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Charles Ellson · December 3rd 08, 04:41 PM posted to uk.railway,uk.transport.london

On Wed, 3 Dec 2008 02:30:28 -0800 (PST), wrote:

On Dec 2, 9:55 pm, Charles Ellson wrote:
On Tue, 2 Dec 2008 13:17:18 -0800 (PST), D7666
wrote:

On Nov 30, 4:47 am, Charles Ellson wrote:

relays drop out causing an alarm;

reset up to three times in
succession before someone is sent

Nope.

Well, it's been a few years since someone demonstrated the process to
me.

Respond at first alarm with an emergency fault. At least thats
how we do it on ''my'' bit of underground infrastructure.

The same procedure for both unreproducable trips and persistent trips?

Maybe we are at cross purposes here.

I thought you were talking about earth faults - as in ''fully neggy
earth'' or ''full pozzy earth'' as they like to say - not traction
trips.

Earth faults of the nature I was referring to usually don't cause
traction trips or if they do they are usually single events. These
earth faults are indicated the line *service* control room. They are
responded to at first event as experience suggests they are generally
caused by debris that needs shifting, sometimes by a very recently
deceased mammal, or sometimes by a cracked pot (no not an anorak on
the line) in which case the quick fix is smash the pot right out of it
and sort it out in engineering hours.

Traction trips yes, I agree, they re-close the breakers a couple of
times - maybe it is the three you wrote - before investigating - thats
done by the *power* control room. Moving faults i.e. caused by a train
defect make interesting work - power control room has no indication of
trains.

Aaargh! Some more brain cells have now woken up - I've just realised
that the device I _saw_ demonstrated some years ago was the breaker
operated by shorting the tunnel wires (solenoid drops heavy metal ball
on end of string which yanks out switch - it was a few years ago).
Regarding the above, I was possibly thinking simultaneously of earth
faults and the effect of SCDs; in the case of LU's (nominally)
non-earthed supply it demonstrates some of the reasons why such types
of supply are generally frowned upon and need special protection
measures.