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Kearney 3kV MCOV distribution surge arresters - new in boxes!

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J. Aaron Holmes

Sat Jun 07 2008, 12:58PM

Registered Member #477 Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546

Perfect for protecting your MOT from lightning strikes!

I have about a dozen of these suckers, brand new in factory boxes and complete with pole mounting hardware! WOWWWW!!!

...ok, they're really not *that* exciting

They're rated 3kV MCOV, obviously meant for an old 2400/4160Y system. The company is Kearney, which has been absorbed into Cooper. The boxes have various dates on them, but all from 1977, I believe. Internally, these are MOV-based, having a single large silicon carbide disc held in place with spring-loaded contacts. I know this because I couldn't resist breaking one open with a sledgehammer once! (that was pretty lazy, but I had extras)

Anyway, if folks are interested in these, PM me. $10 plus actual shipping charges (which will include a few $$ for packing materials). The $10 is really just a miserable attempt at motivating myself to go to the post office for you

Cheers,
Aaron, N7OE

rp181

Sat Jun 07 2008, 04:26PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

ummmm... what do these exactly do? protect from power surges?

J. Aaron Holmes

Sat Jun 07 2008, 11:46PM

Registered Member #477 Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546

rp181 wrote ...

ummmm... what do these exactly do? protect from power surges?

Indeed yes; surge arresters do arrest surges!

I should correct my prior post a little; they operate on the same principle as MOVs (which is what the more modern arresters use), however silicon carbide (SiC) is NOT metal oxide.. In either case, the intent is to look like an open circuit below a certain voltage, and a short circuit above. So when a high-voltage impulse from, e.g., lightning comes along, the arrester becomes very conductive, effectively shorting out the spike. This protects whatever device the arrester is in parallel with, such as a pole pig. The conductivity of MOV is a much more exponential function of applied voltage than SiC, which is why MOV is preferred nowadays (faster response time). Also, these old ceramic-body ones hold together well even when the guts are totally blown away by powerful surges, which makes it hard to spot the dead ones. By comparison, the new polymer and rubber-encased ones will be visibly melted when dead.

You have been enlightened

Cheers,
Aaron, N7OE

rp181

Sat Jun 07 2008, 11:51PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

ahh, i see.
Thank you for enlightining me

Andyman

Sun Jun 08 2008, 02:10AM

Registered Member #1083 Joined: Mon Oct 29 2007, 06:16PM
Location: Upland, California
Posts: 256

Would they work on a NST filter circuit?

J. Aaron Holmes

Sun Jun 08 2008, 02:27AM

Registered Member #477 Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546

Andyman wrote ...

Would they work on a NST filter circuit?

Yes. Or, at least, people do use them for transformer protection in Tesla coils. I never have, but I'd be inclined to use them more as an auxiliary measure (like in place of the MOVs in a Terry Filter) than as a replacement for a safety gap. Safety gaps are nice because you can actually see them operate.

David Rieben uses an arrester as protection for his pole pig:

The arresters I'm offering here (mainly because somebody asked about them, by the way) are pretty weak on the voltage side, so you'd need a few. And a few of these combined weigh more than most NSTs, I think! The cool thing would be a newer, higher-voltage polymer type like David has, and these do pop up on eBay from time to time. Case in point:

...and my latest pole pig came with one bolted to the side (which I've since removed, but hey! Bonus!!):

Search for "arrester" in the Business and Industrial section of eBay and you'll see a few more surge arresters pop up, too. Some of these are HUGE substation-class behemoths.

Cheers,
Aaron, N7OE

Steve Conner

Sun Jun 08 2008, 10:35AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Do you think it would be possible to remove the guts and make a mini oil-filled Tesla resonator out of one?

J. Aaron Holmes

Sun Jun 08 2008, 12:44PM

Registered Member #477 Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546

Dr. Conner wrote ...

Do you think it would be possible to remove the guts and make a mini oil-filled Tesla resonator out of one?

Maybe. The inner diameter is only 1.5" or so, IIRC. So it would definitely be mini! I'm generally dubious of the oil-tight-ness of the ends, but that can probably be managed with science

I've got some 21kV ceramic ones, too. They're about 18" long and weigh about 80 lbs, though. Nobody wants to pay for shipping on those babies, I'm certain of it!

Cheers,
Aaron, N7OE

FIFTYGUY

Mon Jul 07 2008, 03:28AM

Registered Member #1226 Joined: Sat Jan 12 2008, 03:32AM
Location: Virginia
Posts: 2

Something you probably missed when you dissected your 3kV Kearney arrestor: they contain a live .22LR blank. I assume from the construction that when enough current passes through the blank's rim or when it gets exposed to enough heat, it blows the guts of the arrestor out via the crimped-on end-ring (towards your wrist in the photo).

I know because a bunch of these made it down my way as surplus. I hooked an NST up to one to verify operation, so presumably the 30mA or so were insufficient to blow the blank. But using them as filters for big TC's would probably give you a big surprise! I guess you could remove the blank and re-assemble the thing. Or take a bunch of them apart and put all their *BIG* SiC elements in one tube end-to-end,

J. Aaron Holmes

Mon Jul 07 2008, 04:56AM

Registered Member #477 Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546

Yeah, somebody else mentioned the same a while back. When I smashed one open, I definitely missed the .22 shell, if there was one. Honestly, a .22 shell makes no sense to me. These are arresters, not fuses; their job is to make a connection, not break one. I may have to smash another one open to end all speculation. I definitely *have* heard of fuses with explosive charges in them...

EDIT: Damn. Shoulda just taken your word for it

I busted another one open just for kicks (I'm not short on these things), and indeed there is live ammo inside.

Here's the end cap disassembled:
End Cap

Here's the bottom terminal removed. I don't think I ever took this part off before; it's fairly hard to do.

And here's the blank, unscrewed with a very gentle twisting:
Shell

So! There you have it. However, I'm not sure about the intent of the blank. It seems really unlikely that it would be meant to fire during normal operation, doesn't it? Destroy the arrester on the first surge? Hmmm... maybe it was intended to destroy the arrester only after long-duration operation, such as when the arrester failed to open following a surge? I'm even a bit unsure what "destroy" means in this case, since the position of the blank is so odd. It's separated from the "guts" by a large metal plate (see top picture), and the guts are spring-loaded, too, so it seems like they'd be protected pretty well. I'm left to wonder if the terminal containing the blank was meant to be completely blown off (seems really unlikely), or if the blank's firing was simply intended to "poison" the atmosphere within the arrester, making it non-conductive ...? Maybe the blank contains some special "stuff"

Well, it is an interesting little mystery, isn't it?

Finally, just because it's kind of neat, here's a picture of the SiC cyllinder (the actual varistor element):
SiC

So... if anybody wants one of these, just make sure it's not illegal for me to ship you live ammunition!

Cheers,
Aaron, N7OE

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