Electrified railways in the UK have existed for well over a century and much has been written on the types of system and their voltages. The merits and downsides of overhead lines versus third rail, and DC versus AC, continue to be a topic of conversation when traction engineers meet both at seminars and social gatherings.
In contrast, the methods by which the traction current is controlled attract little attention, but without a robust system, the electrification would be unmanageable. Electric power is delivered to the railway from the national grid, although it was not unknown in earlier times for rail companies to build their own power stations. The method of distribution supply is very different for AC and DC systems, although both need periodic connections to national grid lines.
The architecture of AC electrification is simple. Feeder Stations are the grid in-feed locations where the high voltage grid is transformed to 25kV (or 50kV for the latest auto transformer systems) from the high voltage national grid at sites where pylon routes cross the railway. These are positioned about 40km apart and thus feed current for around 20km in each direction.
Where the ends of adjacent grid in-feeds meet, there is a neutral section, which is a very short piece of unpowered catenary. These prevent out-of-phase paralleling between grid supplies which would replicate fault conditions.
Track Sectioning Cabins (TSCs), positioned at feeder stations and intermediate locations, are where switching of the discrete electrical sections to individual catenaries can be implemented. Should a Feeder Station lose the grid in-feed, then emergency feeding arrangements can be put in place by extending the power from adjacent feeder stations, thus lengthening the feeder distance to around 40km.
Significant voltage regulation issues may occur at the extreme ends of the sections, and the voltage can drop to as low as 17kV. This is not a major problem unless rail traffic levels are high, when train regulation restrictions might have to be put in place.
A DC system, with its lower voltages, requires a more complicated arrangement. Since load current values are high, voltage regulation requirements dictate that feeder points have to be, typically, 5km apart. It would be operationally and commercially impractical to have grid connections at such short distances, so an AC network is provided by the railway to create an internal distribution network. The infrastructure owner thus owns a ‘mini grid’ supply to the substations where the power is rectified and DC current is fed to the overhead line or third rail.
On the extensive UK ex-Southern Region third-rail system in Kent, Sussex and Wessex, the AC network is predominantly at 33kV although, in remoter areas, it can be 22kV or 11kV. Power from the grid is obtained from around 40 supply locations with switching stations not always adjacent to a Network Rail site, maybe up to two kilometres distant.
The AC distribution cables are carried in trackside cable routes separate to any other lineside application, such as signalling. Each substation rectifies the AC voltage to DC, either at 1500V for overhead lines (Tyne & Wear Metro) or 750V for third rail. Nowadays, the equipment to do this is solid state but, in the past, rotary convertors and mercury arc rectifiers were used. Unlike AC, the DC electrical sections can be continuously connected and paralleling is used to assist power supply regulation. Between substations, Track Paralleling Huts (TPHs) are located that allow localised switching of power to different overhead catenaries or third rail tracks.
Controlling the power supply
For both AC and DC, the electrification system must be capable of being controlled from an Electrical Control Room (ECR). In the event of fault conditions such as a short circuit, automatic circuit breakers at the feeder station or substation(s) will trip to disconnect current from the catenary or third rail.
In an emergency, typically a person in danger of electrocution by being in contact with the catenary or third rail, the current may need to be switched off quickly and manual intervention from the ECR controller is required. The control room also undertakes routine planning and implements tasks such as isolations for maintenance work, monitoring the level of supply current and liaison with the national grid authorities for any prime source power problems.
Since electrification systems go back over a hundred years, many different technologies and practices for control of the electric current have emerged. On AC systems, the usual arrangement has been the provision of data links (known as ‘pilots’) from the ECR to the traction power locations. These low capacity data links are carried on telecom circuits provided by the S&T department.
The requirement for resilience is met by having A and B pilots routed in different cable or transmission systems in diverse routes. On occasions and for pragmatic reasons, it was known that the two pilots were borne on different cables within the same trough route but this was sub- standard practice.
On other legacy systems (typically the older DC network), the traction power sites use a separate cable transmission network provided entirely by the electrification and plant engineers. These are located in trough routes, separated from any high voltage feeders by different compartments and thus minimising the risk of mutual contact.
