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I'm finding a relay which can withstand 10kV when the contacts are open. But all I found for now can't achieve this.

I'm considering to use several relays with lower rating in series to achieve this. But I've never used it like this, nor saw others done this.

Would I be exceeding any absolute maximum ratings with relays in series?

Would this be safe?

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    \$\begingroup\$ Recommendations? No... not here. You're welcome to take this question to our EE.SE chat. I'd be happy to post some leads for you to the chat. \$\endgroup\$ – Nick Alexeev Jun 20 '17 at 1:17
  • \$\begingroup\$ based on AC air gap of 1kV/mm +/- 50% depending on dust level you would need to define the load type reactance and current 1st then breakdown voltage why you need such a level if due to LdI/dt or input voltage. then as @Kevin correctly states, a vacuum relay is best bet. \$\endgroup\$ – Tony Stewart EE75 Jun 20 '17 at 4:21
  • \$\begingroup\$ @NickAlexeev, I've edited the question. I wonder why my question is still "on hold", can someone vote it reopen, please. \$\endgroup\$ – diverger Jun 21 '17 at 7:28
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You can't connect several relays in series to get a higher voltage rating for pretty much the same reason why you can't put relays in parallel to increase current rating. Multiple relays will never open/close at exactly the same moment, and the first one to open under load will be exposed to the full voltage, which will damage it soon enough.

Just find a relay / contactor with the appropriate ratings and use that. Googling for "10 kV relay" or "10 kV contactor" yields lots of results, ranging from official Siemens Power Distribution catalog to parts of dubious pedigree on Aliexpress.

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There are quite a few around from speciality vendors such as HV Relays

They use a vacuum to ensure the air doesn't break down between the contacts. [10kv relay][2]

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  • \$\begingroup\$ With 10 kV, breakdown can occur in places other than the contacts, such as between the HV and the relay coil or between the HV and the relay structure. I would refer you to the old Cal Tech lightning lab, where they created monster high voltage pulses by charging capacitors in parallel, then switching them to series so they could test high voltage components used in power transmission. They did not buy those switches at Home Depot! Alas, the lightning lab is gone now. \$\endgroup\$ – richard1941 Jun 20 '17 at 9:35
  • \$\begingroup\$ @richard1941 A Marx bank? I believe there is one at Manchester uni. 10KV is fairly routine in vacuum relays, Jennings will have something that can handle it easily, providing you are cold switching. Hot switching that sort of thing at any real current is a much bigger headache, think pressurised SF6 and very large actuators to get the contacts apart fast enough to quench the arc. \$\endgroup\$ – Dan Mills Jun 23 '17 at 12:27
  • \$\begingroup\$ Off topic, but a long time ago I had an old military antenna tuner that had a vacuum capacitor. Jennings Radio was a local company. They had just been taken over by IT&T, but old man Jennings still had an office there. He went to a big box, fished a capacitor out, and said, "Use this one; it has the same capacitance and a slightly higher voltage rating," and just gave it to me. I did, and it worked great on 40M. That antenna tuner was really something: the coils were solid silver, mounted on a rotating shaft with a rolling contact. I could use that thing now. K6YVL \$\endgroup\$ – richard1941 Jun 24 '17 at 16:28

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