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.


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