Thirteen ECRs currently exist at the following locations:
» AC lines – Romford, York (some DC), Rugby (some DC), Crewe, Cathcart; » DC lines – Lewisham, Selhurst, Raynes Park, Eastleigh, Brighton, Paddock Wood, Canterbury, Sandhills (for Merseyrail).
Strangely, the combining of ECRs with modern signalling power box locations never happened, maybe because departmental preferences compartmentalised the thinking. Network Rail is implementing a national SCADA (Supervisory Control and Data Acquisition) system that will integrate electrical control into the new Rail Operating Centres (ROCs). The main contractor for this project is Telent, which has a long pedigree of supplying railway telecommunications systems.
The goal is to create a single, unified electrification control network for the main line railways of Britain, but with a staged approach to match other electrification works. The majority of the thirteen existing ECR sites have control equipment that is becoming life-expired. The oldest systems still employ discrete switches and mechanical switchgear and even the earlier screen-based systems are obsolete. Spares are often difficult to obtain and familiarity with the ageing technology can be a problem.
Couple this with the new electrification projects – Great Western route modernisation (GWRM), Welsh valleys, Midland main line, North West, Trans-Pennine, Edinburgh to Glasgow – and a clear need has emerged to provide a unified means of control for both the existing and new sections of electrified railway. This is set out in the requirements of CP5 as a principle for new electrification schemes. It is also recognised that much of the remote equipment associated with the existing ECRs that control the AC lines is still relatively new and does not justify renewal at the present time.
The project is thus partly renewal- driven and partly to support new electrification deployment. The new control equipment will be installed, initially, at the existing ECR sites. There are nine ECRs that will retain their legacy remote equipment including the associated communications or pilots. Four ECRs on the DC network will require more significant works to provide both the new control network and the replacement of existing electro-mechanical switching equipment at 250 of the substations and TPH sites.
In time, a rationalisation of the existing ECRs will occur, with transfer of control to the ROCs. With the creation of a single resilient UK unified control platform, this transfer of control location will be made possible by the flexibility of the transmission architecture. Telent will undertake this work on behalf of Network Rail, including the electro-mechanical control replacement at the older sites on the DC lines.
The SCADA requirement
SCADA technology has been around for some time but application on a national scale within Network Rail has only become a practical proposition with the provision of the NRT (Network Rail Telecom) Fixed Telecom Network (FTN) and its associated fibre cabling and digital transmission systems. FTN is currently being upgraded to FTNx that embraces IP (Internet Protocol) addressing and technology. Within this will be structured a WAN ‘cloud’ for the SCADA project.
FTNx will have ‘points of presence’ and fibre connections at all the ROC and ECR sites. NRT provides access links on an ‘as required’ basis so, if fibre does not exist at places where a break-out point is required, then new fibre links, installed under a separate Network Rail contract, will be terminated, tested and integrated by Telent. The use of IP will also permit a voice facility to be superimposed upon the data network (VoIP – voice over Internet protocol), thus creating a virtual private telephone network for those needing to interface with ECR operations.
The SCADA project will have data centres at Manchester and Three Bridges ROC sites (two are needed to provide a resilient system) that will service the existing ECR sites using new control equipment together with screen based GUIs (Graphical User Interfaces) displaying all the external supply and switching locations. These will have two large screens showing the diagrammatic layout of the electrification system for the area plus two smaller screens detailing alarms, event logs, out of course occurrences and suchlike.
Controllers will be able to interrogate the screens to show the status of individual switching locations and thus open and close circuit breakers as required using a mouse control. Identical arrangements will be provided at the ROC sites as these come on stream as and when ECR operation transfers to these sites.
Not all ROCs yet control areas of electrified railway, for example Didcot, Cardiff and Derby, but these will have the same capability so that electrification projects will have a ‘natural home’ for control when the time comes. Since the WAN cloud is a single entity, it will be relatively easy to add or delete sites as electrification policy unfolds. Data rates will vary according to need but two 100Mbit/ sec links will connect the Three Bridges and Manchester data centres.
