Rapid Detective Method For Water-tree Retardant XLPE Power Cables

Cross-linked polyethylene (XLPE) power cable is widely used in urbantransmission and distribution network, due to its excellent electrical performance andtransmission capacity, good heat resistance, easy to be bend and fixed. The electricalproperty of the XLPE insulation material is extremely advantageous in dry condition.However, the XLPE power cable will be deteriorated affected by factors of electricity,heat, moisture, mechanical stress and chemistry when it is put into operation.Particllarly, the water trees will initiate in insulation influenced by the combination ofelectric field and moisture. Once generated, the electric field strength will be focusedon the tip of water trees which finally convert into electrical trees. Electrical trees maylead to the insulation breakdown in short terms and be in accident, which seriouslyendanger the reliability of the power grid.The literature on water tree resistant method in XLPE insulation is vast. Thesestudies proceed in two major areas to inhibit the generation and development of thewater trees. One is to mix water tree resistant additives into XLPE insulation material,and improve its water tree retardant properties. The other is to design a new powercable structure to prevent the incursion of moisture into the XLPE insulation.However, there is no complete set of experimental system or testing standard for therapid detection of water tree retardant cross-linked polyethylene (WTR-XLPE) powercables.Samples used here is XLPE and WTR-XLPE insulation sheet with1±0.1mm inthickness and25mm in diameter. And they were aged in1.0N NaCl conductivesolution and under10kV test voltage for120and240hours. After water treeing test,all the samples were tested by broadband dielectric spectroscopy, differential scanningcalorimetry, Fourier transform infrared spectroscopy, as well as power frequencyvoltage withstand test. By analyzing the results, an experimental system of rapiddetection for WTR-XLPE power cables is obtained. The operation of this testingmethod is as follows:1. Use the broadband dielectric spectrometer to test the dielectric loss-temperature spectrum of the insulation with condition of0.1Hz and temperature changing from45℃to70℃. Test the dielectric loss-frequency spectrum at roomtemperature and under frequency changing from0.1Hz to10Hz. The dielectric loss ofWTR-XLPE insulation shows a rapid increase with the increasing of testingtemperature and aging time.2. Repeatedly test the Oxidation Induction Time (OIT) of the insulation withsame weight by the DSC: the OIT of WTR-XLPE insulation is influenced less bywater tree aging degree.3. AC withstand voltage test the breakdown voltage of the insulations underworking frequency, and the pressure resistance duration. The drop level of these twoparameters of WTR-XLPE insulation is smaller than XLPE insulation.