Study on electrical tree growth characteristics of XLPE nanocomposites for medium voltage cable insulation applications

Abstract

Underground cables are mostly preferred in power distribution network where it is difficult to use the overhead lines particularly in densely populated cities. Electrical Treeing is one of the major causes of degradation and failure of polymeric insulation material in the underground cables. Crosslinked polyethylene (XLPE) is the mostly used insulating material for underground (UG) cables. A major concern for AC cable reliability is electrical failure due to Partial Discharges (PD) and electrical tree growth. In recent times, nano-composites are evolving as promising dielectric materials particularly for MV UG cable applications. Nanocomposites are the new type of materials found with the support of nanotechnology. In the case of nanocomposites, base material such as polyethylene, epoxy or XLPE is incorporated with some amount of nano filler materials in order to improve its electrical and thermal properties. Some researchers also studied the effects of nanoparticles including SiO2, Al2O3, NB, ZnO, etc. in the base polymeric materials on the growth of electrical tree. CIGRE working group D1.24 has reported comprehensive experimental results of XLPE/SiO2nanocomposites and confirmed noticeable improvements in dielectric characteristics over unfilled XLPE even at low volume concentration of nanofillers. Severity of insulation failure due to electrical treeing can be predicted through PD monitoring techniques. Some researchers also analyzed the treeing process and time-frequency characteristics of PD pulses in HV XLPE cable and reported the existence of good correlation between PD erosion, PD resistance and tree initiation time newline