Operational fault states in railways
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In railway systems, there are many different fault states which can occur during operation. For safety reasons, these well known fault states have to be prevented by train monitoring. But fault states may also have dependencies among each other, which are not sufficiently known yet or used for fault state prevention.
Approach of systematic description
Thus, in a first step an abstract approach has been developed for the description of dependencies. Based on this and as systematic description of all relevant states and their dependencies a fault state matrix has been created, which is considered in this paper.
KeywordsFault states Railway operation Safety Cause-consequence-dependency
If there are no measures for recognition, the final consequence of many fault states is a derailment. Therefore it is necessary to prevent the long-lasting occurrence of all critical fault states. Because of the movement of the train, most of the relevant fault states can not be observed directly. Thus, suitable indicators have to be measured, which can be done by onboard or wayside monitoring systems .
2 Fault state matrix
2.1 Fault states
Derailment: at least one wheel is not running on the rail
Hot Box: axle-bearing exceed temperature threshold
Blocked Brake or Wheel: permanent braking of a wheel or an axle (rotating wheels and axles as well as blocking ones)
Faulty Flash Guard: missing flash guards or flash guards which are not able to prevent sparks touching vehicle
Faulty Elements of Brake System: faulty elements of the braking system (brake valve, brake leverage, etc.), which cause continuous braking
Breakage of Stub Shaft
Faulty Running Surface/Wheel Spot: failure on the running surface (flat spot, pitting, rewelding, polygonal, etc.)
Faulty Flange of Wheel: too high wear (exceeding operational threshold) or flange with broken out parts
Faulty Suspension and –component: faulty suspension spring (wrong or different types installed, loosen or displaced spring band, cracks), broken suspension springs, broken or missing parts of suspension (suspension ring, elements of shock absorber), faulty suspension bracket (cracks, broken)
Faulty Frame: cracks and breakages on structural parts (mainly in the section of integration of crossbar in main frame), buckling of chassis, longitudinal buckling respectively forbidden deflection
Unbalance (during vehicle’s run): different wheel load (left-right and/or front-rear) - only one single train journey considered in this context
Displacement of the Load
Overload (continuous): wheel, axle or car load exceeding operational threshold. In this context this fault state occurs during several train runs.
Violation of Clearance Gauge
Faulty Car Opening (Doors, Loading Trap, etc.): faulty car openings like doors, loading traps, sliding-walls, etc. which are not reliable closed or which are opening during the run
Faulty Load Fixation and Fastener: faulty belts, tarps, fixation net, stanchion
Insufficient Lubrication of Buffers
Faulty Buffer: dragged-in buffer disc, faulty spring element, loose or missing fixation elements, too high end play, cracked weldseam
Overriding of Buffers
Faulty Electrical Car Equipment: faulty electrical devices/systems e.g. air conditioner, heating, ventilation, light
Broken Pantograph: breakage of sliding contact
Fire on/in board
Objects within the Clearance Gauge: objects, which are lying on the superstructure and entering the clearance gauge
Variation of Width of the Track Gauge: exceeding or narrowing of the track gauge over allowed thresholds
Track Distortion: parallel, horizontal and/or vertical displacement of both rails and of sleepers
Faulty Rail Surface head checks, short-pitch corrugation, plastic yielding, etc.
Faults inside Rail: inclusions of material and welding failures
Worn Rail: lateral wear, longitudinal wear, etc.
Aged Rail Material: changed characteristics of rail material caused by fatigue or ageing
Broken Rail: all types of breakage (brittle fracture, comminuted fracture, etc.)
Faulty Elastic Rail Pad: faulty or missing elastic rail pad
Faulty Rail Fastening/Ironmongery: slack or broken rail fastening (bolts, clamps, etc.)
Aged Timber Sleeper
Cracks in Concrete Sleeper: longitudinal or lateral cracks
Insufficient Track Bed: wear of ballast, too less edge of ballast, reduction of bearing capacity due to insufficient drainage, base failure of an embankment, elevation due to poor frost resistance, etc.
Description: Wear of ballast causes subsidence. This might cause failures of the track. Therefore the proportion of Y and Q forces might be higher and a derailment might be the consequence. Moreover a reduced edge of ballast might reduce the lateral resistance and a track distortion might be the result.
For the reasons of the analysis and the validation of the supposed logical connections between different safety related fault events and states in the railways, a network of technical train monitoring components must exist. The data acquisition can be done on the vehicle-side or wayside or both together. Based upon research projects within the last years several sensor systems are now available which can be used for automated monitoring. Aim of such devices is to increase operational quality by means of prevention and therefore to guarantee a safe and reliable transport of passengers and goods. The key issue by the observations is the evaluation of the proper correlation of the collected data (allocation of fault state to vehicle number). If this practical problem can be solved, a huge database of monitored parameters and therefore of particular detailed information about important fault states and events will be available.
Under consideration of dependencies between failure states reactions on recognized failures states can be optimized. This causes a reduction of loss by prevention of secondary losses and improves the safety of railway operation. Based upon reduced secondary losses the availability of rolling stock and infrastructure should increase and therefore the efficiency of operation should also increase. Therefore a cross border recording along the European corridors is required.
Annex III of directive 2008/57/EC  specifies the essential requirements on interoperability which a railway system has to fulfill. Safety is one of these essential requirements and is defined by several requirements. One of them is for the design, construction or assembly, maintenance and monitoring of safety-critical components, and more particularly of the components involved in train movements.
In accordance to directive 2008/57/EC the railway companies must verify this at least in context to the conferral and monitoring of safety authorization based upon article 11 of directive 2004/49/EC  and for licensing and supervision of safety certification based upon article 10 of directive 2004/49/EC.
In the recently started European project “D-Rail - Development of the Future Rail Freight System to Reduce the Occurrences and Impact of Derailment” this methodology will be applied to identify failures in railway operation, which have to be monitored to prevent derailments.
Described work was funded by the Austrian ministry of transport, technology and innovation in the frame of the program ISB – “Innovative System Railway”.
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