50 / 2018-08-20 11:15:07

Influence of Contacts Diameter on the Vacuum Arc Characteristics of Spiral-type Contacts

vacuum circuit breakers,arc characteristics,TMF contacts,contacts diameter

With the development of the contact materials, the improvement of manufacture, and the introduction of arc control system, vacuum circuit breakers gradually developed towards larger interrupting capacity, higher reliability and less environmental pollution. Based on the current development of transverse magnetic field (TMF) contacts, this paper completed the experimental research and numerical simulation to study the influence of contacts diameter on vacuum arc characteristics between spiral-type contacts by considering the axial magnetic field (AMF) and the electromagnetic force. Moreover, this paper could provide reference for the design of vacuum interrupters with TMF contacts and the research of vacuum arc.

In this paper, the 3-D finite element simulation models of spiral-type contacts with different diameters were established. The ratio between the maximum value of AMF and TMF on the cathode contact surface at 8kA peak breaking current was calculated. The simulation results showed that, with the increase of the contacts diameter, the ratio became larger. The 30mm diameter contacts had the ratio of 0.312, and the 48mm diameter contacts had the ratio of 0.646. The axial magnetic field could drive the vacuum arc to transform to the diffuse mode earlier, and avoid severe ablation on the contact surface. Increasing the breaking current, arc column would begin to rotate on the contact surface under the function of transverse magnetic field. At 20kA peak breaking current, when setting the arc column on the center of the contact and enlarging the contacts diameter, the electromagnetic force increased from 46.8N to 55.6N. Then the arc column was set on the front section and the rear section of the contact arm, the force was 63.6N-68.9N and 70.3N-78.9N respectively. It indicated that increasing contacts diameter could help to enhance the control ability of arc motion and prolong the working life of contacts.

Combined with the simulation results, experimental research was set up by using two set of spiral-type contacts with different diameters (30mm and 48mm), the arc appearance characteristics and the arc voltage changes were analyzed during the three stages of arc process including the initial ignition stage, the arc voltage rising stage and the arc voltage declining stage. It could be seen from the experiment that the arc characteristics of the two set of contacts were not much different during the first stage, the arc voltage after ignition was 30V, and the duration of this stage was both 1.8ms. In the second stage, the contacts with 48mm diameter had larger axial magnetic induction, which had more stable arc motion correspondingly, and the duration of the arc voltage rising stage was 4.225ms. Oppositely, there were more obvious arc movements on the anode of 30mm diameter contacts. The duration of this stage increased to 5.185ms, and the arc voltage waveform was accompanied by more noise spikes. During the third stage, the arc activities intensity between two set of contacts both decreased, but the arc movements in the contact gap of the 30mm diameter contacts were more severe than that of 48mm diameter contacts. Then the arc energy of two set of contacts at different peak breaking currents were calculated. With the increase of the peak breaking current, the current density and arc voltage also increased, and the arc energy showed a growing trend. Furthermore, we could observe that at the same breaking current, the 30mm diameter contacts tended to have higher arc energy, and it reflected that larger diameter increased the arcing energy sharing space efficiently, which could avoid partial serious erosion, and enlarge the interrupting capacity.