| GIS is the abbreviation of gas insulated switchgears which filling SF6 as insulating medium.Because of its excellent arc extinguishing ability,it is widely used in the field of EHV and UHV power transmission.As well as the SF6 insulation medium with strong arc extinguishing performance,there are many solid insulation mediums such as supporting insulators in GIS.The permittivities of these insulating materials are characteric by different dielectric properties under high-frequency voltage.Therefore,accurate simulating model of overvoltage is the key to analyze accurately the insulation performance of GIS.Firstly,the 800 kV GIS is taken as the researched object in this paper,and the the simulation model in ATP-EMTP is established based on specific operating mode.In the process of overvoltage simulation,it not only takes the influence of the incoming bus and overhead lines into account,but also takes the influence of different lightning locations into account in GIS equipments.The aims are to find out the most serious lightning situation of equipment.Secondly,considering the effect of arc model on very fast transient overvoltage,the arc model is established based on the Mayr-Schwarz arc equation in ATP.At the same time,the test circuit that charging disconnector and bus in 800 kV GIS is simulated.The results show that the arc resistance model used in this paper can better reflect the physical process of arc reburning.The waveforms of VFTO on the typical locations are compared in GIS,and the change regularity of amplitude and frequency of overvoltage in different position are analyzed.Meanwhile,according to the calculated power frequency overvoltage and lightning overvoltage,the electric field distribution between the disconnector contacts is simulated.Compare the value and location of the maximum field strength.Under the steep front-wave overvoltage,the electric field distribution along the surface of the disconnector and the surface of the shield is further analyzed.By comparing the values of tangential field strength and normal field strength,the dangerous location of insulation has been found.All of results will provide the data basis for reducing the probability of surface discharge.In the end,aiming at the frequency characteristic of the steep front-wave overvoltage,the permittivity of the dielectric can be changed obviously when the frequency component is active in the insulating medium.The permittivity of the insulating medium is calculated by mathmatical duduction,and the distributions of electric field strength under different frequency components are also simulated.It will provide the theoretical basis for insulation optimization of UHV power equipment. |
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