High Voltage Relays

[recalli349]

I have attached a picture of a circuit where a hi-pot is applying 4800VAC to a transformer. Also in parallel with that 4800VAC rms are two wires heading into a 600VAC rms multiplexer. I have one relay on each line. The 4800VAC is only applied when the relays are both open. I am not sure of the type of relay that I should get. I am thinking that it should be able to withstand at least 4800VAC rms while open, and then operating voltage should be at least 600VAC (since that is max capability of the multiplexer). Is this thinking correct or can I use a relay with a smaller voltage rating? All help is appreciated.

Thanks

 

[Skogsgurra]

This is too much!

Are you kidding?

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[recalli349]

Haha, definitely not kidding. What exactly do you mean by too much? I wanted to be as specific as possible.

 

[crshears]

Hey there recalli349,

What kind of circuit is this?

Are you asking about what type of switching device to use to ensure that the 4.8 kV potential is never applied to the 600VAC multiplexer? If in fact that is your question, it is your use of the word "relay" that is throwing us off.

I don't profess to have a great deal of the type of experience applicable to your question, but I have only ever seen that high a potential switched using either a circuit breaker or fuse-equipped cut-out switch. As near as I can tell, what you'd want to have is a ganged disconnect switch interposed between the transformer winding to be hi-potted and the multiplexer, the operating mechanism of which incorporates a 'b'-type position or limit switch wired in such a way that the 4.8 kV supply cannot be applied to the unit under test unless the interposing switch contacts are open.

Hope this helps.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[ScottyUK]

I would suggest using a switch in each pole as a disconnector, and a second switch driven in anti-phase applying a circuit earth to each pole on the 600V side of the system. That way there is a much reduced possibility of HV finding its way to the LV side due to capacitive coupling or leakage.

Gigavac have some multi-pole HV relays which look like a plausible solution to integrate all four switching devices in one package.

 

[Skogsgurra]

By kidding, I mean that your diagram seems to show 4800 V being connected to the 600 V mux when the rightmost contact closes.

That is definitely too much - in several senses.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[zappedagain]

You want a 600V relay that is designed to pass a 4800V hi-pot test.

Z

 

[waross]

Scary on several perspectives.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

You want a 600V relay that is designed to pass a 4800V hi-pot test.

Untrue. You want a relay that is designed for 4.8kV service voltage. A hipot test is a one-off or very infrequent withstand test, not a routine operating condition. You're using the component at 4.8kV in a routine operating state. A 600V relay will not have adequate clearance or creepage distances for service at 4.8kV.

 

[recalli349]

Thank you for the responses everyone. The relays would only close once the hi-pot has been turned off. The relays will never pass 4800VAC. I am just wondering if 4800VAC is applied to those two relays (when open), what would the requirements of the relays have to be to ensure that breakdown does not occur. I am not an expert nor an intermediate in this field. If there is something alternative to a relay that would work better, then I will research into that.
ScottyUK, these Gigavac devices look great. Thanks!