DC interruption principle using a helical arc arrangement

摘要

Electrical discharges have been used extensively in devices for interruption of fault currents. Much work has investigated the use of arc discharges for interrupting DC current. The problem with DC current is that there is no natural current zero where thermal losses from the arc dominate thus leading to arc extinction and the interruption of fault current. Helical arc been arranged by using splitter blades to separate the arc turns. The expansion of a helical arc confined between polymeric splitter blades is governed by both electromagnetic and aerodynamic forces. These arise due to the complex interaction between the individual arc turns, arc/ splitter blade interactions and surrounding media. These interactions can be exploited to control the rate of expansion. During this expansion stage there is a substantial increase in arc voltage which in low voltage systems can limit the current thereby causing current interruption providing the arc quenching conditions are suitable. An experimental study has been undertaken to assess the fundamental characteristics of helical arcs con�fined between �different arrangements of PTFE, PE and copper blades in three different sizes (180mm, 360mm and 500mm). Significant improvements in arc current limitation and interruption capability are observed when the arc voltage increases. A substantial increase in arc voltage was observed for all combinations of copper/ PTFE splitter blades. It was noted that the prospective fault current is forced to near zero when copper blades are used in conjunction with PTFE blades. With the larger PTFE and PE blades sized 360mm and 500mm, it was observed that the arc stayed within the limit of blades, thus providing better arc control capability. Simplified modelling of the forces acting on the arc (electromagnetic, aerodynamic) have been assessed. The electromagnetic forces act not only to produce radial expansion of the arc but also to keep alignment between the turns. The generation of the aerodynamic forces is very complex to model and indeed the modelling presented can only be used indicatively in any analysis at this stage. The work indicates that a compact DC interruption device may be possible based on the confinement of the plasma within the splitter blades and interaction with polymeric material.