Simulation of vacuum arcs in circuit breakers based on kinetic modelling

The interruption of short circuit currents, reaching values of about 50 kA in medium voltage power systems can be seen as the greatest stress of circuit breakers. In order to come closer to their physical limits detailed knowledge on the behaviour of vacuum arcs is absolutely necessary. State of the art simulation tools are based on the assumption that a local thermodynamic equilibrium exists, but they do not consider certain instabilities, which are important for the switching process. With the aim to overcome some of these constraints a simulation tool based on kinetic modelling of the vacuum arc has been developed, which does not require any thermodynamic relations. To verify the theoretical description, experimental investigations on AMF-contacts have been performed. For this purpose a synthetic test circuit reproducing the real stress of a circuit breaker has been built up. By using a special breaker design, the vacuum arc is observed by a CCD camera.