Measurements and simulations of switching events on a three phase three winding transformer

Power transformers are important electrical and sensitive equipment in the energy transmission and distribution system. Three phase three winding transformers are used to connect different high voltage levels and the third winding fulfils the task, to control the voltage level and for current compensation. Capacitor banks or shunt reactors can be connected on the tertiary part to increase or decrease the voltage level in case of network operations. Circuit breakers are used to connect and disconnect these elements and cause switching transients. To evaluate the transient stress on the tertiary part of the transformer, field measurements and numerical simulation with EMTP-RV were performed. A good correlation between the measured line-to-ground voltage and the numerical simulation results could be shown. Based on the numerical simulation model, the transient voltages could be investigated in more detail and also the effect of optimization requirements, to reduce the transient stress, could be investigated.