"peter" wrote

And there was chaos in the evening too. I arrived at Kings X at abut
18:15, to catch the 18:27 to New Barnet. Onthe board it said 'On time'
until 18:29, when it disappeared, reappearing a few minutes
later as 'Delayed'. Eventually a platform was posted, and it departed at
around 19:00 (by which time the boards were advertising the 18:57 as 'On
Time')

There were no audible announcements made to the station concourse. The
explanation from the information desk was that trains were being diverted
from Moorgate, and this was causing congestion. But if this were true,
there should have been additional departures of these diverted trains on
their return journeys, and yet nothing was posted.

There was disruption again this morning (Wednesday). After travelling in
from Arsenal to KXStP with my daughter, I looked in at King's Cross and
noticed a very odd train on the main departure board - 0839 to Old Street
only. Closer inspection revealed that there was also an 0839 arrival from
Welwyn Garden City showing - perhaps the diverted 0758 WGC - Moorgate? I
assume someone had forgotten to delete the Old Street stop from the system,
which was thus expecting the train to continue there after King's Cross!

As I had time to kill before I could use my £6.65 Advance ticket home to
Retford, I decided to investigate what was happening. I took the Northern
Line to Old Street and joined a northbound FCC service which was waiting
there. After several minutes, it set off but took 20 minutes to Essex Road
and another 20 to Highbury and Islington, where I gave up!

In message , d
wrote:
Is there a case for extending
the 3rd rail to finsbury park

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.

--
Clive D.W. Feather | Home:
Mobile: +44 7973 377646 | Web: http://www.davros.org
Please reply to the Reply-To address, which is:

In message , Clive D. W. Feather
writes
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?
--
Clive

In article ,
(Clive) wrote:

In message , Clive D. W.
Feather writes
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?

They cope only with difficulty. In DC electrified areas AC track circuits
tend to be used to avoid interference and in AC electrified areas they
tend to use DC track circuits. As you can see there is no third way to use
in dual-electrified areas. I don't know if similar considerations apply to
axle counters.

--
Colin Rosenstiel

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:
Mobile: +44 7973 377646 | Web: http://www.davros.org
Please reply to the Reply-To address, which is:

In message ,
writes
They cope only with difficulty. In DC electrified areas AC track circuits
tend to be used to avoid interference and in AC electrified areas they
tend to use DC track circuits. As you can see there is no third way to use
in dual-electrified areas. I don't know if similar considerations apply to
axle counters.
I understand what you say, but surely there is a frequency that can be
used that isn't a harmonic of either the 25kV or the ripple on the dc?
--
Clive

In message , Clive D. W. Feather
writes
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.
Are you saying that traction current is the major problem when dealing
with the two different types (ac and dc)?
--
Clive

On Tue, 15 Feb 2011 15:14:08 -0600
wrote:
They cope only with difficulty. In DC electrified areas AC track circuits
tend to be used to avoid interference and in AC electrified areas they
tend to use DC track circuits. As you can see there is no third way to use
in dual-electrified areas. I don't know if similar considerations apply to
axle counters.

Given all the harmonics produced by modern electronic power systems on trains
surely most track circuits would be pretty well filtered anyway?

B2003

On Tue, 15 Feb 2011 22:05:39 +0000
"Clive D. W. Feather" wrote:
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

I didn't know that about 3rd rail, I assumed the rails were grounded. Doesn't
that mean that theres a potential risk of electrocution just from the running
rails?

B2003

wrote in message
...
On Tue, 15 Feb 2011 22:05:39 +0000
"Clive D. W. Feather" wrote:
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

I didn't know that about 3rd rail, I assumed the rails were grounded.
Doesn't
that mean that there's a potential risk of electrocution just from the
running
rails?

... and any exposed metalwork on a train. I believe this is one reason why
you won't find metalwork on a platform that's within reach of a train. Where
this is unavoidable the metalwork is bonded to the running rails. Richard
Catlow used to be the source of all knowledge about this subject.

--
DAS