Combating the cold weather

With a national rail network extending from Penzance in the south to Thurso in the north, the vast majority of the UK’s railway infrastructure rests in a moderately agreeable band between 50.12° and 58.59°. Even in this comparably comfortable region, however, we are still at the mercy of the seasons. Spring rains threaten embankments and floods in one part of the country can have countless knock-on effects elsewhere. In the summer, our comparably moderate maximum temperatures still bring the risk of buckled rails. In the autumn we must contend with issues of high winds, adhesion, and the infamous ‘leaves on the line’. And in the winter we are plagued by both operational and maintenance disruptions caused by ice and snow. Since 2006, the Birmingham Centre for Railway Research and Education (BCRRE) has been undertaking work to understand and mitigate the effects of ice and snow on the UK’s railway network. While some of this has involved taking measurements from the live railway, the group has steadily been developing a suite of facilities and standard tests which can be used to evaluate the winter resilience of a number of components of the railway infrastructure.

Third rail

The vast majority of the UK’s third rail network is located south of London where it makes up a significant portion of the lines. The network itself is configured as a top running conductor rail electrified at a nominal 750 V DC. This means that the contact point between the train’s collector shoe and the third rail is on the rail’s top surface. This configuration can have significant disadvantages in winter conditions as ice can form on the surface of the rail and then act as an insulating layer between the supply rail and the train. For this reason, top running third rail systems in parts of the world with climates any worse than the UK are often shrouded against snow or ice formation.

In the UK, a number of different approaches to the ice formation problem have been considered with tests undertaken at the University of Birmingham to evaluate some of the candidate solutions. The first work under – taken was to consider the possibility of increasing the contact force between the conductor shoe and the rail. The tests made use of BCRRE’s spinning rail facility shown in Figure 1. The nominal contact force was varied through static loading to identify any effects on the ability of the conductor shoes to clear the formed ice. The tests showed that the loading had limited effect when compared to the condition of the conductor shoe itself.

In 2008, further testing was undertaken. This time the tests considered a number of different shoe designs and looked at the dynamics of the interaction between the conductor shoe and the third rail. Example shoes and outputs are shown in Figure 2. Custom ice clearing shoes were moderately effective, but those suitable for current collection worked less well for ice clearance. While the different shoe designs had limited effects or exhibited prohibitive wear profiles, the instru mentation indicated a correlation between pitching of the conductor shoe and ice clearance. This was attributed to the toe of the shoe digging into the ice and causing sections of it to be removed through fracturing. This pitching behaviour, along with other shoe dynamics, was later verified in a series of field experiments.

By 2010, the proposed methods for ice clearance had largely moved from physical to chemical. BCRRE developed a standard suite of tests to be used in the evaluation of commercial de-icing products offered to Network Rail for use on the third rail network. The tests used the spinning rail facility to not only evaluate the ice clearing capacity of the products but also their resilience to both mechanical wear by conductor shoes (see Figure 3, page 31) and to further precipitation. Testing in the 2010 season also included evaluation of sleet brushes for ice clearance. This highlighted appreciable performance but also demonstrated an issue relating to the alignment of the tines in which a furrow effect still prevented rail/shoe contact being made (see Figure 4, page 32). BCRRE staff modified the test sleet brush with a new alignment and repeated the test showing a dramatic improvement in performance.

In 2011, Network Rail was searching not only for reactive de-icers, but for preventative antiicier products to apply to the third rail. The standard suite of de-icer tests was expanded to allow evaluation of anti-icing properties and a new round of testing was undertaken. In addition to conventionally applied (sprayable) chemical products, Teflon and Silicone based rail coatings were also evaluated. These form a coating over the rail on which moisture pools such that when it freezes it forms ‘baubles’ with low surface contact and adhesion. The removal of these baubles was shown to be largely dependent on the sharpness of the edge of the removing conductor shoe.

More recently, in 2012, BCRRE have worked with RVEL to test configurations and deployment mechanisms for equipment to be mounted to Snow and Ice Treatment Trains (SITT). While initially involving alternative mountings for castellated conductor shoes and sleet brushes, these tests also involved adapting the test facilities to support hot-lay chemical de-icers. The testing itself consisted of variations in component type and sequence along the train as well as fluid deployment sequence and rate.

