Effects of nozzle and contact geometry on arc voltage in gas circuit-breakers

At the high voltage laboratory at ETH Zurich switching arcs are investigated in order to understand the physical processes that determine the relationship between current and arc voltage in gas blast circuit breakers. Experiments are performed using a breaker prototype with many independently controllable parameters, and very versatile pulsed DC current source. Previous work showed that the gas pressure has a strong influence on the arc voltage, therefore changing the fluid dynamic conditions in which the arc burns can be used to create different dU/dI characteristics. In the presented paper a method to quantify these changes is presented, and the impact of the axial position of the contacts in a model gas circuit breaker on the voltage as function of current are discussed. The influence of the contact position on the average dU/dI curve were small, but the fluctuations around this average value change depending on the nozzle section in which the arc burns. These results will be used to improve the theoretical understanding of the different arc cooling mechanisms, which in turn should enable the design of new geometries that result in a more favorable arc voltage characteristics for passive oscillation HVDC circuit breaker topologies in the future.