Influence of Steel Oxidation on the Behavior of the Wheel–Rail Electrical Contact in Dynamic Conditions

The safe management of traffic on rail networks requires that trains can be reliably located at all times. In many countries, this is achieved by electrically identifying their presence using ‘track circuits’ at regular intervals along each track: these devices detect when the wheels and axles of a train short-circuit the two rails (they are said to ‘shunt’ them) and the information is passed on to the signaling system. The quality of the electrical contacts between the rails and the wheels obviously plays a decisive role in the correct operation of this detection principle. The occurrence of high wheel–rail contact resistances can lead to malfunctions, known as ‘deshunting’, in which the system is unable for a certain period of time to conclude whether a train is present or absent on a section of track. This type of potentially risky event must obviously be avoided at all costs. In this article, we present the second part of a study devoted to the degradation of the wheel–rail contact resulting from steel oxidation, using a scaled-down home-made test bench that reproduces the real contact in the laboratory under controlled conditions. Following on from the first part, which dealt with the static characterization of the contact studied in the direct current, we are now tackling its dynamic characterization (rolling contact) under AC electrical conditions close to those of a track circuit. These new investigations again involve different degrees of rail oxidation, and analyze the influence of parameters such as contact force, speed, and current intensity.