Research On Very Fast Transient Overvoltage Of 1100 KV GIS

With the rapid development of ultra-high voltage in China,the insulation characteristics and running status of 1100 kV gas insulated switchgear have gradually become the emphases of research.In the experiment of studying the insulation performance of 1100 kV GIS,the phenomena like breakdown of insulator prompted the tester to pay attention to the very fast transient overvoltage.Based on the phenomena and data of 1100 kV GIS experiment,simulation on the very fast transient process of 1100 kV GIS test loop has been carried out in this paper.In order to obtain the state of 1100 kV GIS in operation,the simulation continued to be conducted on the arc ignition of disconnecting switch in the main electrical wiring which is in 1100 kV substation during closing process.The main content of this thesis include:Firstly,the basic theory and simulation method of very fast transient overvoltage were researched.The operation of disconnecting switch is the primary cause of very fast transient overvoltage.Therefore,the generation principle of very fast transient overvoltage was analyzed by the operation process of disconnecting switch.In addition,the amplitude,steepness and frequency of the voltage waveform were described.Furthermore,the thesis analyzed and summarized the influence of very fast transient overvoltage on different transmission channels,like insulation breakdown.The equivalence principle of centralized and distributed elements was explained in the theoretical study of very fast transient overvoltage.Secondly,the phenomena in the experiment of 1100 kV GIS experiment were organized and summarized into three parts:The first part focused on the surface discharge of the insulator caused by the internal transient overvoltage.The second part involved were that the insulation breakdown of transformer and secondary equipment failure on account of the external transient overvoltage.The third part related the transient potential of 1100 kV GIS shell which was increased due to transient enclosure overvoltage.On the basis of theoretical research,a simulation analysis scheme for experimental phenomena was presented.Thirdly,the transient overvoltage simulation analysis of the 1100 kV GIS test loop was conducted.So the voltage level of the insulator at the connection between the bushing and GIS,transient overvoltage propagating to the transformer and the overvoltage propagating to the secondary side over the weakly damped voltage divider all can be captured.The experimental phenomena caused by transient overvoltage can be explained,too.According to the causes of transient overvoltage,the suppression scheme which is used to improve the installation process of GIS and increase the number of protection resistance was put forward.Fourthly,on the basis of the VFTO simulation results,the shell transient potential simulation analysis of the test loop was carried out by means of power equivalence.So that the voltage response of the shell transient loop under the excitation of the test voltage can be obtained and the method of grounding suppression was proposed to limit the lifting of shell transient potential.Comparing three kinds of grounding lines and grounding modes,it was confirmed that the most reasonable grounding scheme was to use copper foil to ground to the nearest,and copper braid wire was used to short-circuit the flange.Finally,on the basis of the establishment of equivalent model and selecting of loop parameters,launnching the single arcing simulation of main electrical connection in the UHV substation.Resistance is used to describe the insulation change of break gap during operation of disconnecting switch.The process of arc included three stages:arc initiation,arc burning and arc extinguishing.By adding control modules of are initiaftion and arc extinguishing to the transient simulation model of substation,the reignite simulation model of main electrical connection was established,and the arc ignition process in actual substation was obtained.The effect of closing resistance and ferrite magnetic rings to suppress the transient overvoltage was compared by simulation and the results verified the rationality of using closing resistance to suppress VFTO.