Progressing the project
Network Rail has been keen to adopt a systems engineering approach to establish both the technical configuration and the method of operation. This has involved consultation with subject matter experts from the end user community. With the many complex requirements of the project, one of the first steps made by Telent has been the building of a reference system at their Warwick premises. This enables both supplier and customer both to assist with the development of the design and integration and to have the ability to make adaptations and fully test them as and when necessary to suit local circumstances at particular sites.
The first area to be transferred will be the electrified Heathrow Express service currently under the control of Romford ECR. With GWRM electrification and Crossrail well underway, it makes sense to transfer this to Didcot (Thames Valley) ROC and this will happen in 2016 so as to be ready for the GWRM ‘power up’. No doubt there will be both technical and operational lessons to be learned as the new system is introduced, with the electrification controllers assisting the process of familiarisation, thus learning lessons for later sites.
After that, the first ECR site to be converted will be Romford, covering the whole of the Anglia electrified lines. Paddock Wood will follow, which will yield experience on the DC lines. Thereafter, a rolling programme will be implemented taking account of the progress of new electrification schemes and the condition of existing assets.
Safety and security
It must always be remembered that electrified railways carry both high voltages and large currents. Safety factors have always been a high priority and part of this project has been to fully assess the safety aspects. The existing configuration has very little over-arching control redundancy and, should an ECR be disabled, then no effective control of the network will exist other than to staff the individual feeder stations and switching locations.
The new SCADA system will enable dual redundancy across the entire network with the ability to control a disabled site from another location if a disaster was to happen. This is a major improvement as much needed resilience is provided. The requirement to quickly switch off power in an emergency will be assured by both the IP-based telephone service and improved links to the NRT Railtel (ETD – extension trunk dialling) phone network and the 17x emergency call numbers to the ECRs.
Pressure to give the SCADA system a SIL (Safety Integrity Level) rating has been robustly assessed to guard against the introduction of overstated and ultimately meaningless complications. The assessment has led to a SIL 0 designation that will be reviewed by Ricardo Rail (formerly Lloyd’s Register Rail) acting as the independent safety assessor.
Cyber security is another important consideration. The CPNI (Centre for Protection of National Infrastructure) has been consulted as the SCADA network falls into this category. The system has been designed and will be implemented with the CPNI guidelines for cyber security adopted and the system will be independently penetration-tested for potential security breaches. Encryption of the sensitive elements of the network is one such measure, another has been to security clear all Telent staff working on the project.
The Network Rail specification for the project includes some 6,000 requirements, many arising from a robust systems requirements review post contract award. Collaboration between Network Rail and Telent is pivotal for success but Network Rail has many other stakeholders needing to be consulted to attain the necessary approvals.
Telent has 95 people engaged on the project covering design engineering, system engineering, software development and system integration, with the majority based at its Warwick site while others undertake site installation work. The company is working with Network Rail to get the required telecom infrastructure in place and Cisco will supply the data equipment (routers and terminals) and associated software. Other suppliers working on the project are:
» Vitra for the supply of work station desks;
» Interfleet for the training of electrical control staff at the Three Bridges and Manchester sites;
» CCD for ergonomic considerations;
» CNS for cyber security;
» IP Trade for voice telephony.
The overall contract has a publicised value of £27 million but some variations to this are expected to cover changes in scope. The contract has been in existence since mid-2013 with a completion scheduled for the end of December 2017 for the basic network, by which time it is hoped that every main line electric train in the UK will be drawing traction current controlled by the new SCADA system.
This is a significant project with many inter- activities to other projects. Co-ordination and communication is thus an essential part. The end result will be a power supply network using the latest technology and standards that will be fit for purpose for decades to come. The new Network Rail SCADA system will provide the common national platform for the Digital Railway – SMART grid, leading the way for efficient use of energy and greater operational resilience.
Thanks to Scott Burt, Telent project director, for his time in explaining the project with all its ramifications, and to Saleem Mohammad, head of Network Rail’s national electrification programme, for his input.