In message , Clive
wrote:
There are a lot of complex electrical issues with dual-electrified
track. It isn't just a matter of sticking down some third rail,
particularly since in this case you'd be extending those issues to the
main ECML tracks as well. I'd expect fixing them to cost at least 5
million pounds based on current signalling prices. If this sort of
problem is rare, it's not going to be economically justifiable.
Surely the equipment already exists that can cope with signalling in
dual (25kV & 750V) areas, why so expensive? Or are there other issues?

The equipment exists, *but it isn't in place*. In effect, if you wanted
to dual-electrify the lines from Drayton Park to Finsbury Park, you've
got to resignal that entire section of the ECML (four running lines, two
goods lines, two tracks to Drayton Park, and two to Canonbury). And with
relatively expensive kit. Hence the cost.

From memory, that area is signalled with DC track circuits. Obviously
you can't use these if there's lots of DC floating around in the running
rails. So you need immunised track circuits instead. Similarly you can't
use simple DC for signal control relays because of the risk of induced
currents.

Some years ago there was a very good post on uk.railway explaining some
of this. For example, third rail running rails need to be isolated from
earth to keep stray voltages away from underground pipes, but 25kV AC
running rails need to be grounded. Dealing with the interface is, um,
interesting.

--
Clive D.W. Feather | Home:
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