On 2016-08-11 12:24, Dorothy J Heydt wrote:
> Squirrels and other critters.
My first job out of college was doing substation design for a
large IOU (investor-owned utility). At the time, there was a big
effort to install owl effigies in substations, in order to scare
off the squirrels. However, they're only a problem at low voltages.
By the time you get up to 69 kV, the phase-to-ground distance was
too large for them to readily bridge.
However, we did have one mammalian outage that owls wouldn't have
prevented. My employer was located in a rather cold region. Transformers
are fairly warm, because of the core and coil losses. One January, a
homeless person climbed the chain-link fence (topped with three strands
of barbed wire) and climbed up to the top of a 115-13.8 kV transformer.
On his way, he grabbed the top of one of the 115 kV bushings.[1]
Amazingly, he lived. As the story had it at the time, when he woke up in
the hospital, there was a long line of ambulance-chasers waiting to help
him sue us.
> And trees.
According to one of my professors, urine[2] released by a bird taking
off from its perch on one phase of a power line can bridge a gap of
meters and is highly conductive.
>
http://www.slate.com/blogs/future_tense/2016/08/11/cybersquirrel1_monitors_animal_attacks_on_technological_infrastructure.html
[1] A "bushing" is something that allows a conductor to pass into the
interior of a piece of equipment. It's generally ceramic.
[2] He called it "birdine", because it combines urine and excrement,
but that doesn't appear to be a real word.
--
Michael F. Stemper
This email is to be read by its intended recipient only. Any other party
reading is required by the EULA to send me $500.00.