Insulating a 10 kV solder connection - Page 1
Forum section: electronics / projects

author: trubetz
author_rank: Newbie
timestamp: November 20, 2024, 08:44:44 am
content: Greetings everybodyI have a task of permanently connecting two wires (20 AWG in rubber insulation 4 mm in diameter) that operate at a voltage of up to 10 kilovolt. The question is: how do I insulate the solder joint? The heat shrink tubes that I have at hand have a voltage rating of 600 volt, so these are clearly not enough. I think there must be an industrially correct way of doing this, but I do not know how to find this either. Please advice.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 20, 2024, 08:51:26 am
content: You need to exclude all air to prevent corona - probably need to use a sleeve filled with something like silicone

author: Gyro
author_rank: Super Contributor
timestamp: November 20, 2024, 09:25:29 am
content: I hope this isn't a high energy situation!Assuming low current cabability, I've found that multiple layers of 3:1 ratio adhesive lined heatshrink work well - the smallest sized to be a close fit on the rubber insulation before shrinking, to exclude air as Mike says.

author: trubetz
author_rank: Newbie
timestamp: November 20, 2024, 09:37:36 am
content: Quote from: Gyro on November 20, 2024, 09:25:29 amAbsolutely not, we are talking about a power supply that has a short circuit protection at about 100 uJ energywise.Speaking of the layers, how "multiple" are we talking about? Obviously I cannot stack 5+

author: Psi
author_rank: Super Contributor
timestamp: November 20, 2024, 09:42:37 am
content: If it was me, I would use some electronic rated silicone RTV to bridge the gap all around the solder join and increase the diameter to match the insulation.Once that cures I would heatshrink over the join using the kind of heatshrink that comes with built-in glue inside.But it wont be able to handle much bending stress, if any.

author: Someone
author_rank: Super Contributor
timestamp: November 20, 2024, 11:11:15 am
content: Starting with some heat shrink that specifies a minimum wall thickness and significant dielectric strength (such as XPLO) is only half the battle, that gets the voltage rating in theory but controlling the fields (avoiding voids!) is an art in its self. The cable supplier should have some suggestions.

author: Ian.M
author_rank: Super Contributor
timestamp: November 20, 2024, 01:04:07 pm
content: It may be preferable to do a rigid potted joint, as getting all the bubbles out is easier if you can de-gas pourable resin in a vacuum chamber vs trying to apply silicone sealant without trapping any air.

author: nfmax
author_rank: Super Contributor
timestamp: November 20, 2024, 02:45:15 pm
content: Possibly paraffin wax? If you can fully immerse the joint into melted wax and allow time for it to fully soak in. You may need a protective mechanical layer as well, though.

author: robert.rozee
author_rank: Frequent Contributor
timestamp: November 20, 2024, 03:57:40 pm
content: Quote from: trubetz on November 20, 2024, 08:44:44 ama. is it practical to just replace the two wires with a single (longer) wire?b. if a single wire is not possible, can you use a plug and socket rated at 10kv?cheers,rob :-)

author: TimFox
author_rank: Super Contributor
timestamp: November 20, 2024, 04:21:35 pm
content: If you must solder the two wires together, be sure there are no sharp edges or points sticking out, where the local electric field will be far above the average value.Can you solder them into a copper sleeve before wrapping them in appropriate insulating tape or heat-shrink?The 600 V rating on your heat shrink assumes that two conductors are separated by the tubing wall, with 600 V difference between them.It's the same way insulation ratings for normal wire are specified.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: November 20, 2024, 04:56:57 pm
content: A short search:https://html.duckduckgo.com/html?q=high+voltage+heat+shrinkquickly finds:https://www.mcmaster.com/products/high-voltage-heat-shrinks/which claim to have heat shrink up to 5kVac, so 2 layers should suffice.Another tip I saw in a 3M datasheet: With the glue filled types, start crimping them from the center, and then slowly moves outwards, to reduce the chance of air bubbles.Another option is to have a look at how high voltage cables are coupled, and use the same materials. It looks like they use the self-vulcanizing rubber tape instead of heat shrink. Topping that off with a layer of heat shrink may be a good idea too. The high voltage power cable splices are built up from multiple layers.I also don't understand where the "600V" rating for "regular" heat shrink comes from. Nearly all plastics have dielectric strengths of 10kV to 40kV per mm. the 600V rating is very likely just a waiver so they are not responsible, can get away with less stringent quality control and can therefore put the stuff on the market for a lower price.

author: TimFox
author_rank: Super Contributor
timestamp: November 20, 2024, 05:45:42 pm
content: For really high voltage cables (100 kV), we used a special high-dielectric constant (and somewhat conductive) tape around the conductor, with an EPR self-fusing rubber tape over that, and finished with a self-fusing silicone rubber tape.With self-fusing tapes, one applies them "half-lapped" and the layers adhere to each other.When we started using the high-dielectric constant tape (in grad school), the technician helping me and I both wondered about the other guy, since the tape smelled like dirty tee shirts and we each thought the other bathed normally.

author: Psi
author_rank: Super Contributor
timestamp: November 22, 2024, 12:14:26 pm
content: Quote from: TimFox on November 20, 2024, 05:45:42 pmSelf-fusing tape is a great idea for high voltage.It's not an idea i had considered, but it makes a lot of sense.

author: Zoli
author_rank: Frequent Contributor
timestamp: November 23, 2024, 08:01:22 am
content: Quote from: Psi on November 22, 2024, 12:14:26 pm3M 70 is a tape I worked(for high(~150oC) temperature ); it has a 34kV/mm specified dielectric strength.

author: CosteC
author_rank: Regular Contributor
timestamp: November 25, 2024, 08:32:08 pm
content: 10 kV is relatively lowone layer of tape use for transformers usually withstands 5 kV, so 3-4 layers makes sensible insulation.Main challenge is to make it in even, overlapping layers, without trapped air.Heatshrink tubes with glue shall work well too. Standard heatshrink tubes have withstand of 10-20 kV/mm.Silicon tubes can work in higher temperatures but are not so conveniently adjustable in size/diameter.IPC-A-610/620 recommends smooth, round soldering joints. Spikes are not acceptable as cause high field gradient as well as can damage insulation mechanically.