±800kV直流穿墙套管耐压试验发生外闪原因分析及改进措施

Cause Analysis and Improvement Measure of ±800 kV DC Wall Bushing Occurring Flashover During Overvoltage Withstand Test

为找出某特高压直流输电工程中,其高压端阀厅直流侧800 kV穿墙套管在进行直流耐压试验过程中发生外闪的根本原因,并研究应对措施,通过结合现场试验实际情况,借助有限元算法对其进行分析。分析结果表明:由于该型特高压直流穿墙套管原均压环结构不合理,造成其表面场强分布极不均匀,尤其法兰与绝缘外套连接处电场强度过高,非常接近空气击穿场强,在其表面有一定污秽和湿度较大的情况下,借助960 kV特高压直流试验电压非常强的累积效应,就形成了贯穿性外闪放电。据此,提出相应的改进措施,即在该型特高压直流穿墙套管的法兰与绝缘外套连接处加装1个相同的均压环,并适当调整均压环的罩入深度。通过有限元算法对此措施进行验算,结果表明:采用这种改进措施会使得其外部场强分布得到根本性改善,大大提高其运行可靠性。

To find the reason why flashover occurs in the 800 kV wall bushing of high-potential valve hall during the voltage withstand test on-site of UHVDC project and to study the improvement measures.Combining the field test in practical situation,we analyzed the basic reason with finite element method.Results show that the structure of grading ring of this type UHVDC wall bushing is unreasonable so as to make the electric field distribution on surface non-uniform.Especially,electric field intensity of connection part between flange and insulation covering is very high which is very close to the breakdown field strength in air.Moreover,a very intense accumulative effect by applying 960 kV ultra high voltage DC（UHVDC） test voltage in high humidity and surface pollution condition will form the throughout discharge at last.Thereby,improvement measures are proposed： another the grading ring with same structure is added at connection part between UHVDC wall bushing flange and insulation covering,and the covering depth of grading ring is appropriately adjusted.The finite element method is used to check calculation,and the result indicates that the outside electric field intensive distribution is improved ultimately and the operation reliability is also greatly increased.