Operational communications are important in supporting both signalling and power control on any railway but, for a major city metro line, the need becomes ever more essential. The communications systems are there to monitor the safe state of the infrastructure and to be the means of controlling the activities and movement of staff and customers in any emergency situation.

In short, such systems are vital and have to be available on a 24/7 basis. So when an existing system has to be replaced by a more modern technology, without disruption to service, one begins to get a feel for the challenge of the task.

This is exactly the scenario that has been taking place on the London Underground Central line during a recent upgrade. Rail Engineer went to visit the line’s control room in West London, to see what was involved and to meet with the system supplier and the control room staff.

Communications Control System (CCS)

The Central line extends from Ealing Broadway and West Ruislip in the west to Epping and the Hainault loop in the east. There are 47 stations with 12 major interchanges to other lines and around 50% of the route in deep level tube tunnel. The line has operated in ATO (Automatic Train Operation) mode since 1994, this system being supplied by Westinghouse.

The CCS provides connectivity with the CCTV and public address systems on all stations, the operational and LU telephone networks, the emergency traction discharge system (ETCDS) to shut off power and alarm monitoring from equipment rooms and stations. All this requires a dedicated transmission and telephone exchange network with recording equipment for both voice calls and limited video capture.

Providing a replacement system was entrusted to Sella Controls (formerly Hima Sella). The project is termed a ‘brownfield’ challenge, meaning that all facilities have to be kept in operation, the new control system has to interface with existing equipment at stations and in tunnels, all while retaining the transmission bandwidth obtained from the LU ‘Connect’ network. Not an easy assignment, with lots of opportunities for things to be misunderstood with consequent variation to requirements.

Another challenge was the human-machine interface (HMI) – in short, the operational workstation screens. Because the change from old to new would be a gradual process, the layout and operation of the screens needed to be kept essentially similar. This meant that a lot of the features normally available as standard in a ‘greenfield’ project (i.e. a completely new control room) could not be incorporated in the way the supplier would like and either had to be abandoned in the short term or formatted in a different way. In consequence, much bespoke adaptation was needed, this being one of Sella Controls’ strengths.

It should be noted that the CCS is there for the operation of the railway and not communicating with the travelling public. Thus, help points, information displays, routine public address announcements and public accessible telephones are handled by station-based systems.

Control centre equipment

The Control Room has 11 workstations for the control room staff and the duty engineers, all of which have access to the CCS screens. There is also a twelfth workstation located at a separate back up installation. The CCS has two central systems (A and B) within the communications equipment room (CER), each feeding the operational workstations. This gives the necessary redundancy which ensures continued operation in the event of any CCS equipment problem.

Each CCS system has, at its heart, two Amplicom servers, the company hand-building its products to Sella Controls specification. These are different to the many servers produced for the mass market in that they are intended for a 15-year service life as against the typical five years for normal commercial usage.

A prime role within the CCS is the monitoring of sub-system alarms, to diagnose the implications, to decide on the urgency and to direct any fault investigation and fault rectification. So often in alarm monitoring presentations, these just appear as a status list of equipment conditions with a red or green marker to indicate whether the equipment is in good order or failed. This is not always very helpful and can result in technicians being despatched to site without any real knowledge as to the seriousness of the problem.

In the new CCS, the screen alarm can be ‘drilled down’ to establish the precise nature of the alarm condition and to show a graphic of the particular card with its LED status. Thus any technician is made aware of where the fault may lie and the precise piece of equipment to be investigated for re-set or change out.

Whilst aiming to mirror the original workstation screen layout and functionality, the diagnostic terminal in the equipment room, which gives an overview of all the station systems, was viewed by one of the duty engineers. Recognising the value of this screen, similar units have now been installed in the control room to assist the controllers in establishing a first analysis of the problem when an alarm is received from anywhere on the line.

The control room has to cope with an inevitable turnover of staff and the consequential training of replacement controllers. To do this on the live system is impractical, so a separate training room is provided in an adjacent office. The workstation layout is identical to the real thing but with the ability for the trainer to simulate typical situations that might arise, including some challenging faults.

Exchange network

The core of the CCS is the central exchange unit and 19 smaller linked exchanges at the signalling interlocking sites throughout the line. The exchanges, known as Dikos units, are provided by Funkwerk, a German company which has a close liaison with Sella Controls. These replace an earlier Dikos unit (model 210) with the current 310 series that has more capacity and a faster processing speed.

As for the control room servers, these exchanges are industrial quality and intended for an extended service life of around 15 years – the previous units achieving 20 years.

