[ RadSafe ] Arresters, spark gaps for Rich Wagner
NiagaraNet at aol.com
NiagaraNet at aol.com
Wed Apr 28 20:54:00 CDT 2010
Please post and thnx.
Here you go Richard.
For the behalf of Richard Wagner,
Subject: Help with Westinghouse SV type arrestor
Found a few Westinghouse lightening arrestors that read about 400 uR/hr
on an ion chamber and maximally 2000 cpm on a 44-9 G-M.
Any idea about what isotope may be inside of them?
Here's some information that I've obtained from :
Joe Osterhout Consulting
In a message dated 4/28/2010 8:44:08 A.M. Eastern Daylight Time,
joeosterhout at att.net writes:
It was most likely manufactured before 1970 to have the brown porcelain.
That size porcelain would house anything from 3 to about 18 kV.
The name tag which contains full identification is mounted on the ground
end casting if W, but this one looks like the nametag is on the separate
angle bracket at the base.
Don't attempt to read the nametag while energized except possibly by a
mirror on an insulated stick.
If W and before 1970, it is either type SV (1950 - 60) SVT (1960 - about
69) or CPL (1969 - about 1980).
SV was passive spark gap, SVT and CPL active (current limiting) spark gap.
It is not likely modern solid state technology.
OK, so you have a 5 kV type SV arrester.
They contain a series of spark gaps made of formed brass plates with ring
shaped resistor spacers and silicone carbide nonlinear resistors in series
with the spark gaps.
The spark gaps are insulating at normal system voltage, then when voltage
approaches a dangerously high level - like due to lightning, the gaps
spark, conducting the lightning current to ground. After the lightning current
has passed (typically 10,000 A or less with duration of 40 microseconds or
less), the current due to power system voltage is limited to 100 A or so by
the silicone carbide resistors - allowing the spark gaps to stop
conducting following the next natural power system voltage zero point - returning to
the original insulating state and ready to perform again at some future
Depending on age of the arrester - not seen on your nameplate photo - the
arrester may contain radium salts painted unto the spark gap pates (pre
1960) or if not, then perhaps what you have is something in the porcelain
I suggest that you hold a cheap radio tuned to about 1000 AM within 10
feet of the arrester. If there is radio noise, the arrester is in danger of
failing and should be replaced.
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