Calculation on the Transient Circulating Current of GIS Enclosure Caused by DS Operation Based on the Exponential Reignition Model of SF6 Gas Discharge

To clearly understand TCC (transient circulating current), which is one of the most important EMI (electromagnetic interference) source of GIS (gas insulated substation), a research about TCC is carried out. The generation mechanism of TCC is analyzed, and a current transformer coupling method to calculate TCC accurately is presented. Then, this paper focus on setting up the model of SF6 gas discharge, which is the key problem of calculating TCC. According to the impedance variation characteristic of SF6 gas discharge, an exponential reignition model is set up and the typical transient parameters such as amplitude, rise steepness, duration, decay time and frequency are calculated. The results show that: 1) The positive and negative maximum value of TCC with UHV(ultra-high voltage) voltage level is about 129.90 A and -108.37 A respectively, and the positive value of TCC is always larger than that of the negative; 2) the rise steepness of TCC waveform can reach 321.39 A/μs, the duration and decay time is about 12 ms and 24.32 μs, respectively; 3) the frequency of TCC distributes at the range of 0~417 MHz, and the dominant frequency is 5~20 MHz and 30~35 MHz.