Investigations on contact erosion in vacuum circuit breakers by arc rotation measurements with external magnetic field sensors

This research project focuses on developing a measurement system which is able to detect the arc motion in a RMF (radial magnetic field) contact system. The arc movement is measured by analyzing the magnetic field signals of several external induction coils detecting the magnetic field changes from the rotating arc. In this way it is possible to analyze the dynamic characteristics of constricted vacuum arcs rotating in a commercial vacuum circuit breaker. The main benefit of this approach is that commercial vacuum interrupters can be tested. The working principle of this measurement system is discussed, as well as the additional effects that need to be taken into account to correctly analyze and interpret the measured signals. The contact erosion can cause two or more spiral arms melt together, thereby eliminating the RMF and decreasing the performance of the contact system. In this new approach, measurements of the rotation behavior of a constricted arc made it possible to detect when this event happened. The rotation behavior of constricted arcs was measured during the entire lifetime of a circuit breaker to observe the erosion phenomena step by step. With this method, the performance limit of the circuit breaker can be detected before the end of life is reached.