Purpose

In high-voltage direct current (HVDC) cable systems, space charges accumulate because of the constant applied voltage and the nonlinear electric conductivity of the insulating material. The change in the charge distribution results in a slowly time-varying electric field. Space charges accumulate within the insulation bulk and at interfaces. With an operation time of several years of HVDC systems, typically the stationary electric field is of interest. The purpose of this study is to investigate the influence of interfaces on the stationary electric field stress and space charge density.

Design/methodology/approach

An analytic description of the stationary electric field inside cable insulation is developed and numerical simulations of a cable joint geometry are applied, considering spatial variations of the conductivity in the vicinity of the electrodes and interfaces.

Findings

With increasing conductivity values toward the electrodes, the resulting field stress decreases, whereas a decreasing conductivity results in an increasing electric field. The increased electric field may cause partial discharge, resulting in accelerated aging of the insulation material. Thus, interfaces and surfaces are characterized as critical areas for the reliability of HVDC cable systems.

Research limitations/implications

This study is restricted to stationary electric field and temperature distributions. The electric field variations during a polarity reversal or a time-varying temperature may result in an increased electric conductivity and electric field at interfaces and surfaces.

Originality/value

An analytical description of the electric field, considering surface effects, is developed. The used conductivity model is applicable for cable and cable-joint insulations, where homo- and hetero-charge effects are simulated. These simulations compare well against measurements.

中文翻译：

---

对高压电缆系统的界面和表面处的电场建模

目的

在高压直流（HVDC）电缆系统中，由于恒定的施加电压和绝缘材料的非线性导电性，空间电荷会积累。电荷分布的变化导致缓慢的时变电场。空间电荷在绝缘体内部和界面处累积。在HVDC系统的运行时间为数年的情况下，通常需要关注固定电场。这项研究的目的是研究界面对固定电场应力和空间电荷密度的影响。

设计/方法/方法

考虑到电极和界面附近电导率的空间变化，开发了电缆绝缘层内部固定电场的解析描述，并应用了电缆接头几何形状的数值模拟。

发现

随着朝向电极的电导率值的增加，所产生的场应力减小，而电导率的减小导致电场的增大。增大的电场可能会导致局部放电，从而导致绝缘材料加速老化。因此，接口和表面被表征为HVDC电缆系统可靠性的关键区域。

研究局限/意义

本研究仅限于固定电场和温度分布。极性反转或随时间变化的温度期间的电场变化可能导致界面和表面处的电导率和电场增加。

创意/价值

考虑到表面效应，提出了对电场的分析描述。使用的电导率模型适用于电缆和电缆接头绝缘，其中模拟了均电荷和杂电荷效应。这些模拟与测量结果比较良好。