DC Breakdown Modulated by Molecular Chains Movements and Trap Characteristics of HDPE/LDPE Blend Insulation

Abstract

Polyethylene (PE) is an environmentally friendly material, and is generally used as cable insulation materials. This paper mainly researches the coupling effect of dielectric polarization behaviors and traps level characteristics on direct current (DC) electrical breakdown performance of five high density/low density polyethylene (HDPE/LDPE) blends specimens. HDPE/LDPE specimens are prepared by high temperature blending and hot-press forming methods. Broadband dielectric spectroscopy (BDS) and isothermal decay current (IDC) measurements are employed to reveal the dielectric polarization behaviors and traps level characteristics of five HDPE/LDPE specimens. A novel molecular chains movement model is employed to investigate the mechanism of the molecular chains movements in the HDPE/LDPE dielectrics. The breakdown field strength of five HDPE/LDPE specimens reaches maximum when the HDPE content increases to 15 wt%, and then decreases with a further addition of HDPE to 20 wt%. The dielectric relaxation polarization a is attributed to molecular chains movements in HDPE/LDPE blends, and a behavior intensity (Δ ε <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α</inf> ) increases with the HDPE content from 0 to 5 wt%, and then reduces with a further addition of HDPE content to 20 wt%. The molecular chains movements will be strengthened on account of the increase of (Δ ε <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α</inf> ), which provides charges with larger mean free volume to form high energy electrons. The increased traps density raises the possibilities of high energy electrons being captured, and enhance the breakdown performance of the specimen. It is deduced that the DC breakdown properties of HDPE/LDPE blends are influenced by molecular chains movements as well as traps characteristics.