Research On Key Issues Of Simulation For Very Fast Transient Overvoltage

Very fast transient over-voltage (VFTO) is produced when the disconnector operates in gas insulated switchgear (GIS), which may endanger the safety of the insulation of GIS equipment in ultra-high voltage(UHV) grid. The simulation technology is a important research method for obtaining VFTO waveforms and studying the characteristics of VFTO. In this dissertation, several key problems in VFTO simulation analysis such as modeling residual charge voltage on transmission lines, the simulation for repeated-breakdown VFTO waveforms and arc impedance model, are carried out to be analyzed and studied deeply. The principal content and achievements of this dissertation is listed as following:1. A novel simulation calculation method for single-breakdown VFTO waveforms based on time domain finite element method (TDFEM) is presented. Compared with the traditional electro-magnetic transient program (EMTP), this method not only can take the distribution characteristic of the residual charge voltage of the transmission line into account effectively, but also can calculate the discrete voltage and current values at any point along the transmission line. The simulation of single-breakdown VFTO waveforms is carried out by TDFEM and EMTP. The detailed comparative analysis is conducted on simulation results, demonstrating the effectiveness and superiority of TDFEM.2. A simulation calculation method for repeated-breakdown VFTO waveforms is presented. In this method, the influence of operating speed of disconnectors and residual charge voltage on repeated-breakdown VFTO waveforms is taken into consideration. The simulation of repeated-breakdown VFTO waveforms under a common situation is carried out by the proposed method. The characteristics of repeated-breakdown VFTO waveforms such as the times of breakdown, breakdown time, etc is obtained.3. The detailed comparative analysis is conducted on the arc impedance models of disconnector. The key arc parameters, which are inconvenience for measurement, such as breakdown delay, arcing resistance, arc resistance model, extinction time, the arc inductance and capacitance fracture, are obtained, laying the foundation for the research of the influence of the arc impedance model and its parameter of disconnector on VFTO. 4. The influence of the arc impedance model and its parameter of disconnector on VFTO is studied. The simulation results show that gas breakdown process has a great effect on VFTO gradient, steady state arc resistance influences VFTO amplitude and the quenching process of arc affects VFTO attenuation speed. Arc inductance and fracture capacitance can affect the maximum amplitude of VFTO and the waveforms trend.The subject of this dissertation received Natural Science Foundation of Hebei Province (Reaearch on Simulation Disconnect Switch Model for VFTO with Multi-Restrike E2012208006).