Study On The Critical Condition And Internal Defect Detection Of 220kV Composite Insulator On Live Work

Compared with porcelain and glass insulators,composite insulators have such prominent advantages as low quality,high strength,strong pollution flashover resistance and convenient maintenance,and have been widely used in power systems.The following faults were found during operation: mandrel breaking suddenly,surface hydrophobicity decreasing,internal insulation flashover and surface aging.It is difficult to find the defect of internal insulation conductive channel in appearance,but it is the most dangerous defect.Charged on110 kv ～ 1000 kv line operation is widely used,because of the composite insulator charged homework without access to relevant technical specifications and test method and device,insulator containing defects whether meet the requirements of charged operation safety,mainly through a visual inspection to determine,for inside the electrical conductivity of the defect and its effect on the electrical safety operation clearance is unable to evaluate,to live working at risk.Therefore,this paper focuses on the influence of defects of internal conductive channels on live work of composite insulators.On the one hand,the critical conditions of live work are determined through discharge test;on the other hand,the detection method of defects of conductive channels is explored through electric field simulation.According to the discharge test,the critical conditions for the live operation of 220 k V composite insulator are determined as follows:(1)when a section of conductive channel is defective and has the same potential as the high-voltage end,the remaining good insulation length shall not be less than: when the altitude is 0m,the good insulation length is 1.3m;When the altitude is 1000 m,the good insulation length is 1.5m.(2)when the conductive channel is at suspension potential,the discharge voltage of the combined gap is the lowest when the defect is 0.4m away from the high-voltage end,and the combined gap length shall not be less than: when the altitude is 0m,the combined gap length is 1.5m;When the altitude is 1000 m,the combined clearance length is 1.7m.It is found by field measurement that the surface field intensity of workers with equal potential is reduced by the appearance of defects.In 220 kv transmission line charged homework,live working personnel(including electric potential workers)shielding clothing wear Ⅰ type,can satisfy the provisions of China’s national standard GB6568.1-2000.Through a large number of simulation computation,a larger study and summarizes the composite insulator conductive channel electric field change characteristics of defect,and accordingly put forward the corresponding defect detection methods,the main conclusionsare as follows:(1)conductive channels connected to the high end,have more influence on the composite insulator string of electric field,the axial electric field "peaks" shape curve is obvious;The length of the defect can be determined according to the maximum position of the axial electric field curve,and the maximum error is half the length of the umbrella skirt.(2)when the conductive channel is at the intermediate suspension potential,the radial electric field curve and the radial electric field distortion curve have obvious reflection on this defect,which can be used to judge the length of the defect.The maximum error is an umbrella skirt distance.(3)if there are defects in two conductive channels,if the first one is connected with the high-pressure end and the second one is at the suspension potential,the first one can be detected by axial electric field curve,and the second one can be detected by radial electric field distortion curve or radial electric field curve.(4)when both defects are at suspension potential and the defect spacing is less than 5cm,the radial electric field distortion curve and the radial electric field curve will misjudge the defects as one segment;When the gap is more than 5cm and less than 15 cm,the radial electric field distortion curve can distinguish the defects in two sections,and the radial electric field curve will still be misjudged as one section.When the gap is more than 15 cm,both the radial electric field distortion curve and the radial electric field curve can distinguish two sections of defects and judge the length of defects.