Research On Aging And Breakdown Characteristics Of 160kV HVDC Cable Insulation Material

Because of the excellent mechanical and electrical properties,XLPE cable is widely used in HVDC transmission system.The XLPE insulation degradation will occur during the operation,which will lead to the accumulation of space charge.The accumulation,transfer and disappear of space charge will lead to internal field distortion,which will affect the aging and breakdown characteristics of the XLPE insulation.Research on XLPE insulation aging characteristic is of great significance to HVDC transmission system.The XLPE sample is artificially accelerated aged on the condition of 90 ?(50d,100 d,140d),135 ?(30d)and electrical field 40kV/mm(15d,25d).Then,the accumulation,dissipation properties of space charge were studied by Pulsed ElectroAcoustic(PEA)method.The results showed thatthe total amount of space charge starts increasing after a period of reduction under thermal aging at 90 ?.While the total amount of space charge increases quickly under thermal aging at 135 ?.Besides,the aging mechanism of the samples was analyzed by Fourier Transform Infrared Spectroscopy(FTIR)and Differential Scanning Calorimetry(DSC).It shows that it leads to the increment of carbonyl group and reduction of crystallinity at 90 ?for a long time and 135? under thermal aging condition.The characteristics curves vary barely under electrical aging condition.At last,the breakdown property under impulse voltage is studied and compared with that under DC voltage of the XLPE sample under different temperature.The results shows that the temperature had little influence on the electrical breakdown property of XLPE insulation under lightning impulse voltage,which fluctuate between 215 k V/mm-240 kV/mm under 20 to 70 ?.While the breakdown strength under switching impulse and DC voltage decrease as temperature rise.