Switching transients in a 2 × 15 kV 16.7 Hz autotransformer railway system

This study presents the analysis of transient states generated along the traction catenary during switching operation in the main supply substation unit. For this purpose, a Swedish autotransformer railway system operating at 15 kV and 16.7 Hz has been chosen as a reference. The simulations of abovementioned system were conducted using EMTP-ATP software. This study presents results of simulations for various conditions and at different loads. The main outcome of the analysis is determination of transient currents and voltages in the system during catenary energisation and de-energisation process. Due to the presence of saturable autotransformers along the catenary the flow of excessive inrush current may lead not only to the overloading and as a consequence main breaker tripping but may also cause slow-front overvoltages. In order to represent the worst case conditions parametric study was performed. It includes variable tripping time of the main circuit breaker and pre-existing residual core flux. The results of the analysis show that the system response is strongly dependent on the breaker closing and opening times. As a consequence, it is possible to determine safe switching conditions in order to avoid large overvoltages or accidental tripping.