Numerical Prediction of DC Breakdown Characteristics in LDPE With Current Profile as Critical Index

Abstract

Understanding the DC breakdown characteristics of polymeric insulators is essential for stable operation of high-capacity DC electrical equipment. To predict the breakdown characteristics of lowdensity polyethylene (LDPE), we propose a numerical methodology with a new critical index in which the internal current varying with temperature, thickness, and injection barrier height. To evaluate this currentbased index, we applied the fully coupled bipolar charge transport (BCT) and molecular chain displacement (MCD) models to analyze the influence of each variable on breakdown phenomena. The results of this analysis revealed that the amount of space charge accumulation within the insulator has a maximum value at approximately 50 ℃, which corresponds to the known morphological transition temperature of LDPE. The breakdown strength calculated using this numerical model was found to decrease with increasing temperature and thickness. Although injection barrier height at the electrode was found to be negatively correlated with breakdown strength, its effect was not as significant as that of the other variables. The breakdown strength values obtained using this numerical method were found to be in close agreement with values reported in the literature. Based on these results, we newly suggest the physical quantity to predict the breakdown strength, the current relaxation speed, which is the slope of the Boltzmann sigmoid function, as a positively correlated index. Finally, we determined that the breakdown phenomena are initiated when the amount of impact accumulated in the insulator changes discontinuously and analyzed the contribution of factors affecting the breakdown using the Pearson correlation coefficient and the Sobol sensitivity index.

Refining the physical description of charge trapping and detrapping in a transport model for dielectrics using an optimization algorithm

“…5 × 10 −14 vs 1.5 × 10 −13 at 20°C and 40 kV/mm). These results on mobility values are consistent with literature reports (Le Roy et al , 2004; Thomas et al , 2011; Hoang et al , 2016; Kim et al , 2020), where both vary in the same range [10 −14 , 10 −12 m 2 /Vs].…”

“…5 Â 10 À14 vs 1.5 Â 10 À13 at 20°C and 40 kV/mm). These results on mobility values are consistent with literature reports (Le Roy et al, 2004;Thomas et al, 2011;Hoang et al, 2016;Kim et al, 2020), where both vary in the same range [10 À14 , 10 À12 m 2 /Vs]. The estimated values of the average intertrap distance between two shallow traps are of the order of nm, consistently with the values reported in the literature (Chen and Zhao, 2011;Chen et al, 2016;Dennison and Brunson, 2008;Ziari et al, 2010;Nath et al, 1990;Kim et al, Figure 5.…”

“…This description of hole transport shows the complexity of describing accurately the physical phenomena and hence of getting precise constants or parameters related to the polymer physics. The intertrap distances are an example of this kind of complexity, with reported values ranging from a = 2.8 to 10 nm (Lewis and Llewellyn, 2013; Chen et al , 2016; Dennison and Brunson, 2008; Ziari et al , 2010; Nath et al , 1990; Kim et al , 2020). This complexity is addressed in this study by optimizing the intertrap distance parameter, considering the asymmetry between electrons and holes.…”

“…In the literature, most of the presented BCT models consider the trapping and detrapping rates independent of the electric field (Le Roy et al , 2004; Hallak et al , 2020; Thomas et al , 2011; Hallak et al , 2021; Hoang et al , 2016). Nevertheless, some works have addressed experimentally and theoretically the relationship between trapping and detrapping phenomena and the electric field (Kim et al , 2020; Doedens et al , 2020). As regards the temperature dependency of the detrapping rate, it is described by a thermally activated process.…”

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

“…The breakdown strength was calculated by using the M-MCD model as depicted in Figure 8 and Figure 9 . These numerical analysis results were verified through the experiments in the previous study [ 39 , 40 , 41 ] (detailed results to verify the numerical analysis model are included in the Supplementary Material, S2-3 ). Figure 8 a shows the calculated breakdown strength under a constant voltage with constant temperature, CV@CT, and a polarity-reversal voltage with constant temperature, PRV@CT.…”