A complete circuit breaker model for calculating very fast transient voltages

Various studies have been carried out to determine the origin, the development and the effects of very fast transients (VFT) in GIS-Busbars. To date little knowledge exists on how VFT propagate through a high voltage circuit breaker, when the interrupter itself is the source of the VFT. For the development of circuit breakers it is important to know if these VFT are able to affect the dielectric coordination of the interrupter. In order to determine transient voltages at different locations inside an interrupter unit a numerical model has been derived. The model approach represents the circuit breaker as a system of concatenated transmission lines. The simulations were compared to measurements of a real circuit breaker and prooved the accuracy of the model in the frequency range from 9 kHz up to 500 MHz. This model allows future parameter studies which show the dependence of VFT overvoltages on the geometry of the circuit breaker.