How to insulate 50kV cable joint - Page 1
Forum section: electronics / projects

author: Riotpack
author_rank: Regular Contributor
timestamp: February 25, 2015, 12:50:04 pm
content: Hi,I purchased a MH100/503 0-50kV 100w power supply. When I received the supply, the ebay seller had cut the HV lead around 50mm from the unit. The HV lead is not removable and leads to the potted HV section of the supply.When I run the supply I get corona noise and the supply arcs over to the chassis. I need to join a new piece of HV cable to the short lead coming from the unit.What is the best potting compound to use for this? Or is there any other method to connect this cable??Thank you for your expertise.

author: alho
author_rank: Contributor
timestamp: February 25, 2015, 01:40:30 pm
content: My DIY solution would be...Attach longer cable (solder, crimp???). Slide thick walled plastic/silicone tube that is very tight fit over the joint. Maybe add oil or glue to prevent creepage between tube and cable.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 25, 2015, 02:17:48 pm
content: It may not be professional and up to official specs, but I have had great results with multiple layers of heat shring tubing, the type that incorporates hot melt glue. I went up to 30 kV and had just three layers. The important aspect of insulating HV stuff is to displace air as well as possible; otherwise, corona discharge happens inside the insulation, consuming power and slowly degrading the plastic.I have also used neutral-curing silicone to insulate 34 kV CRT connections, but the silicone type is very important, as I found out with trial and error...

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: February 25, 2015, 02:52:16 pm
content: The key thing is to keep air out, and not open up gaps during flexing. A soft compound like a 2-part silicone is probably theoptimum - I don't know how well 1-part silicone cures in an enclosed space - maybe do a test piece & cut it open to see how well it cures.

author: LaserSteve
author_rank: Super Contributor
timestamp: February 25, 2015, 03:27:06 pm
content: I work in a HV oriented laser lab. My technique for small diameter slim joints with no leakage current is as follows.Step one, Solder joint with no sharp points after soldering. File and or sand the junction if need be.Step two, A few layers of Wrap with Teflon plumbing tape so that no metal is showing. This wrap should be a fraction of a millimeter thick.Step Three, Thin layer of ceramic loaded epoxy, Hysol C1 White. If you do not have access to C1, a high grade clear epoxy may be used. Allow epoxy to set. HV cable inner wire is mechanically weak. So the joint must be epoxy reinforced.Step Four, another layer of Teflon Tape. This time going out over the insulation for 5 mm, and having a thin layer of wet epoxy under it.Step five, A Dressy, smooth layer of the epoxy. C1 may be smoothed by brief application of a heat gun. The amount of heat needs some practice so you do not greatly accelerate the cure.Step Six, Heat Shrink tubing of the kind with glue inside. One small piece over the junction, One larger piece to add strength and make this joint look good. It helps if the outer layer color matches the cable color.If I'm worried about the cable needing to flex, I add more thin layers of epoxy and tape, then do the dressy layer.Some of my joints done this way have worked for 10 years now.-------------------------------I avoid RTV type Silicon at very HV, it exhibits a high leakage current, and it degrades under ozone.3M offers a liquid electrical tape that is far better then RTV for HV work.Notes:Hysol C1 White is sort of a must have if you do lab work. It is a very low outgassing, somewhat thermally conductive, mechanically stable epoxy that can withstand high temperatures and harsh chemicals. Its loaded with MgO and Al2O3 powder. Lab guys will know it as a "Torr Seal" analog. Airplane folks will know it is as the epoxy used to bond leading edge sheet metal on the wings of fast jets.------Normally we use a high grade RG8 Teflon cored coax cable for 50-60 Kv work. You use a soldered PL259 style connector with the inner insulating portion removed. That gets soldered to the braid with 4-6" inches of the Teflon core sticking out and terminating in a male banana plug. The mating side is a PL259 panel mount with 4-6 inches of small Teflon or pcv pipe submerged in potting compound or castable plastic. At the end of the PVC is the female banana plug. The Cable braid is the ground, the inner is the HV lead. Works a treat to 85 Kv or so. At least four makers of HV power supplies consider this the standard method, which dates back to World War II.--------------------If you must find more wire, look for "TVS" wire for HV.Surprisingly 600V rated Oldaker Corp. rubber test lead wire with the slightly conductive inner insulation is very good to 20-30Kv or so. It makes for very good ground return leads for HV projects. Little known fact, the inner polymer layer of HV cable next to the wire core is slightly conductive. This is to avoid corona inside.At 25 KV and up, I start worrying about the ground return being nearly as well insulated as the HV lead.Steve

author: 3roomlab
author_rank: Frequent Contributor
timestamp: February 25, 2015, 06:22:40 pm
content: like this hysol?man i was looking for something like this and i dont know what to look forhttp://www.henkelna.com/product-search-1554.htm?nodeid=8797906075649

author: MK
author_rank: Regular Contributor
timestamp: February 25, 2015, 06:51:14 pm
content: There is also one of the self amalgamting tapes that is recommended for HV connections.

