| Gas insulated substation(GIS,Gas Insulated Substation)is widely used in high voltage grade power system in China because of its excellent performance.The fast transient overvoltage(VFTO,Very Fast Transient Overvoltage)phenomenon occurs due to the slow motion speed of the contact and the absence of the arc extinguishing device during the operation of the GIS disconnector,and the accurate isolation switch arc model is the key to the simulation VFTO.For the purpose of studying the causes and influencing factors of VFTO,this paper will study from the following aspects:1.Analysis and comparison of existing arc models.In this paper,the arc model is studied from three stages: pre-breakdown,steady-state combustion and arc extinguishing.the range of arc resistance variation of exponential time-varying arc model,Toepler spark arc model and hyperbolic arc model in pre-breakdown stage is compared.The problems existing in exponential time-varying arc model and Toepler arc model are summarized,and the feasibility of hyperbolic arc model as arc pre-breakdown stage model is verified.The progress of the double exponential time-varying arc model and the shortcomings of the segmented arc model are pointed out.2.The multiple reburning arc model of isolating switch is established.Based on flow injection theory and Pedersen gas breakdown criterion,the breakdown process of arc is analyzed,and the criterion of gap breakdown is summarized.Based on the theory of arc gap medium recovery and energy balance,the arc extinguishing is divided into two stages.The criterion of arc extinguishing is summarized.The repeated reburning process of arc is simulated based on the criterion of arc breakdown and extinguishing.The simulation results are compared with the experimental waveforms to verify the feasibility of the simulation model.The VFTO waveforms of multiple positions in the GIS are compared,the causes of the VFTO step change on the load side of the disconnector are analyzed,the causes of the peak overvoltage in the VFTO are summarized,and the reasons for the higher amplitude of the bus terminal VFTO are discussed.3.Explore the influence of arc parameters on VFTO characteristics.The influence of arc parameters such as breakdown delay,steady-state arc resistance and arc extinguishing time on VFTO characteristics is studied in this paper.The results show that when the breakdown delay increases,the VFTO breakdown steepness of each key position in the GIS decreases to varying degrees.when the steady-state arc-burning resistance increases,the VFTO extreme value will appear obvious attenuation,and the effect on the bus end is the most obvious.Arc extinguishing time changes will affect the duration of VFTO shocks.4.Studied the influencing factors of VFTO.the influence degree on the VFTO is analyzed through multiple sets of data from three aspects: the residual voltage on the load side,the length of the GIS line and the phase of the supply voltage during the operation of the disconnector.The results show that the breakdown times and the breakdown amplitude of the disconnector gap will be affected by the residual voltage on the load side.The increase of GIS line length will make the VFTO extremum irregular.Change of voltage phase angle will affect the duration of VFTO oscillation. |
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