1100kV GIS中VFTC的暂态特性研究

Study on Transient Characteristics of VFTC in 1100 kV GIS Substation

GIS隔离开关操作所产生的特快速暂态过电流（VFTC）不仅对GIS设备绝缘具有极大的破坏性,还会对二次设备造成严重的电磁干扰。但现有的研究多集中于暂态过电压（VFTO）,而忽略了VFTC的研究。针对这一现状,开展了特高压等级VFTC暂态特性的研究。因隔离开关操作条件下SF6气体放电特性决定了VFTC的暂态特性,首先分析了SF6气体的放电特性,讨论了SF6气体不同放电阶段的阻抗变化规律,在此基础上采用分段原则建立了新型SF6气体高频放电模型。利用该新型SF6气体放电模型对某特高压GIS变电站的隔离开关操作所产生的VFTC波形进行了仿真计算。为研究VFTC的暂态特性,定义了VFTC的衰减时间常数,讨论了隔离开关加装阻尼电阻对VFTC暂态特性的影响。研究结果表明：特高压等级的VFTC有幅值高（可达几千安培）、频率高、主频分布宽（0~25 MHz）、衰减长（100 μs左右）等特点。加装阻尼电阻可大大提高VFTC的衰减速度,有利于VFTC的抑制,但阻尼电阻对主频分布影响较小。

The very fast transient current（VFTC） occurring in GIS is mainly caused by SF6 gas discharge due to disconnector operation. This phenomena will not only destroy the insulation of GIS equipment, but also cause a series of electromagnetic interference problems on the secondary equipment. However, current research mostly focuses on very fast transient overvoltage（VFTO） and ignores the effect of VFTC. Transient characteristics of VFTC in UHV（Ultra High Voltage） level are studied. A segment model is adopted in high frequency discharge model of SF6 based on impedance change in different discharging stages. This new model is applied to simulate VFTC during disconnector operation in a UHV GIS substation. For better understanding the transient characteristics of VFTC, decay time is defined to describe VFTC transient characteristics. Restrain effect of damping resistor on VFTC is also discussed. From research results, VFTC under UHV level has characteristics of high amplitude（up to several thousand amperes）, high frequency, broad dominant frequency distribution （0~25 MHz） and long decay time（100 microseconds）. The damping resistor can greatly improve VFTC decaying rate, but has small influence on distribution of dominant frequency.