Paul Zuijdervliet is Catenary Specialist at ProRail Infra Management. Serge Flore is Catenary Specialist and Frans Többen is a Consultant at Arcadis Infra BV
WHEN it opens in 2013, the Hanze Line will be available for trains to operate at up to 200 km/h. This will be the fastest speed permitted in the Netherlands under ProRail's conventional 1·5 kV DC catenary.
Now under construction between Lelystad and Zwolle (RG 12.06 p798), the 50 km Hanze Line was originally designed for 160 km/h at 1·5 kV DC with provision for conversion to 200 km/h at 25 kV AC. But the government's decision to abandon proposals for the long-discussed ZuiderZee Line focused more attention on ways to cut journey times from Amsterdam to Groningen and Leeuwarden. Conversion of the power supply to 25 kV has also been postponed, leading to the decision to investigate adapting the existing catenary for 200 km/h running.
ProRail commissioned Arcadis to examine the implications of faster running on the Hanze Line. Detailed modelling of the higher forces involved - particularly with respect to wear of the contact wire - led to modifications to the catenary design to optimise life-cycle costs.
Contact wire life
The reliability of any overhead catenary system depends very much on the life span of the contact wire, although of course this is not the only cause of costly failures or disruptive renewals. The contact wire is one of the most vulnerable overhead line components, and inevitably suffers wear from passing pantographs. Once the catenary has been installed, the wire life cannot easily be improved. The best that can be achieved is a carefully-planned maintenance regime, based on accurate assessment to pre-determine the amount of wear.
Professional asset management requires a good understanding of the various failure modes for the contact wire. This should lead to a design focused on effective maintenance policy. It is only through this approach that life-cycle costs embracing depreciation, maintenance and disruption recovery can be optimised.
The life span of a contact wire should be as long as possible, since replacement is costly, labour-intensive and requires taking the railway out of service. The huge increase in the price of copper during 2007 merely underlines the point.
A high degree of predictability leads to more accurate maintenance estimates and fewer inspections, and a crucial condition for such accurate predictability is a uniformly distributed wear pattern.
Any increase in train speed has an unfavourable aerodynamic effect on the dynamic behaviour of the catenary, and thus on the ability of the pantograph to maintain a constant upwards force on the contact wire. Not only will the wear rate increase; it will also become more irregular and reduce wire life even further.
Our study into faster running on the Hanze Line concluded that, with 200 km/h operation, the life span of the contact wire would be halved if no countermeasures were taken to reduce wear. Improvements to the catenary design were essential if the original life span was to be achieved.
Variations in contact force between the pantograph and contact wire are minimised when variations in the distance between the wire and the train roof are gradual and small in amplitude. Tolerances are defined for both track and catenary, and the study addressed the question of whether changing the tolerances would increase the variance in contact force (Fig 1).
It was found that at higher speeds the deterioration of dynamic behaviour caused by the proposed speed increase was greater than that caused by tolerance levels. It was therefore decided that altering the characteristics of the catenary system would be preferable to simply relying on tighter tolerances.
However, over a longer period of time the distance between contact wire and track can change, for example as a result of settlement in the track or supporting structures such as embankments. This is expected to be a significant issue for the Hanze Line, especially where the route crosses reclaimed land. ProRail has been advised to carry out regular checks and make corrections before contact wire wear gets out of control.
The case study showed that increasing the running speed with the normal pantograph configuration, but without compensating measures, results in an increase in the variation of the contact force of approximately 80%. Adapting the catenary design slightly would limit the increase to around 10%.
Based on the 160 km/h benchmark, it was determined that increasing the speed to 200 km/h could be expected to cause a 50% increase in failures of the catenary and pantograph systems sufficiently serious to disrupt train services. Altering the design to reduce the wear rates would decrease the probability of catenary failure.
Various changes were assessed on the rate of return on the expenditure involved and on the ratio of technical and cost effectiveness. Different combinations of catenary characteristics were examined, taking into account the complexities of overhead line - pantograph configurations and the increased traction currents needed for faster operation.
RAM(S) analysis was used to determine the technical effectiveness of the various alternative proposals. The availability of the overhead line is expressed in terms of a percentage relationship between the mean time between failures and total time MTBF + MTTR (mean time to repair). The RAM performance of the overhead line contributes to the overall availability of the railway as defined by Cenelec Standard EN50126.
The study concluded that if the standard catenary was used without modification, MTBF on the Hanze Line would be halved, doubling the cost of interruption recovery. And for each of these failures, MTTR would double due to longer function recovery times. The result would be a drop in the availability of the entire overhead line of 0·08%.
The proposed improvements offered approximately 35% less loss of reliability and also halved the MTTR, limiting the decrease in availability to 0·04% with respect to the benchmark. This is a gain of 50% on the do-nothing case.
Our study predicted that contact wire renewal costs would increase by more than 160% if no compensating measures were taken. Modifications to the catenary design would make it possible to keep maintenance costs at 200 km/h virtually unchanged, while the capital cost for the whole overhead line installation would rise by approximately 13%.
Despite the fact that this cost increase could be recovered through a longer life span of the contact wire, ProRail and the project management team for the Hanze Line project decided to modify the catenary design before installation. Criteria taken into account in reaching this decision were RAM performance, life-cycle costs and the impact of design modifications.
It was decided that the most favourable solution was to slightly shorten the distance between supporting structures, causing a rise of just 1% in the overall capital cost of the overhead line equipment. The life span of the contact wire was still considered acceptable. The slightly reduced level of improvement with a modified design was considered more cost effective than completely redesigning the whole catenary or making no changes at all. Moreover, the choice was considered 'robust' because of its other advantages.
Similar research has been conducted elsewhere. Examples include upgrading of the RE200 catenary system in Germany, and the step-by-step development of catenary for the high speed lines in France.
Final approval of the modified catenary system for 200 km/h operation on the Hanze Line will be based on dynamic measurements and monitoring. Procedures for commissioning and validation will ensure the successful integration of the modified catenary with other mechanical and electrical subsystems in the project.
- CAPTION: Typical ProRail 1·5 kV DC catenary is to be employed on the Hanze Line, but modification will be required for 200 km/h operation
- Fig 1. Adjusting the permitted tolerance in the distance between the train roof and catenary has less effect on contact forces at higher speeds
- Fig 2. The condition of the overhead line equipment will decrease rapidly without a good maintenance regime
- Fig 3. Based on ProRail's standard B4 design and typical train formations with five pantographs, uplift forces on the contact wire are significantly higher at 200 km/h than at 160 km/h