Statistical process control model for switch failure detection and maintenance effectiveness assessment

Railway switches are crucial not only for normal operation of the railroad system as they guide trains to a track or platform, but also when disruptions occur since they allow trains to take alternative routes. Switch components and functions require frequent inspection, maintenance and renewal, making of switches a costly asset. The switch moving parts are subject to high deterioration and prone to malfunctioning, posing a safety hazard if no immediate action is taken. Nowadays online condition monitoring, standardization of inspection and maintenance actions, as well as data-based models are some of the tools supporting decision making for preventive planning, cost reduction and process effectiveness. This contribution presents a data-based model (derived from features extracted from measured point engine current during switch blade movement) for switch status nowcast and forecast applying statistical process control (SPC) methods. The SPC model is capable of identifying abnormal switch behavior; through examples it will be demonstrated how emerging failures in an early stage of development can be detected without the need of a labelled training data set of historical failures. The SPC model offers advantages over commonly used monitoring systems, as it does not rely on manually set switch-specific thresholds and references to detect the switch blades movements used to trigger alarms in these systems. Switch maintenance takes place regularly, sometimes significantly affecting the switch functional normal behaviour. Thus maintenance restricts somewhat the applicability of the SPC model. This contribution includes the discussion of methods applied for integrating the maintenance actions into the model. In turn, the SPC model output is used to assess the effectiveness of maintenance and the completeness of the reported actions performed on the switch. This work is partly funded by the EU H2020 and Shift2Rail Joint Undertaking projects In2Rail and In2Smart. The measurement data of the railway switches is provided by Strukton Rail