My local scrap metal yard sees an amazing array of gizmos.
For some months i watched what i assumed to be high voltage power line bushing, thinking if the insulator rings weren't broken it'd make a nice mounting base for a birdbath or sundial.
Well, one day the owner (Calvin) cut it in two with his giant diesel powered pincer. It was full of strange looking things so out of curiosity i brought home some of the parts. At thirty cents a pound one can indulge his curiosity.
Anybody who's been around switchyards has heard of a "Capacitive Coupled Potential Device".
It looks like a transformer bushing
but it actually houses a voltage reducing circuit that allows one to measure those hundreds of kilovolts with ordinary meters.
The series capacitor string inside the bushing divides the high voltage down to something manageable at the tap, perhaps 20kv which one can further reduce to 120VAC with an ordinary transformer and read with everyday meters.
Here's what it looked like when i got it home.
Who could resist taking that apart ? Looks like a trove of Tesla coil parts !
Each deck is a pair of small capacitors in parallel-series, the little green buttons
and judging by the glass insulators, they're high voltage parts. Their part number is cryptic so I've emailed an inquiry to Sprague...
The blue&gray stacked cylinders are connected in parallel with the capacitors, as are the smaller black cylinders. What on Earth were they for?
Ancient and barely readable instruction leaflets suggested there'd be a spark gap to protect against overvoltage
http://www.electricalpartmanuals.com/pdf/transformer/Westinghouse/Arresters and Capacitors/DB39631.pdf
and if you're going to strike an arc around power equipment you'd darn well better provide something to limit the fault current !
Sure enough,
the grey cylinder turns out to be a 2 kohm resistor, presumably to limit current to <around 100 amps ?
that thing would absorb
tremendous wattage for the milliseconds it takes to clear a fault
and the blue cylinder indeed turned out to be a stack of spark gaps,
note the copper horns, so carefully spaced with a plastic separator piece
The coil around the center layer of spark gap i figure is to help extinguish the arc.
it's wound in direction that its MMF by right hand rule pushes the arc toward the center, where the horns diverge.
That makes the arc longer and surrounds it with ceramic to help absorb heat and extinguish the arc. The gray cylindrical resistor takes the brunt of a fault, limiting the current to a value that won't blow up this blue arc arrestor.
Basic Physics Rules !
This one showed minor burn marks and there was one charred wire nearby, probably the reason this CCPD was in the junkyard. It didn't blow up , though !
The black cylinders are in parallel too, and i believe them to be high megohm bleeder resistors to prevent DC buildup on the capacitors. I don't have an ohmmeter that'll measure them. They're hard ceramic, probably silicon carbide. They need to be tall to keep the kilovolts per inch within reason.
So - i had an afternoon's entertainment for just a few bucks.
Had i known it was CCPD i'd have brought it home before Calvin crushed it. I believe a fellow's heirs should scratch their heads in wonderment at the estate sale.
I mailed a couple parts to dlgoff for his museum, put some in my high voltage pile. I have ten pounds of #30 magnet wire for a Tesla coil...These high voltage caps might be handy for that, amateur Tesla enthusiasts make their own out of window glass.
Maybe Don will post a pic of the neat 10KV capacitor.
So - while this was hardly a beautiful piece of equipment, i'd say the thought that went into it has beauty.
old jim
Here's a good pic of it.
