Overhead conductor selection based on transient current and temperature analysis for better traction electrification system economics

Power demand of traction power supply systems is rapidly fluctuating as trains accelerate and decelerate, as route gradients change, and as the trains enter and leave power distribution sections. This fluctuating load needs to be delivered to the trains by overhead distribution system conductors and, therefore, the conductors need to be adequately sized for the envisaged current profile to prevent conductor overheating, annealing, and damage. Two methods of evaluating conductor current-temperature relationship are available, steady-state and transient. The steady-state approach of determining the conductor steady-state currents, and then selecting conductor sizes based on their ampacities, is suitable for relatively slowly-varying loads. However, the method could result in oversizing of conductors and an uneconomical system design when dealing with rapidly fluctuating loads. The transient method is more appropriate for fluctuating loads. First, transient current profiles of conductors based on traction power load-flow simulations of future train operation are determined versus time. Subsequently, temperature profiles corresponding to the current variations are developed for proposed combination of conductors. Only the conductors operating at below the temperature limit advised by the conductor manufacturer should be selected. A procedure for evaluating transient conductor temperatures taking into account current fluctuations is developed and demonstrated on several typical examples. Based on the evaluations, suggestions for selection of appropriate conductor sizes that would result in more economic electrification system designs are provided.