author: eneuro
author_rank: Super Contributor
timestamp: February 25, 2015, 09:11:07 pm
content: Quote from: LaserSteve on February 25, 2015, 03:27:06 pmYep, it looks like they used something based on Hysol C1 to glue temperature sensors to stainless stell for Mars missions and reveal another properties of this epoxy gluepdf: Performance of epoxy glue mounted temperature sensors for application in the ExoMars environmental chamberIs it thisLoctile Hysol 1Cwhite or something different you suggest for HV?BTW: DS18B20 -55÷125°C temperature sensor was glued

author: calexanian
author_rank: Super Contributor
timestamp: February 25, 2015, 09:19:58 pm
content: Proper fitting gland fittings into a container you can fill with Poland have sealed. That's the real way.

author: calexanian
author_rank: Super Contributor
timestamp: February 25, 2015, 09:23:15 pm
content: Proper fitting gland fittings into a container you can fill with Poland have sealed. That's the real way.

author: CM800
author_rank: Frequent Contributor
timestamp: February 25, 2015, 09:41:25 pm
content: Quote from: LaserSteve on February 25, 2015, 03:27:06 pmI'm curious, what would you recommend for 150kV X-Ray transformer cable? the kind of stuff that has a center wire, then around 1cm radius of orange rubber - silicone stuff and then a ground shield around over that then a white plastic sleeve? (I have a 70kV 20KVA XRT transformer with some wire)

author: LaserSteve
author_rank: Super Contributor
timestamp: February 26, 2015, 03:11:56 pm
content: http://www.henkelna.com/product-search-1554.htm?nodeid=8797906075649McMaster-Carr and Fastenol can order it in the states, I buy the tube kit as the shelf life is Approx 1.5 years. 8-16$ a box depending on whom you get it from and how long its sat on a shelf.As for the HV cable, I spend a year working on CT machines at 280 KV. YES! You want the Med grade HV cable at this point, with the cone shaped connectors and glands. Yes, its white pvc outer with an orange or cabon doped black core.TVS60 would work fine at 70KV, if you can connect it using Teflon insulation and air insulate it as much as possible using glass reinforced fiberglass standoffs. Usually we use 1/2" diameter fiberglass rods for that. McMaster Carr sells raw Teflon blocks and rods.Corona gets positively evil above 30Kv, so if one learns the techniques of using glass, air, Teflon, and poorly conducting polymer insulation, one can do quite well at home. The Farnsworth fusion and tesla guys have nice tutorials on their websites.50-60 Hz AC is insulated a bit differently then the HV tesla stuff.BE CAREFUL, HV AC AND DC IS VERY DANGEROUS> WATCH OUT FOR MAKING ACCIDENTAL CAPACITORS AT HV DC< SUCH AS CHARGING 20 FEET OF COAX WITH HV DC. LARGE AMOUNTS OF GROUNDED STRUCTURES ARE ADVISABLE!.After all, advice on the internet is often worth less then the recycled electric fields its carried on. (Hint, Electrons don't really move much in cables!)Steve

author: calzap
author_rank: Frequent Contributor
timestamp: February 26, 2015, 04:22:11 pm
content: Be careful with induction too. Doesn't take much of a coil, or even a straight length, of wire near 50 KV to transfer a lot of voltage. Some linemen have experienced this the hard way. Even with DC, changes (like start-up and shut-down) in voltage can induce a spike. Even if it's shielded coax, a break or disconnect involving the shield can let the bad waves out.50 KV limited to 100 W is 2 mA. It would be unpleasant and might harm you, especially if you have a pacemaker. 500 V at 100 W is 200 mA, lethal territory.Mike in California

author: calexanian
author_rank: Super Contributor
timestamp: February 26, 2015, 08:37:30 pm
content: How the heck did predictive text get Poland from Oil in my last post, and why did it post twice? What is the world coming to?

