Study On Power Frequency Breakdown Characteristics Of Parallel Wires With Insulation Sheath

In recent years,air gap breakdown of transmission lines frequently occurs as compact transmission line technology has been widely used and various disaster weather increases gradually.Air gap power frequency breakdown accident is a major potential security risk for power system operation.Moreover,since transmission line reclosure is not easily achieved,the safety and stability of power system operation is severely affected,and heavy economic loss is caused.Now the research on air gap power frequency breakdown of high voltage transmission lines in domestic covers windage yaw,ice coating,rainfall,forest fire,dense fog and so on,and also includes related breakdown theories,models and experiments of towers,insulator chains,wires,wire jumpers,etc.However,related technologies of the new wire insulating coatings and sheath to control the air gap power frequency breakdown of high voltage transmission lines are seldom adopted.For the case mentioned above,the research idea and method of improving air gap power frequency breakdown voltage by wrapping insulating sheath on transmission lines is proposed.The test model of parallel wires wrapped in an insulating sheath is designed,and power frequency breakdown test is conducted for different insulating sheathing materialsand different wrapping ways.The air gap power frequency breakdown phenomena of wires wrapped insulating sheath are recorded,and the effect of wrapping insulating sheath on improving air gap power frequency breakdown voltage is analyzed comparatively.Four different insulating sheath materials are used for the test,and electric strength tests are carried out respectively for the discussion on electrical characteristics of those sheath materials.For studying the enhancement of breakdown voltage after wrapping insulating sheath visually and conveniently,the power frequency breakdown test of bare wires is conducted for comparison,in which the relationship of power frequency breakdown voltage of bare wires and wire distance is investigated.The result shows that the voltage increases almost linearly along with the wire minimum distance increasing,and average breakdown field intensity decreases as the wire distance increases.The power frequency breakdown test of parallel wires wrapped in insulating sheath is conducted,in which several situations such as parallel wires wrapped in a single insulating sheath,parallel wires wrapped in double insulating sheaths,parallel wires wrapped in insulation coating and so on are included.The promotion effect on wires insulation characteristics is discussed and the effect of different wrapping ways on improving the power frequency breakdown voltage is analyzed comparatively from the view of safe distance.The simulation calculation of power frequency breakdown electric field of wires in a short gap distance is conducted by software Comsol Multiphysics,and the reason for improving the air gap breakdown voltage of bare wires by wrapping insulating coatings and sheath is analyzed from the view of electric field.In addition,the model of wires wrapped in insulating sheath is expressed by chain equivalent circuit,which depends on the ways and structure of wrapping insulating sheath on wires and the sliding discharge phenomena in the test.The surface sliding discharge of parallel wires coated with insulated sheath is explained in virtue of the model.