Study On The Mechanism And Application Of Supressing Very Fast Transient Overvoltage By Optimizing The Switching Speed Of Disconnector

During the process of disconnector operation in gas insulated switchgear(GIS),repeated strikes occur and result in very fast transient overvoltage(VFTO),which threatens the insulation of the GIS equipment.The installation of damping resistor in disconnector is the main mitigation measure of VFTO in current engineering projects.It can effectively limit the amplitude of VFTO and reduce the frequency of VFTO.However,damping reisitor also makes disconnector with bigger size,more complex structure and higher cost.When choosing mitigation measures of VFTO,the characteristics of disconnector as well as the distribution characteristics of VFTO are generally ignored.It results in that the VFTO mitigation measures might be too conservative and not economical.The switching speed of the disconnector has a great influence on VFTO.Suppressing VFTO by optimizing the switching speed of disconnector avoids the installation of the damping resistor or other equipments and can improve the economy and reliability of the engineering project.In this paper,the mechanism and application method of supressing VFTO by optimizing the switching speed of disconnector were studied.The simulation method for probability distribution characteristic of VFTO during disconnector swithcing was studied.The simulation models of UHV(Ultra High Voltage)GIS equipment for VFTO were given.The repteated striking process of disconnector switching was analyzed.The factors influencing the probobality districution characteristics of VFTO were analyzed.The simulation method of VFTO probability distribution characteristics during disconnector swithcing was proposed.The probability distribution characteristics of VFTO and residual voltage during disconnector switching were obtained by simulation.The simulation results and the measured results were compared.The validity of the VFTO probabality distribution characteristic simulation method is verified.By performing a mathematical description of the disconnector switching operation,the influence of the operation speed of the disconnector on the residual voltage and VFTO duiring the repeated striking process was studied.The influence mechanism of the disconnector switching speed and the polarity of the breakdown voltage on the disconnector switching was revealed.The control condition of the disconnector speed to supress VFTO was proposed.The influence of the disconnector characteristics on the VFTO was simulated.The probobality distribution characteristics of VFTO and residual voltage under different disconnector characteristics were obtained.Simulation results are in accordance with the theoretical analysis.Test of UHV GIS disconnector with adjusting switching speed were carried out.The simulation results are compared with measured results.The theoretical analysis is verified by both simulaiton and test.The effect and application method of adjusting the disconnector speed to supress VFTO were studied.The optimal value of the switching speed of the disconnector is proposed according to current UHF GIS disconnector.The selection method and flow of VFTO suppression measures considering disconnector characteristics are proposed.For an actual substation,study on VFTO suppression measures was carried out.The results show that it is helpful to avoid unnecessary suppression measures after considering the characteristics of disocinnector and VFTO distribution.