Back in the '60s, working on a sground sattion for satellites, I was, as an
apprentice, involved in testing the crowbar on a 22kV 3Amp supply.
We dumped a 24 microfarad capacitor through a 10 ohm resistor and ignitrons.
Said resistor was a 'globar' type, 3 inches in diameter and 14 inches long. It
was attached by straps of copper 3/16 thick to a fibre glass board 1/4inch
thick. After some 250 discharges, there was an explosion, and the resistor
disintegrated, with half of it departing through a 1/8 inch thick pressphan
sheet and going some 20 feet across the lab. I was a bit dubious when I could
see sparks running across its surface.....
I've been a bit dubious about crowbars ever since...
73
Peter G3RZP
========================================
Message Received: Oct 02 2007, 08:19 PM
From: "Jim Tonne"
To: "Karl-Arne MarkstrÃm" , amps@contesting.com
Cc:
Subject: Re: [Amps] 8877 Grid Trip timing
Karl-Arne wrote in part:
> . . . short circuit the 14 kV 15 A rectifier using a
> 0,3 mm silver wire, which should not burn off or
> melt. This obviously required some courage by
> the maintenance personnel.
That brought back a memory of my first exposure to
crowbars (also using iggies).
It was at Continental and it was a very long time ago.
I had never heard of crowbars and they were getting
me up to speed on the innards of high power as
compared to lowpower [50 kW or less] which was
my background to that time.
My boss went around, telling everyone that I was
about to learn how to test the crowbar. He told
everyone in earshot to get their earplugs, or at least
get ready to plug their ears. I think he winked at
each of them but of course I didn't know that. He
looked at me with a look of pity, poor boy, you
can't hold the stick to do the shorting and also plug
your ears so you'll just have to tolerate the noise.
So I got up my courage at the right moment and
shorted the high voltage. It silently tripped off. All
the meters went to their standby readings. I guess
the HV transformer kind of grunted. But not a
sound excepting for LOTS of laughing about how
they had got me all prepared for a huge mess and
how nervous I ought to be.
Clowns!
- JimT
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