In message , Roland Perry
writes

The report I saw said the grid fault was at Wimbledon. Is it possible
that most of the Underground's power is brought in that way - it would
plumb into the existing wiring from Lots Rd rather easily.

I don't believe so - in fact traction current on the District's
Wimbledon branch is supplied by Railtrack, IIRC.

When plans for closing Lot's Road were drawn up it was stated that there
would be three bulk supply points on the National Grid for London
Underground, any two of which could keep the system running if there was
a failure - so I guess at least two supply points must have failed.

(The effects of the power cut seemed to be very localised - we live only
2 or 3 miles from Wimbledon and were not affected at all).

--
Paul Terry

"Paul Terry" wrote in message
...

When plans for closing Lot's Road were drawn up it was stated that there
would be three bulk supply points on the National Grid for London
Underground, any two of which could keep the system running if there was
a failure - so I guess at least two supply points must have failed.

So, triple redundancy (almost) like you have on airliners.

Three separate feeders into each supply point would be ideal, or two with a
standby generator and a UPS as an alternative.
--
Terry Harper, Web Co-ordinator, The Omnibus Society
http://www.omnibussoc.org
E-mail:
URL: http://www.terry.harper.btinternet.co.uk/

On Fri, 29 Aug 2003 14:25:37 +0000 (UTC) someone who may be "Terry
Harper" wrote this:-

When plans for closing Lot's Road were drawn up it was stated that there
would be three bulk supply points on the National Grid for London
Underground, any two of which could keep the system running if there was
a failure - so I guess at least two supply points must have failed.

So, triple redundancy (almost) like you have on airliners.

Three separate feeders into each supply point would be ideal, or two with a
standby generator and a UPS as an alternative.

In a building a UPS will typically only support small loads for a
short time. This is to allow standby generators to get going, even
if it takes a while to get them going (the things can perform
faultlessly when tested with a simulated mains failure every month
and then refuse to start with a real mains failure).

Typically the standby generator can only power a small part of the
building load. Non-essential circuits are shed as the generator
starts up. With the generator running it may not be desirable to go
back to the external supply automatically if it does become healthy,
it might fail a minute later. Thus the building may run with only
essential circuits for some time until people are happy with the
external supply.

Trains consume large amounts of electricity. I hate to think what
size the battery bank would be to run a railway on UPS. There would
not be a standby generator, but a standby power station. Think in
terms of the size of some of the old ones.


--
David Hansen, Edinburgh | PGP email preferred-key number F566DA0E
I will always explain revoked keys, unless the UK government
prevents me using the RIP Act 2000.

In article , David Hansen
writes
Typically the standby generator can only power a small part of the
building load. Non-essential circuits are shed as the generator starts
up. With the generator running it may not be desirable to go back to
the external supply automatically if it does become healthy, it might
fail a minute later. Thus the building may run with only essential
circuits for some time until people are happy with the external supply.


In these days where everything is computer controlled and your servers
are probably the most important business-critical device (see the cases
of various supermarkets which have to close for the day because their
accounting software is on the frizz), keeping them working also needs
air-conditioning. So when things like this happen you'll be sitting in
the dark, bathed only by the strangle glow of computer screens, unable
to do many jobs that require manual dexterity - like going for a pee in
a totally dark toilet - but in a nice, comfortably cooled environment.

--
Martin @ Strawberry Hill

In article , Martin
writes
In article , David Hansen
writes
Typically the standby generator can only power a small part of the
building load. Non-essential circuits are shed as the generator starts
up. With the generator running it may not be desirable to go back to
the external supply automatically if it does become healthy, it might
fail a minute later. Thus the building may run with only essential
circuits for some time until people are happy with the external supply.


In these days where everything is computer controlled and your
servers are probably the most important business-critical device (see
the cases of various supermarkets which have to close for the day
because their accounting software is on the frizz), keeping them
working also needs air-conditioning. So when things like this happen
you'll be sitting in the dark, bathed only by the strangle glow of
computer screens, unable to do many jobs that require manual dexterity
- like going for a pee in a totally dark toilet - but in a nice,
comfortably cooled environment.

Personally I have no problem going for a pee in a dark toilet - neither
do totally blind people. However it is recommended that men sit down on
this kind of occasion.



--
Five Cats

On Sun, 31 Aug 2003 12:35:44 +0100 someone who may be Martin
wrote this:-

In these days where everything is computer controlled and your servers
are probably the most important business-critical device (see the cases
of various supermarkets which have to close for the day because their
accounting software is on the frizz), keeping them working also needs
air-conditioning.

I have been involved in some rather large computer installations.
The halls concerned were air-conditioned. It is a matter of debate
whether such air-conditioning is necessary or, because the
specifications are very difficult to maintain over time, a get-out
clause for the manufacturers.

In the case of a supermarket there is no need for air-conditioning
of the small server(s) concerned. All that is needed is adequate
ventilation. It is, of course, sensible to place this ventilation on
the essential side of the busbars, to ensure that the room and hence
the servers do not become too warm.



--
David Hansen, Edinburgh | PGP email preferred-key number F566DA0E
I will always explain revoked keys, unless the UK government
prevents me using the RIP Act 2000.