.

[TimFox]

With any potting material, be careful to eliminate bubbles from the final state.  Normally, this is done by pumping a vacuum above the "pot" while the material is still liquid.
Wax is a traditional material:  note that it shrinks drastically at the phase transition between liquid and solid as it cools.

[T3sl4co1l]

Beats me.  Have you checked mfg websites (e.g. 3M)?

As I recall, the stuff used in FBTs is extremely hard; probably mineral filled (silica or otherwise?).

And yeah, you definitely want a vacuum pot for that.  You can verify quality in a couple ways, like hi-pot for isolation barriers, but also partial discharge for breakdown around windings -- a pocket of air exhibiting breakdown, is detectable as high frequency (impulsive) emissions, when the part is excited (preferably by a nice smooth sine wave).

Tim

[David Hess]

One reason I would avoid random epoxy potting compounds is that some have horrible dielectric loss even without leakage.  Tektronix had a horrible time with this when they initially changed from wax to epoxy.

Wax is a traditional material:  note that it shrinks drastically at the phase transition between liquid and solid as it cools.

That is why I mentioned that there are specific wax mixtures used for potting.

[HighVoltage]

Huntsman and LORD are two companies that produce very high quality 2 component resin for high voltage insulation.

As others have mentioned, for a good high voltage insulation, you need to pot under vacuum.
One important reason for the vacuum is to get all humidity out of the system before potting, otherwise the humidity can be a big factor in the insulation properties.

[TimFox]

A fundamental reason to avoid bubbles is a not-obvious electrostatic result.  In a parallel-plate geometry, the E field between the plates with a uniform dielectric (or vacuum) is E = V/x, where x is the spacing.  If almost all of the gap is filled with a dielectric with constant k, but a thin layer of air (k = 1) occupies a small region, the equilibrium value of the field in the dielectric is unchanged, but the field in the air gap is increased by the factor k, which is bad since the breakdown field in air is probably less than that of the dielectric.

[xzswq21]

With any potting material, be careful to eliminate bubbles from the final state.  Normally, this is done by pumping a vacuum above the "pot" while the material is still liquid.
Wax is a traditional material:  note that it shrinks drastically at the phase transition between liquid and solid as it cools.

As others have mentioned, for a good high voltage insulation, you need to pot under vacuum.
One important reason for the vacuum is to get all humidity out of the system before potting, otherwise the humidity can be a big factor in the insulation properties.

I want to see some videos about it, I want to build a simple one in my room! I'm alive with my instruments!

[xzswq21]

One reason I would avoid random epoxy potting compounds is that some have horrible dielectric loss even without leakage.  Tektronix had a horrible time with this when they initially changed from wax to epoxy.

Wax is a traditional material:  note that it shrinks drastically at the phase transition between liquid and solid as it cools.

That is why I mentioned that there are specific wax mixtures used for potting.

could you please show me a good wax and a mixer?
I found an epoxy with the below specification:

Dielectric coefficient= 4.6
Viscosity= 1080 Centipoise
Density= 1.47 gr/cm3
Pressure resistance= 742 kgf/cm2
Volume resistivity= 5e14 Ohm.cm3
Surface resistivity= 9.8e13 Ohm
Heat Deflection Temperature= 50 'C

is it a good insulating Epoxy?

[David Hess]

could you please show me a good wax and a mixer?

I do not know anything more than you can find online.  I know that it takes more than pure paraffin wax.

[xzswq21]

I want to buy a vaccum pump to remove air bubble in an electrical insulating resin, target pressure as you recommended me should be around 10-50mBar,
internal volume of my Vacuum oven is 0.45 cu.ft. Int or 12.7 Liters (inside chamber dimensions :8"x8"x12”)
now I have two choices for the vacuum pump:

"Fisher Maxima C plus M2C" and "Welch 8890A"

Fisher M2C:
https://www.fishersci.com/shop/products/fisher-scientific-maxima-c-italics-begin-plusitalics-end-vacuum-pump/0125777

https://beta-static.fishersci.com/content/dam/fishersci/en_US/documents/programs/scientific/brochures-and-catalogs/brochures/fisher-scientific-maxima-c-plus-vacuum-pumps-brochure.pdf

Welch 8890A-55:
https://www.idealvac.com/NEW-Welch-8890A/pp/P104262

https://www.idealvac.com/files/brochures/Welch_8890_Owners_Manual.pdf

which one is better for my application? as you see the internal volume of the oven is small.
I will buy a used one, but the Welch 8890 has an air lock system! it means:

When power to the pump is turned off, this valve closes automatically, maintaining vacuum in the system being evacuated, and vents the inside of the pump to atmospheric pressure.

Thanks

[BrokenYugo]

I highly doubt you need a $2500 scientific vacuum pump for this, a cheap AC service vacuum pump should do.

[xzswq21]

I highly doubt you need a $2500 scientific vacuum pump for this, a cheap AC service vacuum pump should do.

the price of a used  one is only $100-$200 

[David Hess]

A cheap AC service vacuum pump is more than good enough.  A regular air compressor could also be used by attaching to the intake.

[Vtile]

Shellac is one natural resin used in the past as electrical insulator.. Most probably is still used as "secret incredient" in many products. 

https://electrical-engineering-portal.com/dielectric-strength-insulator-materials

[Vtile]

Dielectric coefficient= 4.6

I don't know exactly, but should that be "Dielectric constant"? If not, what is the difference?

[BrokenYugo]

I highly doubt you need a $2500 scientific vacuum pump for this, a cheap AC service vacuum pump should do.

the price of a used  one is only $100-$200 

I would assume they're cheap used because they have who knows how many hours on them (as I recall, rebuild parts for most brands are expensive or outright never offered) with who knows what sucked through them, probably by careless students*. I'd take a new Chinesium pump over that, e.g. (assuming USA) $150 Harbor Freight 2 stage 3CFM 22.5 micron, or $90 for single stage 2.5CFM 75 micron, even if they're an order of magnitude off spec that's still sub millibar.

*Which is probably why they're asking $2500 for what look a whole lot like a $200 AC service pump with a different hardware kit, schools will just pay it.

[xzswq21]

Dielectric coefficient= 4.6

I don't know exactly, but should that be "Dielectric constant"? If not, what is the difference?

Yes, it's dielectric constant.
what do you think about "3M™ Scotchcast™ Electrical Resin 8N"
https://www.3m.com/3M/en_US/p/d/b5005042037/

there are a lot of electrical resin from 3M:
https://www.3m.com/3M/en_US/p/c/coatings/electrical-resins/

is it a good epoxy resin for high voltage transformer potting?

[HighVoltage]

No, this 3M product would not work !

It is meant to be applied to motor windings at the end of the winding process.
But not for high voltage insulation.

[xzswq21]

No, this 3M product would not work !

It is meant to be applied to motor windings at the end of the winding process.
But not for high voltage insulation.

I checked most of 3M epoxy resin datasheets but I couldn't find any high voltage characteristic in any of them, actually most of them have 300-400V/mils electrical strength, please help me to find an epoxy resin, some of them are Room temperature curing and some of them are heat curing.

[geggi1]

I have used 3M and Loctite products for repair and installation of HV transformers and terminations.
E every time i have dont these kinds of job i have got a repair procedure form the manufacturer of the equipment or contacted the support line/email at 3M or Loctite. The support line will give you an recommendation for the best product or products  to use .