Operational telephones of various types and specification throughout the Central line (mainly ISDN models) are connected to one or other of the exchanges. This is a self-contained network, kept separate from the general-purpose LU telecoms facilities, so as not to experience any busy conditions if an emergency occurs. Tie lines do enable access to the LU network, but connection to external lines out into the wider world is barred. All voice calls are recorded using NICE recorders.

Tunnel telephones and power control

The traditional London Underground system for tube drivers to speak with control, by means of clipping a telephone on to a pair of exposed copper wires fixed to the tunnel wall at cab height, has been superseded by the advent of the Connect Tetra radio network.

Whilst partly replaced by fixed telephones located on tunnel headwalls, the two copper wires are retained for their other purpose of getting the traction power switched off in an emergency, achieved by shorting the two wires together or by clipping on a ‘shorting’ connection. The electric traction power control is immediately alerted to this condition and sets in motion, via the CCS, an investigation as to what has occurred.

As the duty engineer remarked: “It is easy enough to get the power off but quite complicated to get it switched on again.”

The tripwire system is segmented into 16 sections for the whole of the Central line. Part of the new CCS project has been the provision of an interlock between the control room equipment and the power controllers (located elsewhere) that prevents power being restored until the CCS controllers are satisfied it is safe to do so. This will involve establishing the cause of the trip, ensuring that no one is touching or adjacent to the conductor rails, and confirming that any fault causation has been rectified. Only then will the release be made to the traction control room to re-energise.

CCTV monitoring

Many hundreds of cameras exist on the Central line to observe and monitor passenger movements, overcrowding, unforeseen incidents and suchlike. At Bank station alone, there are over 380 cameras to view all the platforms, interchange passages, escalators, ticket offices and public areas. Smaller stations will have, typically, around 12 cameras with several hundred cameras being needed to cover the entire line.

Viewing and recording all the images is a logistical challenge and well beyond the resource capability of the CCS controllers. Monitoring and recording the day-to-day images is done at the individual stations, some of these being grouped together into clusters, where local staff have the knowledge and expertise to deal with typical daily situations.

If, however, any incident or emergency occurs, the CCS system can call up the appropriate cameras to observe the conditions and commence recording the images. Any equipment room intruder alarm will automatically switch on the camera for that location. The CCS control is primarily interested in safety situations, so station platforms where overcrowding is a regular problem will be reviewed more frequently than, say, ticket halls.

Under the CCS contract, the existing CCTV cameras were not replaced, these being mainly analogue from a variety of suppliers. Sella Controls had to ensure that all these camera outputs could be successfully transmitted via analogue to digital converters and the LU transmission network to the Central line control room with the appropriate level of resilience and quality.

One limitation of having to mimic the existing HMI has been the restricted number of images that can be portrayed simultaneously. Originally this was limited to two, but subsequent negotiation and adaptation has allowed this to be increased.

Transmitting the information

London Underground has a self-contained fibre-based digital transmission network known as Connect, provided by Thales under a design, install, and maintain arrangement. Used initially to support the new Tetra radio network, the network’s huge bandwidth is available for other applications, including the CCS.

Connect is arranged in a number of resilient rings and CCS makes use of five of them. Station equipment is connected via appropriate interfaces to a particular ring, each having a termination in the control centre equipment room. Any ring breakage will not impact on service, as communications traffic will be routed the other way.

However, to increase resilience, additional digital transmission links have been installed to connect rings together at a convenient out-station location, sometimes allowing station telecom equipment to be directly connected to these links, thus giving a quadruple path back to the control.

Commissioning and maintenance

From contract award in 2011, the new CCS was fully commissioned in July 2016. As is customary with brownfield projects, a continuing dialogue was required between contractor and client to ensure that system design and deliverables were in line with the customer expectations, necessitating a number of design changes along the way. Sella Controls provided maintenance cover for the 18-month period since commissioning. This ceased in January 2018, whence Telent (which has a general maintenance contract for telecommunications equipment on LU) took over the front line maintenance activities.

Sella Controls retains a second line support role as well as training Telent technicians on the structure and equipment configuration of the CCS.

Whilst the CCS system is very reliable, processes are in place to acknowledge any failure within 60 minutes of its occurrence and, if second line attention is needed, Sella has to respond within four hours plus a 48-hour limit to fix the problem. If this requires a software modification, often this will be achieved via a temporary patch, giving time for a fully tested permanent solution to be progressed.

As to the future, TfL’s vision is for an all-London telecoms network to support its transport operations. As well as the Underground, this will include the bus network, DLR, bike hire and other transport-related activities. When and how this will happen remains to be seen, but it is likely that existing telecom networks will be absorbed into the new vision, interfacing and adapting to a high-level management system to avoid wholesale replacement. Rail Engineer will watch developments.

Thanks to Transport for London and to Chris Elliott and Adrian Martin from Sella Controls for facilitating the visit


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