Study On The Dynamic Characteristics Of Space Charge In XLPE Insulation Under Pulse Electric Field

With the transmission technology development,high voltage power cable has been widely used in modern transmission system.Cross-linked polyethylene(XLPE)is widely used in cable insulation.During the long-term operation,space charges accumulate in XLPE insulation,leading to electrical tree aging and even breakdown.According the types of insulation breakdown accidents,the insulation breakdown is mainly caused after operation or lightning over-voltage.It is concluded that space charge is the fundamental cause of cable insulation breakdown in high voltage electric field,but the damage mechanism is still unknown.It is important to study the space charge characteristics under DC square wave electric field and analyze the amplitude space charge changes before and after the rising and falling edge.In this paper,author improved the space charge measurement method by designing pulse phase matching circuit for multi-period measurement,and the system can carry out multiple space charge measurements in a single period.After debugging the space charge test system and ensuring its normal operation,several pre-experiments were carried out to determine the field strength and the rising-falling time.Then,the space charge accumulation experiments were carried out under DC square wave electric field by selecting the cable insulation XLPE slice and the XLPE slice of granular material.The space charge waveforms before and after the rising edge and the falling edge were compared.The experimental results show that the heteropolar charge accumulated in the cable insulation XLPE slice,while the homopolar charge accumulated in the XLPE slice of granular material.The total charge in the XLPE slice of granular material decreased significantly with the time of pressing.Before and after the rising edge and the falling edge,the heteropolar charge peak amplitude in the XLPE cable insulation slice changed inversely to the voltage amplitude.According to the experimental results,the author puts forward the carrier force model under pulse electric field to explain the experimental phenomenon,and calculates the theoretical mobility of the carrier.The results are consistent with the experimental data calculation results.It is proved that there are a lot of carrier movements in the voltage mutation process,which is much more than the case under DC electric field.In the end,author puts forward the electric tree initiation model under pulse electric field and the cumulative effect of the pulse electric field on the damage to the insulation structure.The energy released by the charge behavior under pulse electric field will cause irreversible damage at the weak point in cable insulation,and eventually lead to the electrical tree initiation.It is very important to study the space charge behavior under pulse electric field for restraining the space charge in cable insulation,prolonging the cable life and optimizing the cable insulation manu-facturing process.