A Study On Dielectric Property And Space Charge Behavior Of Low Density Polyethylene With Montmorillonite As Filler

Polyethylene (PE) is widely used in various power cables as insulation materialbecause of its excellent electrical and mechanical properties. For long-term operation,insulation aging caused by electric tree has a great impact on lifetime of polyethylene,which is also major caurse for insulation damage and equipment failure. In order to finda solution to overcome this drawback, this paper puts forward a compounding methodto improve properties of PE materials by adding montmorillonite (MMT) into the lowdensity polyethylene (LDPE) matrix. In order to explore the possible way of furtherlyimproving PE materials’ properties, a pre-treatment of applying AC electric field wasperformed. Several measurements were carried out to evaluate basic properties of thematerial, especially, dielectric performance and space charge characteristics of themodified LDPE materials. The main research results are listed as follows:①By using melting blending method, organically modified MMT was addedinto LDPE to prepare MLDPE sample, and AC electric field was applied to MLDPE toprepare EMLDPE sample with a self-devised model. Results of relevant measurementsreveal that: the enlarged interlayer distance of MMT suggestes a successful intercalationcompounding of LDPE and MMT; the dispersion of MMT in LDPE is considerablelyeven and uniformed; with the additive of MMT, the material has a better thermalstability and higher breakdown strength; the AC electric field pretreatment has a slightimpact on thermal stability and breakdown strength of the materials.②After adding MMT into LDPE matrix: for MLDPE materials with1%of MMT,the relative permittivity greatly reduced compared with unmodified LDPE, but withincreased content of MMT in MLDPE, the relative permittivity increases; with theapplication of MMT, dielectric loss factor of the material increases slightly, and itincreases with higher content of MMT in MLDPE;③After AC electric field pre-treatment, EMLDPE material gains a small increasein relative permittivity, and the higher the applied electric field intensity is,the biggervalue of material’ relative permittivity is; the dielectric loss spectrum of the materialswitched towards high frequency direction after AC electric field pre-treatment, morespcsifically, the dielectric loss of EMLDPE material decreases in low and highfrequence region and increases in middium frenquence region.④The results of space charge measurement of the material show that: The application of MMT in LDPE helps restrain the accumulation of space charge inside thematerial, but its restraining effect declines with insceased content of MMT in LDPE;⑤The results of space charge measurement of the material show that: The ACelectric field pretreatment also helps restrain the accumulation of space charge insidethe material, and its restraining effect also declines with insceased content of MMT inLDPE; at the same time, after AC electric fields pre-treatment, the decay rate of spacecharge inside the material decreases.