Study Of The Cable Space Charge Measurement System Under AC Stress

The Cross-linked polyethylene power cables have been widely used in modern power system for its excellent mechanical and electrical performance. However, the polyethylene materials may age while cable operating, causing formation, accumulation and migration of space charge, which may change their dielectric properties and even cause cable insulation breakdown. Therefore,how to detect the insulation defects and latent faults of cables timely and effectively, avoid sudden fault caused by power supply interruption of the malignant cable accident is of great importance for power system reliablity.Electroacoustic pulse method (PEA method) is one of the most widely used methods around the world.There is much of literature about research of space charge measurement and distribution characteristics of the XLPE insulation film, section and coaxial cables under direct current(dc) stress, but no one is about alternating current (ac) stress in domestic so far. Most XLPE cables operate under ac stress, what’s more, the aging mechanism of XLPE cables under ac stress is different from that under dc stress. Therefore, researching the space charge distribution characteristics under ac stress in the XLPE cable insulation is of great significance.The paper presents the design of the XLPE cable space charge measurement system under ac stress and study the space charge distribution characteristics of domestic10kV XLPE cable, and the results are compared with these of relevant literature.Test results show that, the interface charge and the space charge distribution varies with the phase of ac voltage.For all the phase measured, there is almost no space charge accumulation and migration in1OkV cable under its phase voltage—5.8kV, and only the interface charge can be measured between XLPE insulation and electrode. Both the amount of the interface charge and that of space charge under23kV ac electric field is much than that of5.8kV ac electric field. Almost no interface charge and space charge at45°and225°, while at the amount of the interface charge and the space charge at135°and315°is maximum. What’s more, there is negative charge at135°and postive space charge at315°nearby lower electrode.