Characteristics Of VFTO And Study On Its Influencing Factors Under The Condition Of Novel Arc Model

In recent years, Gas Insluated Switchgear has been widely implemented in the electrical power network. However, the electric equipment is easily caused fault by very fast transient over-voltage (VFTO), with the enhancement of rated voltage, due to the operation of disconnector above 330kV GIS. Therefore the phenomenon of VFTO must be taken into consideration during the project of GIS in the UHV and EHV system.In order to accurately analyze VFTO, it is essential to find the equivalent models of each individual GIS component, especially the arc model of disconnector. According to the distributed parameter theory, the arcing physical process and two common arc models in the nowadays, a novel arc model, including three stages: prebreakdown, arcing and extinguishing, is proposed in the study. Moreover base on a 550kV GIS and utilized the FORTRAN language and MATALB program, the variation of VFTO is studied with different arc models. It is indicated that the physical process of arc is modeled precisely by the novel arc model and the VFTO peak values and frequency distribution are varied with different arc models. It is also practical method for the VFTO calculation.Secondly, the double-break circuit breaker is modeled as the distributed parameter model to study the VFTO on shunted capacitors on the basis of long-time (20min) arcing caused by the disconnector operating. Meanwhile the thermal effect of VFTO to shunted capacitors in circuit-breaker is analyzed and the influence of closing resistance in circuit breaker is discussed. The results demonstrated that the VFTO distribution on shunted capacitors of breaker is different and the shunted capacitors may be heavily damaged by the thermal effect of VFTO. The VFTO can be inhibited by the closing resistance in the circuit-breaker.In the last part, the paper presents the VFTO simulation of 1100kV GIS in China. And the inhibition of the on-and-off resistance installed on the disconnector and the metal oxide surge arrester is deliberated. Besides the VFTO restraining measures are suggested to ensure normal running of GIS.