author: eneuro
author_rank: Super Contributor
timestamp: February 26, 2015, 09:13:56 pm
content: Quote from: calzap on February 26, 2015, 04:22:11 pmClose to my location (a few km away) are 400kV & 200kV transmision lines 50Hz, I guess.Summer time when it i shot outside lowerst lines seams to be not such away above a head.What do you think, which could be safe wire length and is it safe to drive a bike there and keep hands on 0.5 meter handlebars ?I mean touch handlebars to the metal.Probably it is, while someone designed this and probably calculated safe 400kV transmision line distance from the ground, but this HV wire looks very close and it is interesting what level of electric field directly under such 400kV wire 1m above ground could be?

author: Riotpack
author_rank: Regular Contributor
timestamp: February 26, 2015, 09:19:08 pm
content: Quote from: LaserSteve on February 25, 2015, 03:27:06 pmThank you, I'll give this a go. I only really have one shot because I cannot cut it and make another joint due to the very limited length.

author: Riotpack
author_rank: Regular Contributor
timestamp: February 26, 2015, 09:35:22 pm
content: The connectors/joints we use at work are a lot more heavy duty. This is Lead armored 630mm^2 cable with fibre optic strands in the shielding braid.

author: IanB
author_rank: Super Contributor
timestamp: February 26, 2015, 09:49:53 pm
content: Quote from: eneuro on February 26, 2015, 09:13:56 pmUsually those 400 kV transmission lines are higher than they look. Because they are so big they look like they are hanging close to the ground, but if you were able to measure them you would find they are several meters up. Apart from safety considerations, if there was any chance of a tree or vehicle touching them the fault would cause major disruption to the system.

author: CM800
author_rank: Frequent Contributor
timestamp: February 26, 2015, 10:50:23 pm
content: Quote from: LaserSteve on February 26, 2015, 03:11:56 pmThanks for the info Steve, I shall be careful..I forgot to mention the frequency is 20kHz, how much will this change things?

author: LaserSteve
author_rank: Super Contributor
timestamp: February 27, 2015, 02:14:00 pm
content: At 20 KHz, very little.Steve

author: 3roomlab
author_rank: Frequent Contributor
timestamp: February 27, 2015, 03:02:28 pm
content: Quote from: LaserSteve on February 26, 2015, 03:11:56 pmis this HYSOL the same item? there seem to be 3 variants in amazonhttp://www.amazon.com/Loctite-Hysol-Off-White-Two-Part-Adhesive/dp/B004VODQ0Mor thishttp://www.stanleysupplyservices.com/loctite-83200-1373425-1c-hysol-two-component-epoxy-adhesive-kit-white/p/429-823

author: eneuro
author_rank: Super Contributor
timestamp: February 27, 2015, 07:07:28 pm
content: Quote from: IanB on February 26, 2015, 09:49:53 pmMaybe, in sunny day it should be easy find out its height using sun shadows on the ground and calculating sun elevation in my softwareAnyway, I've spare SS495A magnetic field radiometric sensor, so a few line of code on connected AVR will change this thing into spohisticated equipment to detect magnetic field anomaly and diferences as well as its frequency and amplitudes...I wonder what levels and how far away this field is stronegr than earth magnetic field

author: SeanB
author_rank: Super Contributor
timestamp: February 28, 2015, 06:36:08 am
content: Easy way to see the field is to take a T12 flourescent tube and ground the one end with a steel rod of about 1m driven into the ground, then hold vertically under the line on a dark night. T12 as it has a lower breakdown voltage ( but is harder to find as opposed to the T8 and T5 lamps common at the moment) so will light with a lower voltage gradient.

author: IanB
author_rank: Super Contributor
timestamp: February 28, 2015, 07:45:02 am
content: Quote from: SeanB on February 28, 2015, 06:36:08 amKinda like this:https://www.google.com/search?q=field+richard+box&tbm=isch

author: eneuro
author_rank: Super Contributor
timestamp: February 28, 2015, 10:02:37 am
content: Quote from: IanB on February 28, 2015, 07:45:02 amEspeccially like those ones- perfect "unidetified objects" that can confuse even... UFO hunters if we let them "fly" close to the groundHow did they made those nice flourescent blobs?Anyway, high level of electric field is used there, but I'm more interested in magnetic fields levels close to such monster HV transmission lines