We had a power cut to the upper campus Monday. Here's how our network engineer described it:
During the Monday power shutdown I went to the 21 KV substation
to see what trouble looked like. This is an area surrounded
by a chain link fence and a gate that is normally locked. Today,
it is open and lots of vehicles are parked there. The device demanding
attention looked like a prop from an early B&W episode of the
Doctor Who TV series on PBS. See attachment.
A cover and steel beams had been pulled off an outdoor pit exposing an underground
stainless steel cylinder. At least, it looked like
stainless -- I wasn't touching it and I sure wasn't going
into the pit. The bottom of the pit contained several
inches of rain water (or some similar fluid). Nine cables
the size of my arm attach to the lid. One feeder has three
cables; this switch had two inputs and one output. A sign on
the lid says something about vacuum switch but the electricians
were calling it a 'troger switch.'
The electrician in the pit with the beast said to look at
the white deposits on the high voltage connectors. I didn't
see any. Still, I'm not going into the pit.
So the problem is that arching begets more arching. A pit
inspection had disclosed an audiable electrical hiss. That is
a runaway condition. When the arc has eaten a hole of
sufficient size, there is a massive flash over and catastrophic
As I watch, the electrician gets out a small spanner wrench and
trys to unscrew the suspect connector. It doesn't move. He gets
out a torque wrench and connects it as a lever on the spanner
and pushes on the connector til a piece breaks off. That is
handed out of the pit and passed around to all who are watching.
This is a typical repair scenario: one guy working, 4 guys
watching and giving advice. There is a track along the
bakelite sliver that shows that there has been arching.
The broken connector was installed by PG&E and is as old as
anything else on campus.
The function of this switch is to allow either or both of
the pair of incoming HV lines to be switched along toward
a single "recloser". This is a gangly switch on steel
legs that used to be PG&E's last circuit breaker. The
power on the campus side of the recloser goes through
another Dalek switch. So it looks like:
Feeder-1 =======\ /===== Transformer 1 \ / ======== Recloser ========= /Switch Switch \ Feeder-2 =======/ \===== Transformer 2