Ballast

While the formation of ice on the third rail presents an operational issue, ice in the ballast can result in substantial disruption to maintenance schedules. Holiday periods, such as those around Christmas, are often used to schedule track renewal works such that disruption to commuter traffic is minimised. Unfortunately these periods are among those most likely to be affected by freezing conditions. Ballast is used in track to provide support while allowing drainage. Should the ambient temperature fall, however, any moisture remaining in the ballast can freeze in the inter-particle spaces bonding the ballast particles togetherallow evaluation of anti-icing properties and a new round of testing was undertaken. In addition to conventionally applied (sprayable) chemical products, Teflon and Silicone based rail coatings were also evaluated. These form a coating over the rail on which moisture pools such that when it freezes it forms ‘baubles’ with low surface contact and adhesion. The removal of these baubles was shown to be largely dependent on the sharpness of the edge of the removing conductor shoe. More recently, in 2012, BCRRE have worked with RVEL to test configurations and deployment mechanisms for equipment to be mounted to Snow and Ice Treatment Trains (SITT). While initially involving alternative mountings for castellated conductor shoes and sleet brushes, these tests also involved adapting the test facilities to support hot-lay chemical de-icers. The testing itself consisted of variations in component type and sequence along the train as well as fluid deployment sequence and rate. Ballast While the formation of ice on the third rail presents an operational issue, ice in the ballast can result in substantial disruption to main – tenance schedules. Holiday periods, such as those around Christmas, are often used to schedule track renewal works such that disruption to commuter traffic is minimised. Unfortunately these periods are among those most likely to be affected by freezing conditions. Ballast is used in track to provide support while allowing drainage. Should the ambient temperature fall, however, any moisture remaining in the ballast can freeze in the inter-particle spaces bonding the ballast particles together. This bonded ballast is particularly difficult to remove from the track and can have a significant impact on the schedule of renewals processes.

In 2010, BCRRE undertook work for Network Rail to develop a series of tests to evaluate the effectiveness of a number of chemical de-icers when applied to sections of frozen ballast. The tests considered two situations – the bulk ballast itself and the release of panels of track embedded in frozen ballast. As with all other chemical testing, the tests were undertaken blind to cost and lead by Network Rail’s dosing levels; but in this case the quantities were also varied to identify those required for a successful application.

Following the testing, Network Rail achieved an improved capability for ballast removal during renewals. At this point a second issue relating to frozen ballast emerged. Once the ballast is removed it must be replaced with fresh ballast which is generally transported in auto-hoppers. As the ballast is stored outside, it can become damp and thus freeze into the auto-hoppers preventing deployment. In 2011, BCRRE produced a pair of structures simulating the form and mechanisms of an auto-hopper to identify appropriate levels of chemical de-icers to be applied in order for the units to remain functional.

Switch

The latest project undertaken by BCRRE in the area of winter preparation relates to ice formation in switches. This is a project funded by the TSB and RSSB under the ‘Accelerating Innovation in Rail’ call. BCRRE are working with a number of project partners including Heat Trace Ltd. to develop self-regulating heating systems for use on points. While the project partners are looking at material substitutions, cable designs, efficiency savings and safety improvements; BCRRE have developed a thermal model (see Figure 5) of the entire switch allowing rapid evaluation of candidate designs and applica – tions. Further to this, BCRRE have been undertaking full-scale physical testing of the most promising products and designs using a B-type switch contained in a freezer (see Figure 6, page 33). A number of evolutions of cable designs and application strategies have been tested along with multiple solutions for powering the cables in order to maximise compatibility with the railway environment.

Going forward

During the course of the aforementioned work, BCRRE has developed a substantial suite of facilities and standard tests for winter prepara – tion testing. This range is ever expanding with future projects likely to build on the testing already undertaken but also to link to other areas of work favoured by the group. In particular, the group has previously undertaken substantial research into condition monitoring of infrastructure assets such as points machines. It is likely that future projects may involve the extension of these condition monitoring techniques and algorithms to consider the performance of points machines in freezing conditions.

Acknowledgements

BCRRE would like to acknowledge their project partners and funders who have contributed to the work described in this article. In particular, Network Rail, ARUP and RVEL for the third rail work; Network Rail for the ballast projects; and the TSB, RSSB, Heat Trace Ltd. and other project partners for the switch project.

Biography

Dr Edd Stewart is a lecturer in digital logic and microprocessor systems at the University of Birmingham. His research work is delivered through the Birmingham Centre for Railway Research and Education where he leads on projects in the areas of condition monitoring, energy, winter preparation, and nondestructive testing. Edd is involved in research programmes in the UK, Europe, and also in the Far East where he is also involved in university relations and overseas teaching.

Clive Roberts is Professor of Railway Systems at the University of Birmingham and Director of Railway Research for the Birmingham Centre for Railway Research and Education. He works extensively with the railway industry and academia in Britain and overseas. Clive leads a broad portfolio of research aimed at improving the performance of railway systems, including a strategic partnership in the area of data integration with Network Rail and a European Regional Development Fund project to help SMEs develop products for the rail industry. Clive’s current research interests lie in the areas of: fault detection and diagnosis; system modelling and simulation; optimisation and data collection and decision support, applied to railway traction, traffic management systems, mechanical interactions and capacity. Clive heads a team of 12 Research Fellows and 24 PhD students. He is a Visiting Professor at Beijing Jiaotong University and in 2010 was named as one of the National Science Foundation of China’s International Young Scientists.