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

Abstract

Abstract-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.

Influence of Ablation on Differential Arc Resistance

“…According to the considerations described in [5] and [7], the voltage and current data of the high current phase was evaluated using the median value instead of the mean, to be more robust against fluctuations. The error bars in figures 3 and 4 are indicating the 15.9 and 84.1 percentiles.…”

“…The nozzle geometry is shown in fig. 1, and identical to the one presented in [5]. The inlet directly attaches to the inlet pressure volume and has a diameter of 50 mm.…”

“…The setup used was previously described in [3], [5], [6]. It consists of a model gas circuit breaker, which uses gas bottles for a freely adjustable blow pressure and two contact pins of which one is movable to draw the arc.…”

Determination of Axial Electric Field Distribution in Blown Arcs With Differential Method

“…The downstream contact is mounted to a pneumatic actuator for movement. This is used to initiate the arc, as already described in [4], [12], [13]. During this opening process, a small "pre-current" of 50 A to 200 A is applied, and the valves for the blowing are triggered to open.…”

“…To determine the u(i) relationship, the more robust median is used, and the arbitrarily chosen 5-and 95-percentiles are used to quantify the fluctuations. This is motivated by [11] and described in more detail in [12].…”