Development of 3-D Electromagnetic Thermal Fluid Simulation for Analyzing Movement and Disappearance of Multiple Cathode Spots in Vacuum ARC

Recently, it is required to elucidate the movement factor of multiple cathode spots in vacuum arc, which can improve the performance of the VCB (Vacuum Circuit Breaker), surface treatment of metal and physical vapor deposition. Multiple cathode spots in vacuum arc move at high speed with evaporation from cathode and interact with each other, which causes the disappearance and generation of the cathode spots unpredictable. Since the movement and interactions of multiple cathode spots in vacuum arc is complex physical phenomenon, the movement factor of multiple cathode spots has not been clarified. Therefore, it has been expected to elucidate this phenomenon by using numerical simulations. Some researchers have researched vacuum arc using 2-D symmetric MHD simulations. However, it cannot simulate the movement and disappearance of multiple cathode spots because the vacuum arc with multiple cathode spots is the asymmetric physical phenomenon. In this research, 3-D electromagnetic thermal fluid simulation was developed in order to elucidate the movement and disappearance of multiple cathode spots in vacuum arc. In this simulation, the current density distribution of cathode spots was determined by the ionic conductivity for the analysis of movement of cathode spots. The initial placement of cathode spots was fixed, the distance among cathode spots was set in the case of narrow distance and wide distance for analysis of constricted arc and diffused arc. As a result, some cathode spots disappeared and caused the of current density increment of the remain cathode spot, which leads to the increment of temperature over one cathode spot. This is because the increment of the conductivity above one cathode spot with increasing vapor concentration from cathode and the number density of electron. This is caused by the joule heating with increasing the current density of one cathode spot. Therefore, the movement and disappearance of multiple cathode spots in vacuum arc can be analyzed by this 3-D electromagnetic thermal fluid simulation.