高压直流转换开关电流转换特性及其影响因素

High-voltage direct current (HVDC) transfer switches are key equipment in HVDC transmission system. We investigated the current commutation characteristics and its influential factors, and established a field-circuit coupled arc model of a 500 kV self-excited oscillatory HVDC transfer switch by deducing and discrediting the fundamental circuit equations satisfied by transfer switches. Firstly, the current commutation characteristics of the transfer switch under interrupting current of DC 4kA were studied. The calculated arc current and voltage were compared with the experimental results. Oscillation frequency of arc current in the experiment and simulation were 3 450 Hz and 3 759 Hz, respectively. Secondly, the influence of reactor and capacitor of the commutation path on the current oscillation process was investigated (L and C are 0.8 and 1.2 times of their typical values). Relationship between the radius, temperature and pressure of the arc and the current commutation characteristics was discussed. Finally, considering that air is a low-cost and environmentally friendly gas, arc characteristics of transfer switches in SF₆ and air were analyzed and compared. It is found that the simulation results are partially verified by the experimental results. Increasing values of reactor or capacitor can enhance the arc oscillation, accelerate the current commutation, and then narrow down the arcing time. As the resonance frequency is the same, the reactor has a much greater influence on the oscillation process than capacitor. Compared with SF₆, arcing time in air is shorter (reduced by about 4.5 ms), and peak voltage over capacitor in air is lower (decreased from 4 086.6 V to 2 760.5 V), which makes air applicable to transfer switches. In addition, it is expected that the simulation method could be applied to parameters optimization of transfer switches.