Study On Insulation Characteristics Of GIL And Its Insulation Optimization

Gas Insulated Metal Enclosed Transmission Line(GIL)with the merit of large capability,flexible layout,low impact on or of environment,can be used in those situations which the climatic environmental is formidable or the corridor is limited. However,the dielectric strength of SF₆ is extremely sensitive to the nonuniformity of the electric field,and the polarity of DC nonuniform electric field is obvious. After the DC voltage applied on insulator,the surface discharge and the metal conducting particle accumulated or attached on the insulator can both reduce the flashover voltage.As a result,application and development of DC GIL is limited by these reasons.So having studies of SF₆ gas gap's breakdown characteristics and insulator flashover characteristics,which are used in DC GIL,can do helps for understanding the mechanism of DC gas gap discharge and DC insulator flashover, and can solve the key technologies of GIL insulation design.This thesis works on the insulation characteristics and insulation optimization method of DC GIL.First,SF₆ gas discharge theory and its breakdown characteristics in various electric fields are introduced.Next,a DC GIL insulation tester is developed for SF₆ gas gap insulation test,insulator flashover test and metal conducting particle test.SF₆ gas gap insulation characteristics of eccentric cylinder in positive and negative DC voltage are also studied by using this insulation tester. Then,based on the international test results of small-scale electrode and considering the surface roughness,the equation which can be used for estimating the critical breakdown field is deduced by using Levenberg-Marquart method.And by means of analyzing the impact of surface charge accumulation and free metallic conducting particles on surface discharge of insulators,it is pointed out that the surface charge accumulation and the adhesion of free metallic conducting particle are key reasons causing insulation performance deterioration of DC GIL.At last,the DC GIL electrode which includes particle trap,particle driver and field-well ring is designed. Electric field distribution of this electrode is also emulated.All the work this thesis introduced provides experimental fundation for various insulation test investigates of DC GIL insulation characteristics.Suppression methods for surface charge and metal conducting particle of DC GIL is brought forward.And it is also can be tooken as the basis of insulation design and application for DC GIL.