High Voltage Frequency Domain Dielectric Spectrum Properties And Diagnosis For Water Intrusion Defects Of XLPE Cable

XLPE power cables are widely used in urban power grids.They are easy to cause water intrusion during production,transportation,laying,and operation,forming water intrusion defects.Water intrusion defects include damage to the outer sheath of the cable,water ingress defects of the core,water ingress defects of the joints,and water tree aging defects,and the degree of damage varies.Timely detection and diagnosis of different types of water intrusion defects are of great significance to the safe operation of XLPE cables.The traditional 0.1 Hz ultra-low frequency method only evaluates the state of the cable,and cannot distinguish the types of defects,and the detection sensitivity for local defects is insufficient.Four types of water intrusive defective cables are designed and prepared,including damaged water in the outer sheath,water in the core,water in the joint,and water tree aging.The defective cable is detected by the method of high voltage frequency domain dielectric spectrum and analyzed.The characteristics of the high voltage frequency domain dielectric spectrum,the curve layering degree S and the hysteresis degree D are extracted as the characteristic parametsers of the high voltage frequency domain dielectric spectrum,and the diagnosis and evaluation of different water intrusion defects of the cable are carried out,the detection sensitivity is compared with the traditional 0.1 Hz ultra-low frequency method.The research results show that:the 0.1 Hz ultra-low frequency method detects water intrusive defective cables as an attention state,and cannot distinguish the types of defects.The high voltage frequency domain dielectric spectrum extracts the stratification degree S and the hysteresis degree D,which can effectively distinguish and diagnose the type of water intrusion.Local defects of long cables cannot be detected by ultra-low frequency,and the sensitivity is low.The high voltage frequency domain dielectric spectrum shows increasing changes at high voltage and low frequency.The sensitivity of defect detection is affected by the proportion of water intrusion length,water intrusion time and type of water intrusion.The lower the percentage of water intrusion length and the shorter the water intrusion time,the lower the sensitivity of detection.The detection sensitivity of the damaged water intrusion defect of the outer sheath is low.