Electronics > Projects, Designs, and Technical Stuff

Open HV Probe 40kV

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PartialDischarge:

--- Quote from: tggzzz on April 21, 2019, 11:50:45 am ---However, since there are so many parameters (e.g. frequency, porosity, surface texture) involved, I don't see how the dielectric constant can give any useful predictive information as to the maximum voltage that such a probe could withstand. I presume measurements would have to be done, and I would be surprised if many amateurs have appropriate equipment.

--- End quote ---

Oh yes it totally does, again because it defines how field lines will distribute, and they determine when breakdown occurs. HV is a very smart and will not condone mistakes. Once you have a mechanical design with all the elements in place, you have to study the thickness and breakdowns of the materials in question (air is also a 'material' here). These elements create capacitors and each one has its limit at AC.

A 40kv unshielded probe like the one here is not that difficult to design (as long as the resistive element is well chosen) because distances are big, the distance between the hv pole and ground is huge and the 'usage time' is going to be low.

Also not talked about is this: what kind of 40kV are we talking about? because not all 40kV are created equal.I would not use *any* kind of these probes (even commercial ones) on a distribution 40kV power line. The energy here is very high and makes things more complicated.

beanflying:

--- Quote from: MasterTech on April 21, 2019, 12:25:25 pm ---
--- Quote from: tggzzz on April 21, 2019, 11:50:45 am ---However, since there are so many parameters (e.g. frequency, porosity, surface texture) involved, I don't see how the dielectric constant can give any useful predictive information as to the maximum voltage that such a probe could withstand. I presume measurements would have to be done, and I would be surprised if many amateurs have appropriate equipment.

--- End quote ---

Oh yes it totally does, again because it defines how field lines will distribute, and they determine when breakdown occurs. HV is a very smart and will not condone mistakes. Once you have a mechanical design with all the elements in place, you have to study the thickness and breakdowns of the materials in question (air is also a 'material' here). These elements create capacitors and each one has its limit at AC.

A 40kv unshielded probe like the one here is not that difficult to design (as long as the resistive element is well chosen) because distances are big, the distance between the hv pole and ground is huge and the 'usage time' is going to be low.

Also not talked about is this: what kind of 40kV are we talking about? because not all 40kV are created equal.I would not use *any* kind of these probes (even commercial ones) on a distribution 40kV power line. The energy here is very high and makes things more complicated.

--- End quote ---

Most definitely not for high energy mains testing. I posted a link to the Ohmite Resistors planned in post Number 1 from memory. Also this option is unlikely to see use above mains frequencies as accuracy will go down the tubes. Typical use is in CRT testing and maybe Neon or similar Transformers are most likely the upper limit at 15kV?

Unless a containment of some sort allows tracking to occur the material seems up to the task. I am considering epoxy filling the tip where the resistors will sit but it won't add much in the way of safety over the air gap and distance along the probe from the users hand.

Zero999:
I wonder if adding a suitable lacquer will help with the poor finish created by the 3D printing process? I imagine some kind of polyamide would be ideal.

PartialDischarge:
Some thoughts about the energy of high voltage sources. I have been zapped many times by some low energy kV sources, like power supplies and 2 or 3kV CRT rails. While it hurts, meh, its no big deal.
Now, a guy named Eduardo Garcia was electrocuted by a power line, only 2.4kV . There is a documentary (available in torrents ) with graphic real images and it is just unbelievable what it did to him, lost an arm and a lot of flesh in the body. And this is only 2400 freaking volts, most medium voltage lines in Europe within cities are 20000V

https://www.imdb.com/title/tt6105406/

bd139:
Ah that dude. On the other end of a bear shaped capacitor as well. quite horrifying that one.

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