Investigation On Space Charge Behavior Of PE/MMT Nanocomposites

Plastic is displacing oilpaper and becoming the main insulation materials of high voltage direct current cable because of its unique advantages. When the plastic insulated cable like polyethylene(PE) and crosslinked polyethylene(XLPE) work, space charge is easily accumulated in the insulation materials. It will cause the distortion of partial electric field and even cause aging and breakdown of the insulation. In order to inhibit space charge accumulation and improve the dielectric properties, people have started to add nano particle into polymer.Low density polyethylene/montmorillonte nanocomposites(LDPE/O-MMT) were prepared by melting intercalation while low density polyethylene(LDPE) was used as basis material and organic montmorillonite(O-MMT) was served as modifier. Crosslinked polyethylene/montmorillonite nanocomposites(XLPE/O-MMT) were prepared by peroxide crosslinking method. Space charge distribution of composites was measured by Pulsed Electro-Acoustic(PEA) method when the samples was under electric field and in short-circuit conditions, and the effects of O-MMT content on space charge distribution were also researched. Thermally stimulated current(TSC) spectra of composites was obtained, and volume resistivity at room temperature was measured. The influence of trap density, trap depth and carrier mobility on space charge behavior were also discussed in this paper.The test results of PEA method show that when the samples are under 50kV/mm DC electric field, the homocharge accumulate in the LDPE sample and the heterocharge accumulate in the XLPE sample. Compared with LDPE, XLPE has stronger ability to inhibit space charge accumulation. The space charge density of composites decreases first and then increases with the increasing of O-MMT content, and it become the least value both in LDPE/O-MMT composites with 0.5% concentration of O-MMT and in XLPE/O-MMT composites with 1% concentration of O-MMT. The TSC test results illustrate that the trap density and depth of XLPE/O-MMT composites increase with the increasing of O-MMT content, but they come to the least value in the sample with 1% concentration of O-MMT. The test results of volume resistivity indicate that the conductivity of composites also decreases first and then increases with the increasing of O-MMT content.