Guest writer: Danny Aisthorpe
With the need to electrify significant parts of Great Britain’s rail network to meet rail decarbonisation targets, the industry continues to design and develop innovative solutions that will deliver improved value over the life cycle of an asset.
One such solution, Siemens Mobility’s Sicat SA cantilever, has received acceptance from Network Rail’s Contact Systems Group and so is now included in Network Rail’s UK Master Series (UKMS). UKMS is a standard set of Overhead Line Equipment (OLE) design ranges for use on new and refurbishment schemes on Britain’s rail network.
The light-weight, aluminium Sicat SA platform offers cost, installation and maintenance advantages, having been designed with a focus on ‘value creation’ to address the challenge that the industry has been given to reduce the cost of electrification schemes and optimise their efficiency through the adoption of alternative technologies and processes.
Demonstrating the advantages
Siemens was able to demonstrate the benefits of Sicat SA through its work on the TransPennine Route Upgrade (TRU) project through evalutaion and dynamic testing processes. Working alongside design consultancy TSP Projects and key alliance partners to deliver a number of value-engineering work streams to demonstrate the benefits of including elements of the Sicat SA design range solution into the UKMS.
One of the main perceived advantages of the traditional UKMS equipment (which covers line speeds up to 125mph) is its modular construction. However, system procurement is often left until the later stages of the design process – thereby restricting the opportunity for any design flexibility. In contrast, the Sicat cantilever arrangement can be designed and readily fabricated specifically to suit the requirements of each site and so optimise performance.
The components for each style of cantilever are largely common throughout the Sicat range and can therefore be bulk ordered, even at outline design development phase. This not only gives greater assurance in achieving programme delivery targets, but also provides the flexibility to meet any programme changes. As the Sicat cantilever assembly is fabricated from lightweight aluminium tubing and aluminium components, the system offers an effective balance between adjustability, ease of fabrication, and ease of installation.
Using like-for-like system parameters, most UKMS cantilevers require a top mast bracket to be positioned 1.1 metres higher than is required for a Sicat SA cantilever, generating a saving in material cost. As a result, initial estimates show that the required section of steelwork can be reduced, representing a 25 per cent reduction in cross-sectional areas, and therefore further saving in material costs.
One of the key differences between the Sicat SA and UKMS OLE equipment is the weight of the support assemblies, with Sicat’s cantilever and brackets being 28 per cent lighter and the under-portal cantilever 35 per cent lighter.
At portal locations, there is also a significant difference in weight associated with steelwork to support the assemblies, such that an additional machine with a crane arm is required to install UKMS safely and efficiently – whereas Sicat SA support steelwork can be safely installed from the basket of a mobile elevated work platform (MEWP).
These savings in plant and installation time, together with safer manhandling at height (compared to that of heavier cantilevers), provide significant cost savings. The system may also be constructed either on or off-site, offering further potential cost, operational and safety benefits.
As well as new ‘green field’ electrification schemes, the Sicat SA cantilever can be used as a direct replacement for life expired or damaged equipment on existing routes and is compatible with existing MkI, MkII and MkIII overhead line systems cantilever assemblies. Therefore, when used in areas of existing electrification, the reduced load of the Sicat cantilever increases the probability that existing masts may be re-used, with resultant cost savings.
To identify the optimum solution for each individual project, Siemens is able to carry out dynamic modelling of the interaction between the overhead line contact system and different rolling-stock pantographs. This allows OLE designs to be fully optimised; for example, using parameters derived from both UKMS and Sicat for open route and discreet features, with various pantograph and speed combinations.
The TRU project has focused on value-engineering workstreams in support of the Railway Industry Association’s Cost of Electrification challenge. The project team utilised Siemens’ OLE dynamic software modelling tool to optimise overhead line parameters. Using this approach, the project identified that TSI dynamic performance criteria could be met with increased span lengths and is in the process of updating the Master Series to allow spans of up to 74 metres.
Longer span lengths can significantly reduce the number of foundations, structures and cantilevers required, as well as the associated equipment, resulting in significant cost reductions due to reduced infrastructure, faster installation, reduced overall time on site and significantly reduced waste and materials surplus.
An early incarnation of the Sicat SA overhead line system has been in operation in Scotland for more than 10 years, having replaced the life expired OLE equipment on the 6.5-mile Glasgow Shields junction to Paisley Gilmour Street line. More than ten years on, the equipment continues to deliver outstanding service, with exceptional reliability, availability and maintainability (RAM) scores achieved on this suburban route.
Catering for a large number of multiple pantographs, the route called for high availability and robust, long-life performance. Sicat SA has delivered this, providing assurance that, over the system’s life, it can meet both operational and environmental requirements, delivering reliability and therefore high availability.
Clearances and surge arrestors
Digitalisation enables transport operators worldwide to increase value sustainably over the entire lifecycle, with one such solution being Siemens 25kV surge arrestor.
The cost of electrification programmes is often adversely affected by the inevitable proximity between live overhead-line conductors and trackside structures. As the overhead line system is energised at 25 thousand volts, compliant electrical clearance must be allowed at both design and installation stages to ensure the electrification infrastructure doesn’t suffer unnecessary flashovers between live conductors and lineside structures.
The required electrical clearances are defined within legislation and standards. These control the design and installation requirements and allow for a number of ‘worst case’ conditions, including, for example, environmental conditions and pantograph uplift.
Clearances are an essential factor in the planning phase of overhead line system design. If a conflict of electrical clearances occurs, then considerations have to be made to either modify the relevant structure (bridge, tunnel or building) or lower the tracks, both of which require complicated, extensive and expensive design and construction works to achieve the required electrical clearance.
To address this issue, and so to reduce or eliminate the costs of either having to make modifications to the structure or to lower the track, Siemens has developed an alternative solution which uses a surge arrester in circuit with the overhead line system. This offers significant benefits both in terms of the cost and speed of electrification works, particularly compared to any requirement for reconstructing or modifying buildings, bridges or tunnels, or for lowering existing tracks.
By introducing a surge arrester in this way, if over-voltages do occur (potentially as a result of lightning strikes), then these are limited by the surge arrester to a magnitude of voltage which complies with the available electrical clearance values between the overhead line and structure.
Depending on the required protection level, surge arresters can be applied to the overhead line equipment on both sides of the structure – for each contact system running through the structure requiring a reduced electrical clearance.
Surge arresters have now been specified by Network Rail for a structure in Cardiff, where restrictions caused by the proximity of a canal, combined with a rail intersection bridge, mean that the track simply can’t be raised or lowered to accommodate compliant electrification clearances.
The Sicat system has already been installed on nine routes across the Danish railway network, covering a total of 1,300 kilometres of new electrified line.
Danny Aisthorpe is engineering director, rail electrification with Siemens Mobility.
This article first appeared in Issue 177 of Rail Engineer, Aug/Sep 2019.