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

Minhee Kim,Se-Hee Lee

doi:10.3390/polym13162746

Abstract

In an HVDC environment, space charge accumulated in polymeric insulators causes severe electric field distortion and degradation of breakdown strength. To analyze the breakdown characteristics, here, the space charge distribution was numerically evaluated using the bipolar charge transport (BCT) model, considering the temperature gradient inside the polymeric insulator. In particular, we proposed an electro-mechanical threshold energy condition, resulting in the modified molecular chain displacement model. The temperature gradient accelerates to reduce the breakdown strength with the polarity-reversal voltage, except during the harshest condition, when the temperature of the entire polymeric insulator was 70 °C. The energy imbalance inside the insulator caused by polarity-reversal voltage reduced the breakdown strength by 82%. Finally, this numerical analysis model can be used universally to predict the breakdown strength of polymeric insulators in various environments, and help in evaluating the electrical performance of polymeric insulators.

Highlights

Increasing demand for eco-friendly energy has led to the development of HVDC cables for low Joule loss in power transmission
The study of space charge measurement has been conducted for several decades with various methods, such as pulsed electro-acoustic (PEA), pressure wave propagation (PWP), laser induced pressure pulse (LIPP), and current integration (Q(t)) methods, etc. [14,15,16,17,18,19,20]
In recent studies on numerical breakdown strength prediction employing various models, the space charge effect was not considered in some limits, or only the special cases were dealt with related to the applied voltage and temperature

Summary

Introduction

Increasing demand for eco-friendly energy has led to the development of HVDC cables for low Joule loss in power transmission. In an HVDC environment, many space charges are accumulated inside the polymeric insulator due to continuously applied one-directional voltage [6,7,8,9] This space charge causes a distorted electric field, which plays a critical role in lifetime reduction [10,11,12,13]. In recent studies on numerical breakdown strength prediction employing various models, the space charge effect was not considered in some limits, or only the special cases were dealt with related to the applied voltage and temperature. High DC voltage causes a severe temperature gradient inside to change the space charge distribution These accumulated space charge behaviors greatly affect the breakdown strength of the systems. Encouraged by the recent research, here, we analyzed the breakdown phenomena of low-density polyethylene (LDPE) under PRV with a temperature gradient For this purpose, we adopted the BCT model for analyzing space charge.

Analysis Setup and Test Conditions

Bipolar Charge Transport Model

Findings

Conclusions