Siemens inclined OLE

The cost of electrification significantly constrains the expansion of the UK’s electrified railway network. Rail Engineer has reported on various worthwhile initiatives to reduce the cost of electrification as, for example, in our ‘Making electrification affordable’ feature in Issue 106 (May/June 2022).

In this issue we are pleased to report on one that has the potential to reduce the number of masts required by between 24% and 35% depending on the curvature of the line. Siemens calculates mast savings on the straight Hull to Selby line to be 35%. As shown below, on the more curvy Perth to Aberdeen route, mast savings are 24%. This innovation is the Siemens Sicat SX system which in April received National Technical Specification Notices (NTSN) design certification for use in the UK.

Sicat (Siemens Catenary) OLE systems have been in use in the UK for both DC and AC systems. The 2002 Tyne and Wear metro extension uses Sicat LD, whilst the 2005 electrification of the new Larkhall branch used Sicat SA. In 2019, Sicat SA cantilevers were included in Network Rail’s UK Master Series (UKMS) of approved OLE design ranges.

The development of Sicat SX began in 2004 when Hungarian State Railways won EU funding for an initiative to develop lower cost electrification. In 2010, this resulted in a 4km section of the 90km line between Bajánsenye and Boba in western Hungary being electrified with the novel Siemens SX system. Compared with conventional Hungarian electrification, this saw an increase in span length on straight track from 75 to 99 metres and on track with a 1,000-metre radius curve from 61 to 73 metres.

In all OLE systems, the contact wire has a zig-zag path, or stagger, to avoid wearing a groove into the pantograph. Generally, the catenary wire, which supports the contact wire, has the same stagger as it is vertically above it. With Sicat SX, the catenary wire’s stagger opposes the contact wire’s stagger so that the droppers between these two wires are inclined. Combined with increased catenary wire tension and a novel choice of conductors, this arrangement provides an OLE system with a lower deflection in high winds and so offers longer spans.

Further refinement of the Sicat SX design saw the permissible span length increased to 112 metres when the system was chosen for a rolling programme to electrify the remainder of the Danish network. This work is being undertaken by a consortium of Siemens and Per Aarsleff AS and started in 2015. By 2026, this alliance will have electrified 1,364 single track kilometres.

System overview

To learn more, Rail Engineer visited Siemens Mobility’s Glasgow office to talk to Peter Pick, principal project engineer, electrification and Eliot Clark, principal design engineer, electrification, whose enthusiasm for the Sicat SX system was evident.

Peter noted that Sicat SX uses the same set of service-proved components as those of the Sicat SA system. The only difference is that for conventional systems the catenary clamp on the cantilever’s horizontal beam is vertically above the registration arm’s contact wire clip, whereas on the SX system the catenary wire is generally not directly above the contact wire.

Eliot explained how the Sicat SX system’s catenary and contact wires are both quite different from those on conventional OLE. It is, for example, more accurate to describe its catenary wire as a cable as this has a core of seven aluminium coated steel wires cables inside an external sheaf of 12 aluminium wires giving it an external diameter of 15mm. Such cables, as specified in European Standard EN 50182, are extensively used for European HV transmission lines and are rated for a maximum tension of 90kN. In the Sicat SX system, they are tensioned at 30kN.

The contract wire of the Sicat SX system has half the tension of the catenary cable, i.e. 15kN. This has an 80mm2 cross section and is a Copper alloy with 0.5% Magnesium content to increase its life. In comparison, Network Rail’s OLE systems typically use contact wires of 107mm2 and 120mm2. Using an 80mm2 contact wire instead of a 107mm2 wire saves 206kg of copper per kilometre. With the reduced use of copper, Sicat SX’s catenary/contact wire system offers a 50% cost saving for conductors over traditional catenary/contact wire systems.

He also noted that despite using less copper this also offers an impedance that is about 10% lower than the current UKMS125 systems which, if Sicat SX were to be widely installed, would offer electricity cost savings of the order of £1 million per annum.

With much longer spans Sicat SX offers tension lengths up to 2,000 metres with fewer tensioning devices and associated anchor structures. With longer tension lengths, it also offers two, rather than three span overlaps. Sicat SX is designed to operate in a temperature range of -30°C to +50°C, compared with the UK standard of -18°C to +40°C. Hence, if Sicat SX’s temperature range was designed for the UK standard it would be possible to further increase maximum tension lengths.

A further advantage is that Sicat SX offers a one-metre reduction in mast height to reduce cost and visual impact. This is because it uses a standard cantilever rather than the inverted cantilever most commonly used by the UKMS.

Low bridges

In Peter’s experience, low bridges in Denmark were invariably demolished or rebuilt as part of the electrification. This differs from UK practice where the emphasis seems to be to avoid bridge rebuilds wherever possible, without taking full account of whole life costs given the future maintenance and reliability challenges of bridges with minimal OLE clearance.

Hence the complexities of getting a 25kV OLE system underneath a bridge with such minimal clearances have not been an issue in Denmark. In the UK, surge arrestors with insulated coatings have enabled clearance between the OLE and the bridge underdeck to be reduced to 40mm as in the case of the Cardiff Intersection bridge.

This requires the OLE system height under the bridge to be zero. This is done using a twin contact arrangement where the contact wire is spliced into the catenary and brought down so that it is side-by-side with the contact wire.

For the Sicat SX system that has its catenary cable at twice the tension of the contact wire, this was a potentially problematic issue which had to be resolved before the system could be approved for use in the UK. The solution, however, was relatively straightforward. Before and after the bridge there are splitter plates that separate the catenary into two separate contact wires each of which has a tension of 15kN. Thus, under low clearance bridges Sicat SX has three contact wires side by side.

Aberdeen case study

Electrification of the 148 route km between Perth and Aberdeen is a significant part of the Scottish Government’s railway electrification programme. To assess the benefits of electrifying this route with the Sicat SX system, Siemens considered the circa 5,000 masts that would be required using both Sicat SX and the conventional UKMS. This analysis took account of line curvature, how bridges and structures determined mast positions, and OLE wind loading as required by NR/L2/CIV/072.

This work demonstrated that using Sicat SX would reduce the number of masts required by 24% and the number of tension lengths by 25%. With Sicat SX, the average span length is 67 metres which is 32% greater than the 50.9 metre span length of UKMS (these are indicative figures assuming double masts for the entire route). As well as offering large cost savings, this also offers significant delivery benefits as with Sicat SX there would be a significant reduction in the possessions required to install foundations and masts between Perth and Aberdeen.

Siemens estimates that the use of Sicat would reduce the amount of steel required from 7,669 to 5,234 tonnes and the amount of concrete required from 12,973 to 11,439 tonnes, which would reduce the embodied carbon footprint from 14,705 to 11,468 tonnes of CO2E. In addition, fewer OLE masts will reduce future maintenance costs.

It is now seven years since the Government cancelled the Midland Main Line electrification and cut back due to the cost of the Great Western Electrification Programme (GWEP) as a result of GWEP’s costs rising from £874 million to £3.8 billion for the cut-back scheme. At the time, the Government had lost faith in the industry to deliver electrification at a reasonable cost and also decided that electrification was the wrong technology.

Since then, much has been done both to make the case for electrification and win back trust by showing how electrification can be delivered in a cost-effective manner. Sicat SX is a further example of what can be done to reduce electrification costs and so improve the business case for electrification. Now that it has achieved NTSN design certification, Rail Engineer looks forward to seeing its inclined electrification in the UK soon.

Image credit: Siemens Mobility