On Apr 15, 8:28*pm, David Hansen
wrote:
On Tue, 13 Apr 2010 10:48:59 -0700 (PDT) someone who may be The
Gardener wrote this:-
Like a lot of things on the railway, its origins are historical. 650 V
was the highest value of "medium" voltage under the old Factories Act,
which meant that (at that time) a permit-to-work system was not
required for "live" work. Such a system of work would these days be
illegal under the Electricity at Work Regs, of course.
That is rather amusing on a railway line equipped with unprotected
conductor rails energised at a nominal 750 V d.c. (For those who
don't know unprotected conductor rails are one of the very few
exemptions under the Electricity At Work Regulations 1989).
The policy for main lines now is that the distribution systems have
either a PSP at each end (WCML practice) or a PSP at one end and an
auxiliary PSP (APSP) at the other (Western practice), to enable
resupply in the event of a failure. In particular, a dual-fed system
will allow a faulted cable section to be isolated and the two sections
to be fed from each end.
Do you know if switching is automatic, remote,or manual? Perhaps the
answer is, it depends:-)
Thanks for taking the time to produce a comprehensive posting. I
found it very interesting.
--
* David Hansen, Edinburgh
*I will *always* explain revoked encryption keys, unless RIP prevents me
*http://www.opsi.gov.uk/acts/acts2000...#pt3-pb3-l1g54
In response to your query about switching, the WCML system has
automatic switching, whereas the (significantly cheaper) Western
system has manual switching. At the moment, these are the only routes
where reconfigurable supplies have been provided. In the case of the
Western, this is slowly being rolled out across the system's main
lines and is in use of the lines south from Gloucester towards Swindon
(the first significant application and primarily as a testbed) and
Bristol, for example.
Present policy is that if the average cost of delay minutes on a route
exceeds a certain amount, then at resignalling, a reconfigurable
system is to be provided. This is a fairly recent change of policy,
which is why it has only been applied extensively on the WCML. The
Western schemes are not, generally, associated with resignallings
(except for the new scheme in the Newport area) but are the result of
a policy to improve the availability and reliability of sigpower
schemes.
In response to some other queries raised:
The 650 V system supplies all signalling and telecoms loads,
interlockings and point machines. In addition, a certain level of
emergency lighting at relay rooms is also supplied off the 650 V
system. The power supply arrangements at level crossings varies; at
some sites all the equipment is supplied from the 650 V system and at
others, only the signalling interlockings, with the barriers and
lights supplied directly from the mains. Owing to the risk of wrong-
side failures caused by a loss of supply, level crossings apart from
AOCL and ABCL are fitted with battery back-up and the equipment is
supplied directly from the battery, in the manner of a UPS. Telecoms
loads are also usually fitted with battery back-up.
One of the problems with a three-phase system is that all UK approved
signalling equipment is single-phase, and given that point machines
tend to have much higher loads than any other equipment (typically 2-3
kVA, whereas most other equipment has demands in the tens of VA), load
balancing is difficult. In the case of level crossings, three-phase
battery chargers are used. As to why we don't use three-phase point
machines, the answer is I don't know, apart from that there are no
product-approved examples. They are used elsewhere, so they do exist.
I have, somewhere in my possession, a table of typical signalling
equipment loads, which I will try to find and summarise on this group
next week. As far as LED signals are concerned, I believe that they
have a higher demand than bulb signals, owing to the large number of
individual LEDs as opposed to a single bulb.
Hope this is of further use.