Coupling Effect of Molecular Chain Displacement and Carrier Trap Characteristics on DC Breakdown of HDPE/LDPE Blend Insulation

Abstract

This work focuses on the coupling effect of molecular chain displacement and trap characteristics on direct current (DC) breakdown properties of high density/low density polyethylene (HDPE/LDPE) blend insulation. Frequency domain spectroscopy (FDS) and isothermal discharge current (IDC) are used to characterize the dielectric relaxation and trap characteristics of HDPE/LDPE blends. A DC breakdown model is proposed to reveal the mechanisms of the molecular chain displacement and carrier trap on the DC breakdown strength. The dielectric relaxation α and δ present segmental motions and thermal ion polarization behaviours of HDPE/LDPE blends, respectively. α dielectric relaxation strength (Δεα) increases as the amount of HDPE increases from 0 to 5 wt%, and then declines with a further increase of HDPE content to 20 wt%. According to the velocity equation, the increase of Δεα will increase the molecular chain displacement, resulting in a larger free volume, which will provide electrons with larger free path λ to form hot electrons. A positive correlation exists between the activation energy of the dielectric relaxation process δ and trap density, and the increase of δ dielectric relaxation strength (Δεδ) will adversely affect the breakdown strength of the specimen. HDPE/LDPE blends with 15 wt% HDPE content have lower Δεα and lowest Δεδ, which decreases the mean free path λ of molecular chain and thermal ion polarization. At the same time, it has the highest deep trap density, thus increasing the probability of hot electrons being captured and improving the DC breakdown strength. It is concluded the breakdown of the dielectric is synergistically affected by the molecular chain displacement and carrier trap.

Phase Equilibria and Interdiffusion in Bimodal High-Density Polyethylene (HDPE) and Linear Low-Density Polyethylene (LLDPE) Based Compositions

“…Thus, by extrusion mixing, it is possible to obtain a multimodal PE, which combines several polymers with different molecular weights, different degrees of branching and density. The importance of this area of research is confirmed by unrelenting attention to mixed compositions based on polyolefins and, in particular, polyethylene [ 3 , 4 , 5 , 6 ].…”

Modified Molecular Chain Displacement Analysis Employing Electro-Mechanical Threshold Energy Condition for Direct Current Breakdown of Low-Density Polyethylene

“…The coefficients used in the BCT model were obtained from previous experimental studies, such as electron and hole mobility, deep trap energy and density, and injection barrier height that varies with temperature [ 24 , 25 , 26 , 27 ]. In particular, we assumed that deep trap energy has a single level for simplicity in this numerical analysis model.…”

“…With space charge analysis development, studies measuring the breakdown strength and analyzing the mechanisms have been conducted as the critical factor for stability and reliability. The breakdown strengths of polymeric insulators have been studied using numerical and statistical experimental approaches [ 24 , 25 , 26 , 27 ]. There are several models to interpret the breakdown mechanisms inside the polymeric insulators, such as the electro-mechanical model, electron avalanche model, molecular chain displacement model, and phase-field model [ 1 , 27 , 28 ].…”

Thermally stimulated depolarization current spectra of cross‐linked polyethylene and the influence of cross‐linking byproducts

“…In addition, there is a relation between chain segment motion and space charge buildup where less restricted chain motion allows for more charging. [ 30 ] These factors explain both the differences between individual samples and between sample types, as LDPE would be less restricted in chain motion than XLPE and differences in the degassing temperature would also lead to different results.…”

“…Instead, net homocurrent arises from a combination of interface states and charge injection, which differences being due to factors such as restricted chain motion in XLPE preventing chain scission and void formation that promotes space charge buildup. [ 30 ] This restriction originates from the greater cross‐link density in XLPE, which reduces the motion of charged chain fragments that move due to the applied heat and electrical field. There was no meaningful difference in the obtained activation energies on average between the two types of samples, however, degassing temperature appeared to influence how far charges were able to migrate through the sample during poling for XLPE by altering these interface states, which influenced the resulting discharge current.…”