Safety Assessment Of A 1100kV GIS Shell With Defects

GIS is a kind of advanced high voltage power distribution equipment.Due to compact structure,high reliability and convenient installation,it is widely used in the construction of UHV power grid.In engineering practice,the crack,leak,deformation and other instability failure accidents about GIS shell occur frequently.It is easy to affect the electrical system and lead to economic losses.Through the testing about the scene and material,the actual environmental load and material properties are obtained to assess the safty of the shell.The actual environmental load was measured on the working condition by thermocouples,strain gauges and electronic digital micrometers.The change rule of the temperature,stress,axial displacement and bending angle was gained under the solar radiation.Based on the analysis of the testing data,the result was reached that great effect of solar radiation had been discovered on the temperature and the deformation of the shell.The temperature rose sharply at the top of the shell,it was 10?hotter than the bottom,the temperature was symmetrical on both sides.During afternoon,the temperature of the shell decreased fast with the decreasing solar radiation strength.Then all testing point temperature trended to be the same as the air temperature and change along it.The maximum amount of stress change near the defects was about 15MPa.Because of the temperature change of the shell,deformation emerged result from expand with heat and contract with cold.The deformation range of the shell along axial direction reached 0.973mm throughout the whole day.The sliders and expansion joint ran normally.The local temperature and its change at the shell were different,which induced the heterogeneous deformation in the shell.Bend deformation was observed,on the flange section at the end of the shell,the deviation angle of0.01°was measured.It was revealed that the temperature,stress,axial displacement and bending angle changed periodically,and their frequencies were both once a day.Weld specimens were made of the same material and manufacturing process as the GIS shell.The properties including tensile,fracture toughness and fatigue crack growth of the base material and the welds were measured.The tensile strength and yield strength of base material are not related to the direction,the yield strength of welds is close to base material,but tensile strength is lower.The average fracture toughness of base material is about 47.91 kJ/m~2,the average value of welds is about 46.79 kJ/m~2.Due to the uneven organization of welds and possible defects,fracture toughness of welds has greater discreteness.The fatigue crack growth rates of base material and welds are approximately the same.By comparing and demonstrating the safety of three failure assessment curves in R6,Safety assessment and fatigue life prediction were carried out on the defects by the normal method based on GB/T 19624-2004.The assessment result showed that the GIS shell containing defects is safe under the current load condition.The fatigue life of the defect in the left shell is about 6971 cycles,failed to meet the design life,and the fatigue life of the defect in the right shell is about 37915 cycles,met the design life.