48 / 2018-08-20 10:55:44

Experimental Study on Arcing Process of Vacuum Arc under Wan-Type Contacts

vacuum arc,transverse magnetic field,arc appearance,arc voltage

With the outstanding advantages of large interrupting capacity, high reliability, small size, especially little environmental pollution, the vacuum switch has been widely used in medium voltage power distribution systems. As the core component of the vacuum switch, the structure of the contacts determined the vacuum arc characteristics, and then impacted the contact erosion greatly and played a decisive role on the interruption performance of vacuum switch.

In this paper, combining the actual demand for the development of the vacuum switch nowadays and the task of the National Natural Science Foundation of China (Grant No. 51777153), a series of numerical simulations and experimental researches were carried out on the wan-type transverse magnetic field (TMF) contacts. Firstly, the 3D finite element models of wan-type TMF contacts were built, the magnetic field distribution between the contacts and the electromagnetic force of the arc column were calculated. Then the experimental system for researching the characteristics of TMF vacuum arc was established. In the experimental system, the experimental contacts were installed in a demountable vacuum chamber and a sinusoidal current was supplied by an LC oscillation circuits. A high-speed charge-coupled device video camera with an exposure time of 2 us and a framing rate of 17000-19000 was used to record the arc appearance, the current and arc voltage waveforms were measured by a Rogowski coil and a high voltage probe respectively.

Based on the experimental data, the arcing process under TMF was investigated and was divided into three stages: the arc ignition stage, arc voltage rising stage and arc voltage declining stage. Combining with the results of simulation analysis, the influence of breaking currents on magnetic field distribution and electromagnetic force were analyzed, and the characteristics of arc appearance, variation of arc voltage and the duration of voltage noise during different stages were analyzed respectively. The results of simulation analysis revealed that as the peak breaking current gradually increased, the magnitude of transverse magnetic field between the contacts increased, and the electromagnetic force increased quadratically. Corresponding experimental results, it was found that as the experimental peak breaking current increased from 4.72kA to 13.2kA, the expansion speed of vacuum arc had an obvious increase and the arc appearance was more constrictive, the duration of the arc ignition stage decreased from 1.75ms to 0.75ms, and the first peak of arc voltage increased from 38V to 80V. In addition, when the peak breaking current reached up to 6.08kA, the voltage noise was more obvious and as the breaking current increased continuously, the voltage noise gradually occurred earlier and ended later, making for an increasing duration. Meanwhile, the voltage noise was always accompanied by short-time constriction of arc or bright cores in the arc column. When the peak breaking current was more than 13kA, a special phenomenon with the arc root moving along the edge side of anode was observed, leading to a melting speed of about 65m/s, which was equivalent to the velocity of arc movement. This phenomenon would cause serious erosion to the contacts and usually indicate that the contacts have reached to the breaking limit. The research results of this paper could provide reference for the structure optimization of the wan-type TMF contacts.