The London and North Eastern Railway started to electrify the Shenfield to Liverpool Street line during the 1930s; civil engineering work had started before the Second World War but the conflict delayed completion till 1949. The electrification system was 1,500 volts DC, which had been the standard at the time. However, British Railways switched the line to 25kV AC, its new standard, in November 1960.
The converted system continued to give service for many years but, as a fixed tension system, it was very vulnerable to temperature changes – the contact wire could sag severely at high temperatures, resulting in speed restrictions and severe capacity reduction in hot weather.
The system would also be under excessive stress in cold weather leading to failures and poor current collection performance. As the configuration was that of ‘compound equipment’ (with a third conductor in the contact system), the installation was heavy and slow to work on, parts were scarce and expensive, and catastrophic and complex failure modes were regularly experienced – the DC arrangement was designed before modern section insulators.
Essential upgrade
In the 21st century, the decision was made that the existing converted system was no longer fit for purpose and designs were drawn up to install modern overhead line equipment (OLE).
The philosophy behind the renewal programme was far reaching. The new arrangements were to include full mechanical independence, with registration arranged so that each wire would have its own individual catenary support and registration arm with knuckles removed.
A further characteristic, which would befit complex sites such as Forest Gate, would be to segregate main line and crossover wire runs with crossover wire runs to cover one pair of tracks only, where practicable.
As a final contribution to reliability, the new design would remove multi-track spanwire registrations and section insulators would be removed and replaced with overlaps where practicable.
Rather than traditional tensioning devices, in the form of balance weights, the new installation incorporates automatic tensioning equipment in the form of Pfisterer’s Tensorex spring tensioning system. This allows suitable contact system performance to be maintained within a normal range of temperatures and requires minimal maintenance compared with the balance weight system.
The contact system performs with near constant tension and there is no need to run cross-track wires, nor is there a need to build additional masts to support weights on an A frame.
It is worth noting that the system has been proven in Switzerland for approximately 15 years with, reportedly, zero failures.
Introducing GEFF
The system developed for the Great Eastern conversion was designed by Furrer+Frey, which has been involved with the general works for more than ten years. The generic name for the system is ‘GEFF’ and the Network Rail certificate of acceptance for the design was issued in 2012.
The conversion is technically an extremely challenging programme of works due to the complexity of the existing infrastructure and its interface with the operational railway. In total, 345 wire runs and associated structures for a new auto-tensioned overhead line system are to be installed.
In summary, the Furrer+Frey design delivers enhanced electrical clearance, reduced wind loading and mechanical simplicity. Structural life costs will be reduced and even future renewal will be simplified. In addition, the new configuration results in improved signal sighting – a welcome bonus on such a busy piece of railway. There is easier adjustability/repair and the equipment is faster and safer to work on.
Progress has been maintained on the system renewal and only a relatively small part of the system remains to be completed. There has already been a significant improvement in OLE performance with a reduction in faults and service disruptions – there has been a direct correlation between wire runs renewed and a reduction in delay minutes.
Coupled with the contact system it is the question of structures and foundations. Replacements have been built to recent Eurocodes with a standard choice of side-bearing concrete foundations and a generic range of tubular piles. However, there have been a high proportion of custom foundations due to inner London build constraints, with examples being gravity pads, piles and special shapes.
Christmas at Forest Gate
One of the areas still to be completed was the strategic junction at Forest Gate on the Great Eastern main line. At this junction, the multi-track main line is joined by the route from Barking which also continues over over the main line on a bridge. Thus the site is complex and strategically important to the reliable running of the Great Eastern services, with the potential for any problems to cause major delays for the travelling public.
James Hill of Network Rail described the works and emphasised that, due to the nature of the normal intense service through the site, the works were planned to be undertaken in a ten day Christmas blockade between the twenty third of December 2018 and the second of January 2019. Under the management of Network Rail Infrastructure Projects, with design by Furrer+Frey, contractors and plant were mobilised and site work commenced following the last services before Christmas.
The opportunity had been taken to ensure robust preparation for the works and, as well as materials management issues, a small number of electrification structures were replaced before the blockade. The construction main contractor was Network Rail’s OCR team while stage work design was supported by OLE Limited at Derby, which also provided site design support; essential to ensure that, where adjustments were required to preconstruction approved design, in the light of emerging physical situations, the installation complied with required design standards.
