Verhalten unterschiedlicher Kontaktsysteme in Vakuumleistungsschaltern bei hohen Schaltleistungen

Behavior of Different Contact Systems of Vacuum Circuit Breakers under High Switching Capacity ABSTRACT The aim of circuit breakers is to interrupt high short-currents and to separate the faulty equipment from the grid. In medium-voltage systems the vacuum circuit breaker dominates with still increasing market share. There is a strong interest to reduce the costs and the of interruption chambers, but keeping their breaking capacity. The basic knowledge of the dominant phenomena is essential for further improvement. This dissertation deals with the breaking behavior of vacuum interrupters under high current stress of 10 to 60 kA. The transient recovery voltage (TRV) level during most measurements amount to 36 kV. Additionally, experiments were carried out with TRV peaks up to 120 kV and with varying TRV steepness du/dt. Switching tests were carried out in a single-phase synthetic test circuit. In vacuum circuit breakers two different contact types are used to overcome the consequences of arc constriction. Radial magnetic fields (RMF) force the constricted arc to rotate and distribute its power more evenly on the contact surface. Axial magnetic field (AMF) contacts prevent the arc from becoming constricted up to higher thresholds. Arc and current-zero behavior of different AMF-contact designs are discussed. Video sequences with a high-speed camera (20 000 frames/s) were taken to analyze the arc behavior of the different AMF-contact types and of radial magnetic field (RMF) spiral contacts as well. To analyze the period around current zero, post-arc current was measured. This is a direct indication of the residual charge in the gap at current zero. The residual ionization has a direct influence on the re-ignition tendency. The dissertation shows the correlation between AMF, which due to eddy currents still exists when the current approaches zero, and the post-arc behavior.