11KV Voltage Indicaters

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.

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.

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.

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.

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.

That makes sense.

BTW you're right about the age of the gear

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.