James mentioned that some structures were reused where the positioning was suitable and that the new GEFF design allowed quantified choices to be made. The new equipment weighs approximately 50 per cent of the original DC equipment and the radial and wind loads are also less than the earlier DC installations.
GEFF anchor loads are also around 60 per cent of those for DC, so, in theory, all of the old structures can be reused. Furthermore, there are generic decisions still to be made regarding crossovers and, as that is the nature of the Forest Gate situation, those choices came into play. The old DC equipment is heavy with low uplift and high rise and fall, whereas the GEFF is light with a higher uplift and no rise and fall. So, the design had to be assessed with this in mind.
The decision was made to undertake as much preparation and pre-build as possible, aiming for 90 per cent preparation prior to wiring. However, germane to the preparation planning process were the drivers that, when compared to the older DC installations, GEFF cannot carry some high ex-DC radial loads, the catenary height is lower, the contact height is different and catenary sag is considerably less. A hybrid installation philosophy was therefore carried out during preparation works, leading to reduced in-possession time when finishing off.
Project support
Across the total Great Eastern renewal scheme CPMS (Collaborative Project Management Services) has been active in a project support role. CPMS has successfully supplied the client with a full project delivery solution including programme, project delivery, planning, document control, engineering, procurement and commercial management services. It has also developed and successfully discharged a principal contractor competency on behalf of the client.
Mat Baine of CPMS explained that his organisation has an extensive team of engineering and construction industry experts and delivers on-the-ground construction works, backed by full RISQS accreditation. He emphasised that work does not end once construction is complete, follow-up was by an experienced and efficient ‘entry into service and handback’ team.
In order to support the project, CPMS worked directly for clients and third parties progressing alongside the railway. The company’s railway experience helped to translate and ease the path towards the successful delivery which was achieved at the rewiring site.
Of great value was the recognition of the benefits of a close collaboration between engineering and construction throughout a project’s lifecycle. Expert and early involvement during development helped to incorporate value engineering and streamline buildability into the scheme.
A culture of ‘safety first’ has been effectively embedded on the whole project along with the implementation of a full suite of project controls, including schedule adherence, unit cost modelling and KPI reporting metrics. Across the programme, to date, the delivery solution provided by CPMS has been seen to generate efficiency improvements of 25 per cent for the client.
Successful conclusion
The Christmas work at Forest gate has benefitted from a focus on instigating a significant change in the safety performance of the GE project. Starting with a focus on getting the basics right through to seeking new and innovative ways to deliver the works in a safer, more efficient manner, CPMS has worked with the supply chain and site operatives to understand and improve how the project is delivered. A measure of the success has been a new and highly targeted safety campaign, CPMS has increased the volume of close call reporting on the GE project by over 300 per cent.
All of these measures have been successfully implemented to bring safety to the forefront, culminating in the effective performance in the delivery of the Forest Gate works.
Central to the planning, accompanied by the vital materials and plant management task, was that, to achieve renewal, it was necessary to remove and replace nine wire runs with severely restricted staging options. James explained that works were purely OLE related with no permanent way remodelling. The track layout, however, is complex, with four crossovers in the junction configuration.
In all, some twelve and a half kilometres of overhead contact system were replaced during the planned blockade and normal services resumed, as planned, on the second of January.
This heavily trafficked piece of railway will assume even greater significance when the existing services are joined by the full Crossrail service when the route will be upgraded to an auto transformer 25-0-25 kV system; passive provision having been created at Forest Gate during the works.
With Forest Gate complete, there is now a continuous section of auto-tensioned GEFF OLE on the electric lines from the country end of Stratford station to Chelmsford, a distance of 42km. There remains only one major section of renewal to undertake, in the very complex Stratford area. Once that has been finished, the Great Eastern Route will be able to deliver massively improved reliability in all weathers, for the advantage of railway customers.
All in all, it adds up to a successful near-conclusion to a complex project.
There appears to be an inaccuracy in the first paragraph, the Shenfield-London lines were not switched to 25000acv in November 1960. I seem to remember that the ex 1500dcv lines were only 6250acv due to the original insulators not being fit for 25000 acv. This situation continued until the insulators were renewed in perhaps the 1990s. For clarity, I believe the Colchester-Clacton line was the test-bed for 25000acv in the early 1960s. I’m sure others may better know the exact dates.