Finite Element Analysis of the Breakdown Prediction for LDPE Stressed by Various Ramp Rates of DC Voltage Based on Molecular Displacement Model

Abstract

Predicting the electrical breakdown of polymers is critical for certifying the endurance and lifetime of high voltage power equipment. Since various factors contribute nonlinearly to the breakdown phenomena of polymer insulators, it is difficult to assess the impact of each factor independently. In this study, we numerically analyzed the breakdown phenomenon because of the ramp rate of the DC voltage applied to a polymer insulator, low-density polyethylene (LDPE), using the finite element method (FEM). To predict the breakdown initiation, we analyzed the relaxation time of the conduction current through the insulator as a significant indicator. The bipolar charge transport (BCT) model was used to analyze the charge behavior within the LDPE, and the breakdown voltage was predicted by incorporating the molecular displacement model. This analysis was conducted for a wide range of ramp rates from 10 to 1500 V/s. The current density was calculated using two different methods, namely the energy and average methods, and the results were compared with each other. The results of the numerical model were further verified by comparing with those from experiments reported in the literature.

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

“…The decrease in breakdown strength can be explained as the accumulated hetero-charge intensifies the local electric field distortion as T 0 increases. Moreover, these results agree well that the breakdown strength increases with the voltage ramp rate analyzed in our previous research results [ 40 ].…”

“…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.…”

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

“…14. The Pearson correlation and Sobol sensitivity index were used to analyze 168 cases, including our previous research [24]. Thickness, temperature, and charge injection barrier height were found to have a negative correlation with breakdown strength, while a voltage ramp rate was found to be positively correlated with breakdown strength.…”

“…This model was used to determine the initiation of breakdown phenomena and breakdown strength. [24].…”

“…The initiation of the breakdown phenomenon is determined by sever molecular chain displacement, as expressed in (12). In our preceding study, the mechanical stress caused by molecular chain displacement was explained using a physical approach in terms of the momentum-impact relation [24]. For a given same magnitude of electric force, the amount of impact stored in a molecular chain will vary with the time at which the electric force acts.…”