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Thermal evaluation of railway transformer used in autotransformer feeding systems

Globally, railway electrification is increasing at a fast rate and the overall power demand is expected to increase in the future to accommodate an increase in traffic volume and higher train speeds. However, due to dynamic train operation characteristics, the load profile at the feeder substation fluctuates and can reach beyond the transformer rating during peak timetable periods. This paper presents a multi-train simulation platform for an autotransformer feeding system using multi-conductor approach. Temperature is a key factor in the operational lifetime of a transformer, influencing the rate of insulation ageing processes. Sudden load variations seen in railway systems can pose a threat to the traction transformer's lifetime. Hence, a thermal model is integrated into the simulation, with parameters considered appropriate for the transformer, in order to assess the temperature of the hottest spot within the transformer. This model links temperature to load, and, given the propensity to push more trains through old assets as electrification of transport becomes en vogue, this relationship becomes ever more important. Consideration is given to the anticipated effect of the temperature profile on a traction transformer at a substation by making use of IEC standards for power transformers with appropriate modifications to traction transformers sourced from literature. It is found through the use of this model that traction transformers are not at high risk of thermal failure, however, some mitigation may be required against dynamic behaviour that can lead to conditions conducive to dangerous flashover events.