Study On Space Charge Measurement And Numerical Simulation Technology In Cable Insulation Under AC And DC Electric Field

Cross-linked polyethylene(XLPE)cable is an important part of the power system,which is widely used in AC and DC transmission and distribution networks.The accumulation of space charge will distort the internal electric field of the insulation,accelerate the insulation aging,and even break down in severe cases,affecting the service life of the cable.In this paper,the space charge characteristics of the coaxial cable insulation are studied by both experiment and simulation,and the assessment and detection method of space charge in cable insulation is improved.Compared with the traditional film structure using slicing method,the coaxial structure measuring system can obtain the space charge distribution in the cable insulation more comprehensively.In this paper,a coaxial structure space charge detection system that can be used under AC and DC stress is successfully developed.The measurement electrode module is improved.The pulse sources have two different coupling methods,which expand the application range and improve the flexibility of the detecting system.Based on this,two schemes are designed to obtain high-quality space charge measurement for cables with different thicknesses.The thicknesses of the measured cables range from 2.4 mm to 22.4 mm and the highest DC voltage reaches 320 kV,verifying the reliability of the detecting system.Under AC stress,the coaxial structure measurement system is based on the automatic equipartition phase shift principle,which can realize equalization and automatic phase shifting with a phase resolution up to 1.79° without setting phase detection and synchronization module.The space charge distribution in the cable insulation under different electric field shows that the long-term stability of the system.Through the two phase identification analysis modes proposed,the interference caused by the frequency fluctuation of the electric field are effectively solved.The coaxial structure space charge measurement results of two thinner cables(range from 2.4-4.0 mm)show that for different thickness model cables doped with nanometers,heterocharge accumulation occurs near the electrode under high electric field.During the volt-off procedure,the charge distribution characteristics show a high consistency,which is manifested by the accumulation of heterocharge near the electrodes.For cables with different aging modes,the space charge distribution characteristics is different.Under volt-on conditions,the water-aged cable has the most space charge accumulation,followed by the water-aged cable and the high-temperature-aged cable.Under volt-off conditions,the unaged cable has the most space charge,the water-aged cable is the second,and the high-temperature-aged cable is the least.A carrier transport model modified for the coaxial structure is carried out and the Poisson equation,the transport equation and the continuity equation is solved,by which space charge distribution in coaxial sample is calculated.The model is used to simulate the space charge under AC or DC electric fields.The comparison between the experiment and numerical simulation results shows that the model can simulate different types of charge accumulation trends,and shows a high consistency with the experiment results,which proves the feasibility of the numerical simulation model.