负极性直流电压作用下SF_6气体中极不均匀电场局部放电特性研究

Study on Partial Discharge Characteristics of Severe Non-uniform Electric Field in SF_6 Under Negative DC Voltage

随着特高压直流输电技术(HVDC)的发展,以SF_6作为主要绝缘介质的直流气体绝缘输电线路(GIL)受到越来越多的关注和研究。直流GIL中金属尖端缺陷会造成局部电场集中,引发局部放电,因此研究直流电压作用下SF_6气体中极不均匀电场局部放电特性可为直流GIL的建设提供试验依据,具有重要意义。通过搭建负直流高压局放试验平台,研究了SF_6气体中气压、电场不均匀系数对起始放电电压(PDIV)的影响,并分析流注发展过程的放电特性。结果表明:随着气压的上升,PDIV增加,尖端曲率半径较小时,SF_6气体对气压敏感程度随气压上升而增加,尖端曲率半径较大时SF_6气体对气压敏感程度随气压增加而减小;随着电场不均匀系数的增加,PDIV减小,低气压下,SF_6气体对电场不均匀程度敏感性较大,且随电场不均匀系数增加而降低,高气压下,SF_6气体对电场不均匀程度敏感性较小,且随电场不均匀程度增加,敏感程度降低;放电过程可分为放电起始、流注发展和间歇击穿3个阶段。

With the development of HVDC technology,the DC gas insulated transmission line(GIL)with insulated SF6 is increasingly focused on.The metal tip defect in GIL will result in partial electric field concentration and lead to partial discharge(PD).Therefore,it is of great significance to investigate the PD characteristics of metal tip defects to provide an examination basis for the development of DC GIL.Based on the half-wave rectification principle,we set up a DC high voltage test platform and discussed the influences of SF6 pressure and coefficient of electric field inhomogeneity on the PD characteristics,and then studied the characteristics of PD development process.The results show that increasing SF6 pressure can increase the partial discharge initial voltage(PDIV),and the sensitivity of SF6 to gas pressure increases with the increase of SF6 pressure with small tip radius,and on the contrary,the sensitivity of SF6 to gas pressure decreases with the increase of SF6 pressure with relatively larger tip radius.Besides,increasing tip radius can decrease PDIV,SF6 is more sensitive to electric field inhomogeneity in low pressures and less sensitive to electric field inhomogeneity in high pressures,and the sensitivity decreases as the electric field inhomogeneity increases whatever in high or low SF6 pressures.The PD development process can be divided into 3 stages,including PD initiation stage,circulation development stage,and intermittent breakdown stage.