Assessment And Rejuvenation Of XLPE Power Cable Insulation

XLPE power cables are widely used in power plants, substations, industrial and mining enterprises and urban distribution system. Breakdown accident has occurred frequently in early operation cable because of the insulation aging, and show an upward trend year by year. This situation is a serious threat to the safety of power system. In order to ensure the safety of power grid, the aged cable will be replaced. However, a lot of manpower, material and financial resources will be wasted by replacement, and the project of replacement also will be very difficult. Therefore, the cable insulation is considered to be repaired before the development from water trees to electrical trees. Then the service life of cable will be improved, the running cost of power system will be saved, and the safety of power grid also will be improved.Simulation models of tubular water tree, butterfly water tree, normal cable terminal and a cable terminal increased a repair joint had been established based on the actual shape of water tree and cable terminal. A finite element software Ansoft was used to simulate all above models. The electric field of the tip of the tubular water tree and butterfly water tree in different lengths and widths were studied. The electric field distributions of the tubular water tree and butterfly water tree before and after the rejuvenation were compared. The electric field distribution of a normal cable terminal and a cable terminal increased repair joint were simulated. The thickness of semi-conductive tape on the repair joint was determined.Based on the Debye model of transformer, a new cable Debye model with a water tree section RC circuit was established. The ratio spectrum of cables with different water tree lengths and areas were calculated by ratio spectrum theory and cable Debye model. A map of maximum value of the ratio spectrum was used to assess water tree in cable insulation. At last, an experiment was designed to verify the reliability of the ratio spectrum assess the water tree in cable insulation.The breakdown voltage tests of unrepaired cable and cables repaired with PhSi(Me)-(OMe)2, Me2Si(OMe)2, Me3Si(OMe) were contrasted. The characteristics of water tree growth for unrepaired cable and cables repaired with PhSi(Me)(OMe)2, Me2Si(OMe)2, Me3Si(OMe),70%PhSi(Me)(OMe)2/30%Me2Si(OMe)2and70%PhSi(Me)(OMe)2/30%Me3Si(OMe) five rejuvenation liquids were studied. The spread characteristics of cables repaired with PhSi(Me)(OMe)2,70%PhSi(Me)(OMe)2/30%Me2Si(OMe)2and70%PhSi-(Me)(OMe)2/30%Me3Si(OMe) were tested. Rejuvenation liquid injection system was designed.The cable was repaired by70%PhSi(Me)(OMe)2/30%Me3Si(OMe) mixed rejuvenation liquid. The dielectric loss, insulation resistance, DC leakage current, ratio spectrum of cable were tested before and after the cable rejuvenation. Density distribution of different length butterfly water trees in repaired and unrepaired cables insulation were tested to compare the rate of cable water tree generated for repaired and unrepaired cables.