Study of Ablation of Arc Contacts and Dynamic Contact Resistance in High Current Breaker

Abstract

The fault of power circuit breaker (PCB) can lead very serious problems, especially in high voltage-power grid. The structure of contacts may be composed of main contacts and arc contacts, and this structure can avoid ablation of main contacts efficiently. It is necessary to study the eroded state of the arc contacts and the dynamic contact resistance of arc contacts to estimate the operating state of the PCB. The wear of contacts contains arc ablation and mechanical wear through the characteristics of contacts. The arc ablation is caused by the high temperature of the arc and the mechanical wear is caused by the mechanical friction of static and movable contacts. Some experiments have been done under different size of contacts and different current through them. The results show that the mechanical wear increases, sometimes heavier, with the increase of the size of fixed contacts and the decrease of the size of movable ones because the force between fixed and movable contacts becomes larger. The results also show that the ablation of arc contacts increases with the increase of current, especially when the current is up to 20 kA. With the high temperature of arc reaching the hardness point of copper, the arc ablation and mechanical erosion are increasing obviously since the contacts become soft and easy to wear. Another result of the study shows it is important to choose the material of contacts and the force between movable and fixed contacts. The harder and less resistance the material of contacts, the better the operating situation. To monitor the operating situation of the breaker, the dynamic contact resistance was measured 25 times. As a result, the dynamic contact resistance is sensitive to the current and increasing with the increase of continuous experiment time because of the increasing of metal ions. Furthermore, if the SF 6 in the PCB is changes, the dynamic contact resistance would be changed. The dynamic contact resistance in this experiment varies substantially within the range of 80-250 μΩ at the current of 20 kA.