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11KV Voltage Indicaters

08/14/2011 6:41 AM

Years ago I worked on some old'ish (about 40 years old now) GEC 11KV oil switches that had "voltage indicators" a row of 3 neon's indicating voltage present. They were also used in some of our switching station panels that had no VT's. How did these work please? I think they had something to do with capacitance but old age and Google is getting the better of me.

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#1

Re: 11KV Voltage Indicaters

08/14/2011 7:55 PM

If you do a search on NEON LAMPS you will get a decent smattering of explanations. But your memory is not as bad as you imagine. There are current limiting resistors though, you probably just couldn't see them in your applications.

They still use that technology on the "glow stick" voltage indicators used for testing gear. It's a long stick, basically full of resistors, at the end of which is a neon lamp that will glow if a circuit is energized.

The newest technology though is LED based. We use a product called a Voltage Vision indicator on our MV gear.

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#2

Re: 11KV Voltage Indicators

08/14/2011 11:16 PM

From memory neons strike at about 90Vac, so just have a resistor in series to suit/limit, the (bugger all) draw current after striking.

I think the working range is/was 90 to 130 Vac, draw ~5mA, but don't quote me on that either, as there were a range of sizes, some quite big.

You could use a capacitor as a current limiter. But 11 kV is a bit high for direct connection (esp. in those days)

However; I think it's most likely (at that voltage) that they ran off half a dozen turns of 'bell wire' wound around an insulated conductor. If you like; a 'CT' approach.

This inductive method also limits current after striking.

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#3

Re: 11KV Voltage Indicaters

08/15/2011 4:52 AM

I found my old apprentice training logs and found this in one entry as part of a drawing but not a description of how it worked.

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#6
In reply to #3

Re: 11KV Voltage Indicators

08/16/2011 8:45 AM

By specs it seems my mA recollection was a bit high.

Looks like anything aerial, or plate, like near a 11kV line would provide enough capacitively and/or inductively.

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#4

Re: 11KV Voltage Indicators

08/15/2011 7:20 AM

Assuming these units are mounted on the top of the panels they are most likely ground indicators. They work as follows. If A phase is dark B & C phase will be brighter. Indicating A phase has a ground. If B phase is dark then B phase is grounding, etc. You use to see these installed in a lot of system back in the 50's & 60's. I still use them as a quick indicator for maintenance electricians as to pending issues with systems.

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#5
In reply to #4

Re: 11KV Voltage Indicators

08/16/2011 5:00 AM

That makes sense.

BTW you're right about the age of the gear

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#7

Re: 11KV Voltage Indicaters

08/16/2011 10:57 AM

Even today they are widely used in MV Panels; they are sometimes known as "Live Line Indicators" and are used as a safety measure to indicate a line which is left live inadvertantly. They can be made to wrok on capacitive voltage divider principle too.

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