An Approach to Model Very Fast Transients in High Voltage Circuit Breakers

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 few knowledge exists on how VFT propagate through a circuit breaker, when the interrupter itself is the source of the VFT. Further it is important to know if these VFT are able to affect the dielectric coordination of the interrupter. A numerical model approach is introduced which allows to investigate the VFT devolution within the circuit breaker. The model approach consists of representing the circuit breaker as a system of concatenated transmission lines. The model validation is done by measuring the S-Parameters (frequency domain) and the step response (time domain) between different ports of the modeled item. Consequent application of the modeling principle led to a model which represents the electrical properties of the circuit breaker accurately up to a frequency of 1 GHz. The use of this model will help to understand the effects of VFT on the dielectric coordination of the circuit breaker and its dependencies of further elements e.g. grading capacitors or network elements.