Study on cathode spot expansion process in vacuum arc with high di/dt. (May 2023)

• Record Type: Journal Article
• Authors: Liu, Liming; Yuan, Zhao; Liu, Shan; Ye, Jingjing; Chen, Lixue
• Is Part Of: Vacuum. Volume 211(2023)
• Publication Date: 2023-05
• Subjects: Vacuum arc -- Cathode spot type -- T-F emission -- Arc voltage -- Unstable expansion; Vacuum -- Periodicals; 621.55
• DOI: 10.1016/j.vacuum.2023.111984
• Languages: English
• ISSNs: 0042-207X

Abstract

Abstract: The study on cathode spot under high d i /d t condition promotes the application of vacuum circuit breaker in DC transmission and aerospace technology. Cathode spot, as a source of microscopic particles, directly affects the breaking capacity of vacuum circuit breaker. In this paper, vacuum arc with high d i /d t was generated in L-C oscillating circuit. The cathode spot behavior was obtained by a high-speed camera. There are two types of cathode spots with different size, different expansion velocity and brightness. The difference in the size of different types of cathode spots leads to the difference in the thermal diffusion velocity of the spots, which is also the main reason for the difference in the expansion velocity of the two types of spots. The influence of spot current density on temperature and electric field is discussed. With the increase of d i /d t, the phenomenon of unstable expansion of cathode spots is observed. A new cathode spot is generated in the cold electrode area far away from the previous cathode spot area, resulting in a significant increase in the arc voltage. The expansion characteristics of cathode spot under different current amplitude, frequency and d i /d t conditions are obtained. Highlights: The physical mechanism and influence factors of cathode spot expansion under medium-high frequency current breaking were explored. Type Ⅰ cathode spot: large size, low expansion velocity and high brightness. Type Ⅱ cathode spot: small size, high expansion velocity and low brightness. The time constant of heating process for Type Ⅱ cathode spot is less than that of Type Ⅰ cathode spot, which leads to the faster thermal diffusion velocity. Thus, the expansion velocity of Type Ⅱ cathode spot is higher than that of Type Ⅰ cathode spot. The instability expansion of cathode spot occurs under the condition of high di/dt, which is related to the expansion process of cathode spot.