Proceedings 2002/2003 - IRSE

56
SIGNALLING CONTROL CENTRES TODAY AND TOMORROW
Signalling Centre Remote Interlocking Type of Relay Interlocking
Ashford Maidstone (indications only)
Sandhills Rock Ferry route relay free wired interlocking with electronic route setting
equipment (ERSE) entrance-exit panel
Tyneside Pelaw route relay free wired interlocking with entrance-exit panel
Yoker Craigendoran Scottish Region geographical relay interlocking with entranceexit
panel
York Church Fenton non-route-setting relay interlocking with individual function
switch panel
Colton Junction route relay free wired interlocking with entrance-exit panel
Hambleton
route relay free wired interlocking with entrance-exit panel
Marsh Lane
non-route-setting relay interlocking with individual function
switch panel
Neville Hill
non-route-setting relay interlocking with individual function
switch panel
Peckfield
route relay interlocking with a turn-push panel
South Kirkby
non-route-setting relay interlocking with individual function
switch panel
Stourton
route relay free wired interlocking with entrance-exit panel
Temple Hirst
route relay free wired interlocking with entrance-exit panel
Wakefield Westgate non-route-setting relay interlocking with individual function
switch panel
York North
relay controlled automatic signals on plain line
Figure 5: IECCs interfaced to relay interlockings
railway” memory for onward reporting to other IECC
sub-systems.
This approach has been very successful and has
allowed standard hardware and software to be used
to interface to several types of relay interlocking by
adapting the SSI geographic data to suit (see Figure
5). The early applications of RII were on a small scale
with typically one modest sized modern relay interlocking
incorporated in an otherwise all-SSI area.
The recent Leeds First project has used RII on a
much larger scale, and incorporates some quite
elderly non-route-setting interlockings as well as
more recent designs. Where necessary functions are
missing from the existing relay interlockings, a
careful safety analysis is required to decide whether
it is acceptable to provide these by additional logic
in the RII. It would be possible to implement a
complete interlocking in RII, but this would not be
acceptable as the hardware and software are not
designed and validated to SIL 4 safety integrity level.
An example of this was at the Neville Hill interlocking
outside Leeds, where it was necessary to provide
train operated route release and additional opposing
route locking before ARS could be used in this area.
The safety analysis concluded that implementation
of train operated route release in the RII was acceptable,
but the additional opposing route locking
required a modification to the relay interlocking
circuits.
SPAD MONITOR
IECC has always provided a comprehensive track
circuit monitoring function which warns the signaller
of unusual sequences of track circuit operation,
such as may be caused by track circuit faults, trains
dividing or SPADs. This monitoring function is very
effective in operation and can easily be configured
using data to handle even the most complex cases.
However, all alarms were reported as either
unexpected occupations or unexpected clearances
of track circuits, with no indication of the likely
cause. An additional opportunity for improvement,
which was highlighted in Lord Cullen’s report into
the Ladbroke Grove accident, is the provision of a
specific distinctive alarm to the signaller if a SPAD
occurs. This will ensure that actions to prevent an
accident, or at least to minimise its severity, are
performed without delay.
To implement the accident enquiry recommendation
as rapidly as possible, a stand-alone
PC-based SPAD Monitor sub-system (PSM) was
developed and rolled out to all the IECC sites. The
PSM is interfaced to the existing IECC via the
existing data link provided to connect ARS to a tape
logger. This gives access to all changes of signalling
state from both SSI and relay interlockings, plus train
describer steps and various IECC status reports.
The PSM logs this information on its hard disc,
allowing the obsolete tape logger to be removed,
and analyses sequences of track circuit and signal
state changes to identify any train movement which
should be classified as a SPAD. By combining this
with the train describer information, the system can
report the location of a suspected SPAD and the
headcode of the train concerned. To avoid any
changes to the IECC screens, this information is
displayed to the signaller on an additional small LED
matrix screen mounted at a suitable location on the
existing workstation (Figure 6). A distinctive audible
alarm is provided, together with an alarm cancellation
button and an override facility to avoid repeated
alarms during engineering work 3 .
The stand-alone PSM is only intended as a
temporary solution, and an enhanced SPAD alarm
function it is now being integrated into the signaller's