Vacuum Arc Evolution Characteristics in Low-Voltage DC Current Interruption Under Composite Transverse Magnetic Fields

Based on our novel dc vacuum interruption technology under composite transverse magnetic fields (TMFs), the arc voltage of dc vacuum arc can be effectively improved to interrupt the dc current. The objective of this work is to experimentally investigate the vacuum arc characteristics and their evolution in dc current interruption under composite TMFs. The composite TMFs were generated by both multipole permanent magnets and cup-type TMF contacts. The vacuum arc photos were recorded by a high-speed camera. The experimental results indicate that under these composite TMFs, the dc current could be successfully interrupted, which was closely related to the dc vacuum arc characteristics and their evolution. The experimental dc current and voltage were less than 500 A and 500 V. First, the evolution of the dc vacuum arc could be divided into Stable and Unstable stages, according to the characteristics of the arc voltage waveform. In the Stable stage, the dc vacuum arc might be stagnated, constricted, and rotated with a stable arc voltage of 20 V. In the Unstable stage, the dc vacuum arc was transferred to the outer periphery of the contact in the form of a “C”-shape, and the arc voltage significantly increased higher than the supply dc voltage. Second, there was an Extinction Area in the middle of Area 4 under the composite TMFs, which made the dc vacuum arc always extinguish at this position. Third, repeated fluctuations of the arc voltage are caused by the formation and extinction of the “C”-shaped arc. Finally, when the distance between the igniting area and Extinction Area increased, the duration of the Stable stage increased, while the duration of the Unstable stage decreased.