London Banter - Wrong kind of pressure

Richard wrote:

"Steve Pardoe" wrote in message
...
Has anyone got to the bottom of this weird story? Apparently it was on
Channel 4 News last night, but I missed it.

The report I heard was quite clear. The pressure monitoring device in the
oil overflow chamber measured a change in pressure, and assumed that the
rate of change meant that the device was faulty, and shut them down.

This was reported months ago, and a software fix has already been developed,
but is still awaiting safety approval (what a surprise).

In the meantime, a man bleeds off the excess pressure in the chamber to
allow the train to restart.

The Main Transformer is basically a large tank in which the core
and windings sit in oil for cooling and insulation. At the
highest point in the tank is a small chamber designed to collect
any gas present. Once a certain amount of gas has accumulated,
this is detected and the unit is locked out by the software.

This is essentially a simplified version of the traditional
Buchholz Relay fitted to pretty well all traction transformers in
service (use Google if you want to know more) and its purpose is
to detect the early signs of arcing in an attempt to limit
further damage. The collected gas can be analysed and will aid
diagnosis of the fault.

Unfortunately, the c2c units have been causing trips due to air
appearing in the chamber, unrelated to any transformer faults.
The cause is still unclear, but there is a strong correlation
with certain atmospheric conditions - maybe it is like taking the
top off a pop bottle.

Chris
--
Chris J Dixon Nottingham UK

Have dancing shoes, will ceilidh.