Research Of Insulation Defects In ±320 KV Flexible DC Cable Termination

Flexible DC has significant advantages in renewable grid-connected energy,island power supply,capacity expansion of urban power supply and so on,which received increasing attention.Currently,both at home and abroad the most common used flexible DC transmission line is DC cross-linked polyethylene(XLPE)cable.DC XLPE cable accessories(middle joints and terminations)are important component,and also the parts which are most likely to break down because of insulation defect.DC XLPE cable line has been applied for a short time at home and abroad,and research on how to apply existing insulation defect monitoring methods for XLPE cable under AC condition to XLPE cable under DC condition is scarcer at home and abroad,which deserves more study.This paper is based on projects from Fujian power company of State Grid: Research on Operation and Maintenance Procedures and Maintenance Strategy of Flexible DC Cable for Super High Voltage,to preliminarily analyze electric field distortion and the characteristics of partial discharge of ±320kV flexible DC XLPE cable insulation defects,providing a reference for the operation and maintenance of flexible DC cable lines.The main contents of this paper are as follows:1,With the help of the power supply corporation and cable manufacturers,carry out investigation,collect data,summarize insulation defects XLPE cable may exist,and set bubbles and impurity dopants as two typical insulation defects to be applied in finite element calculation and experiments.2,Refer to related domestic and international documents,to summarize insulation detection principle and characteristics of XLPE cable under current AC voltage,to present suitable insulation detection methods for XLPE cable under DC voltage.Analysis shows that the DC partial discharge can examine insulation defects well of XLPE cable under DC voltage.3,Use simulation software COMSOL to work out finite element calculation on ± 320 kV flexible DC cable termination composite insulation interface with no defects and existing bubbles or impurities,to research electrical distribution features existing defects of cable termination composite insulation interface,to obtain electrical strength varying pattern led by the difference of defects size and location,to provide theoretical basis for electrical effect of cable operation and maintenance state assessment.4,Set up DC cable lines of ±320kV cable body and its termination in the laboratory,from the experimental point of view,perform on-site simulation air-gap defects experiments on 320 kV flexible DC cable termination,study on period laws of partial discharge under DC voltage,to provide some reference for the operation and maintenance inspection.