Re: MOV lightning arrestor in place of safety gap...MCOV?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "J. Aaron Holmes" <jaholmes@xxxxxxxxxxxxxxxxxx>


Thanks David.  That's probably what I will do, then.
Indeed, these seem like very robust devices and I
suspect they're virtually indestructible in Tesla
service.  And you're right, shipping's the killer on
these.  I'd love to know what the original price was!
More than $1, I'm sure.  These were brand new in boxes
dated 1986.

The datasheet for the newer parts has a diagram of the
guts.  Still, I'm almost tempted to smash one open so
I can see for myself :)  They're pretty well sealed
and don't look like they'll come apart easly.  Not, at
least, without a sledgehammer :)

--- Tesla list <tesla@xxxxxxxxxx> wrote:

> Original poster: "David Rieben"
> <drieben@xxxxxxxxxxxxxxx>
>
> Hi Aaron,
>
> I posted this response to your question Friday
> around 9 AM
> CDT, but the Tesla list appeared to be down most of
> Friday
> and Saturday and I never saw my post appear on the
> Tesla
> list. So, I'm going to repost it here:
>
> Aaron,
>
> I've had experience using these in the place of a
> safety gap before.
> I originally also asked this list about the
> feasability of this idea and
> I believe it was fellow list member Jim Lux? that
> stated that this
> would indeed work, assuming that I had the right
> voltage rating
> of the arrester(s) combo. Anyway, I originally used
> a 12 kV rated
> arrester on my 10 kvA, 14.4 kV pig and it worked and
> didn't
> start "clipping" the output of the pig until I ran
> the input variac
> to the pig over about 85-90 on the 0-100 scale, with
> 100 being
> 280 volts input. It was easy to tell when this
> started happening
> as the output sparks of the coil would start
> "sputtering" instead
> of the constant roar. I now have a single 18 kV
> rated arrester
> (15.6 kV MCOV) that I will be using with my 14.4 kV,
> 15 kVA
> pig, so I don't think that I should be experincing
> much clipping
> with this unit, even with 280 volt input into the
> pig. BTW, this
> 18 kV unit is one of the newer types with the butyl
> rubber ex-
> terior ridges as opposed to ceramic and I think I
> also payed
> more for the shipping of this item than I payed for
> the item itself
> off of ebay. I think I only ended up with < $12 in
> it, total. I
> was able to test it for functionality with an x-ray
> transformer
> being slowly ramped up with a variac and it does
> start to clip
> the voltage around 20 to 25 kV.
>
> The guts of these things are interesting and appear
> to be several
> seriesed cylinders of some type of refractory
> (almost like cement)
> semiconductor material which are pressed against
> each other in linear arrange-
> ment with a strong spring at one end of the arrester
> housing. There
> is usually also some ceramic ring spacers and a
> couple of bronze
> disc between each of the refractory semiconductor
> cylinders
> to act as a controlled spark gap between each
> cylinder, I assume.
>
> I think that your idea should work fine if you
> series enough of them
> that their rated peak voltage equals or slightly
> exceeds the output voltage
> rating of your pig. In your case, 4 or 5 of the 3 kV
> rated ones in series
> would probably work just fine :^))
>
> David Rieben
>
> PS-Overvolting these arresters does NOT harm them as
> that's exactly
> what they're designed to do on the utility primary
> line. Once the line
> voltage
> drops back below their cutoff voltage, they act just
> like an open circuit
> once again.
>
> ----- Original Message ----- From: "David Rieben"
> <DRIEBEN@xxxxxxxxxxxxxxx>
> To: "Tesla list" <tesla@xxxxxxxxxx>
> Cc: "David Rieben" <DRIEBEN@xxxxxxxxxxxxxxx>
> Sent: Friday, April 29, 2005 9:29 AM
> Subject: Re: MOV lightning arrestor in place of
> safety gap...MCOV?
>
>
> >Aaron,
> >
> >I've had experience using these in the place of a
> safety gap before.
> >I originally also asked this list about the
> feasability of this idea and
> >I believe it was fellow list member Jim Lux? that
> stated that this
> >would indeed work, assuming that I had the right
> voltage rating
> >of the arrester(s) combo. Anyway, I originally used
> a 12 kV rated
> >arrester on my 10 kvA, 14.4 kV pig and it worked
> and didn't
> >start "clipping" the output of the pig until I ran
> the input variac
> >to the pig over about 85-90 on the 0-100 scale,
> with 100 being
> >280 volts input. It was easy to tell when this
> started happening
> >as the output sparks of the coil would start
> "sputtering" instead
> >of the constant roar. I now have a single 18 kV
> rated arrester
> >(15.6 kV MCOV) that I will be using with my 14.4
> kV, 15 kVA
> >pig, so I don't think that I should be experincing
> much clipping
> >with this unit, even with 280 volt input into the
> pig. BTW, this
> >18 kV unit is one of the newer types with the butyl
> rubber ex-
> >terior ridges as opposed to ceramic and i think I
> alos payed
> >more for the shipping of this item than I payed for
> the item itself
> >off of ebay. I think I only ended up with < $12 in
> it, total. I
> >was able to test it for functionality with an x-ray
> transformer
> >being slowly ramped up with a variac.
> >
> >The guts of these things are interesting and appear
> to be several
> >seriesed cylinders of some type of refractory
> semiconductor
> >material which are pressed against each other in
> linear arrange-
> >ment with a strong spring at one end of the
> arrester housing. There
> >is usually also some ceramic ring spacers and a
> couple of bronze
> >disc between each of the refractory semiconductor
> cylinders
> >to act as a controlled spark gap between each
> cylinder, I assume.
> >
> >I think that your idea should work fine if you
> series enough of them
> >that their rated voltage equals or slightly exceeds
> the output voltage
> >rating of your pig. In your case, 5 of the 3 kV
> rated ones in series
> >would probably work just fine :^))
> >
> >David Rieben
> >
> >PS-Overvolting these arresters does NOT harm them
> as that's exactly
> >what they're designed to do on the utility primary
> line. Once the line voltage
> >drops back below their cutoff voltage, they act
> just like an open circuit
> >once again.
> >