基于模拟电荷法的10 kV XLPE电缆附近电场计算

论文总字数：22905字

摘 要

随着近几年来直流输电的快速发展，对输电电缆的要求逐渐提高，传统的油浸式和充油式绝缘电缆不再适用，交联聚乙烯(XLPE)电缆由于具有良好的电气性能和自身安装维护简单等优势逐步取代以往电缆成为主流，广泛的应用于城市输电缆电、跨越海峡输电、穿越隧道送电和可再生能源发电等各个方面。XLPE电缆绝缘老化一直严重威胁着供电的安全性和可靠性。电缆绝缘老化一般是由于内部存在缺陷发生局部放电，缺陷在电场的长期作用下不断延伸发展，最终导致电缆绝缘层被击穿，引起短路接地故障。因此研究电缆内部缺陷周围的电场分布在电缆缺陷检测方面有较强的理论意义和应用价值。

本文选择了模拟电荷法作为电缆内部电场计算方法。由于电缆的物理几何结构有轴对称特性，因此以模拟电荷法中的环形电荷代替有限元中的单个元能够大幅降低数值计算量并提高计算效率。本文对正常电缆和缺陷电缆的不同情况进行仿真分析比较。当电缆正常时，电缆的最大场强出现在电缆绝缘层内表面，电场强度沿电缆半径方向逐步降低，屏蔽层以及外部场强都为0；当电缆出现水树缺陷或者导电缺陷时，缺陷周围的场强发生畸变，畸变程度与缺陷的位置和尺寸有关：当缺陷越靠近电缆铁芯（电缆高压端）时，畸变越严重；缺陷尺寸越大时，电缆畸变率越高。导电缺陷附近的电位和场强都会产生很明显的改变，容易成为水树发展的起始点。

本文主要研究了电缆绝缘层正常和出现缺陷时电场的分布，表明了电缆出现缺陷会使电缆绝缘层电场畸变，并且随着缺陷在电场的影响下延伸发展会导致电场畸变越来越严重，破坏绝缘层的电气性能，造成电缆击穿等重大事故。本文的研究成果为通过电场测量来检测电缆内部缺陷的实践应用提供了理论依据，为保障电缆供电的安全性和可靠性做出了一定的贡献。

关键字：模拟电荷法，电缆，电场，水树缺陷，导电缺陷

ABSTRACT

With the rapid development of dc power transmission in recent years, the transmission cable requirements gradually improve, the traditional oil-immersed and oil filled cable is no longer applicable, crosslinked polyethylene (described.properties) cable with good electric performance and its simple installation and maintenance advantages gradually replace the previous cable into the mainstream, widely used in urban transmission cable sending electricity, across the channel transmission, through the tunnel and many aspects, such as renewable energy power generation. XLPE cable insulation aging has been a serious threat to the safety and reliability of power supply. The aging of cable insulation is generally due to the partial discharge of internal defects, which continue to develop under the long-term action of electric field, eventually leading to the breakdown of cable insulation layer and causing short-circuit grounding fault. Therefore, it is of great theoretical significance and application value to study the electric field distribution around the cable internal defects.

In this paper, the analog charge method is chosen to calculate the electric field inside the cable. Because of the axisymmetric characteristics of the physical and geometric structure of the cable, replacing the single element in the finite element with the annular charge in the analog charge method can greatly reduce the amount of numerical calculation and improve the calculation efficiency. This paper analyzes and compares the different conditions of normal cable and defective cable. When the cable is normal, the maximum field intensity of the cable appears on the inner surface of the cable insulation layer, and the electric field intensity gradually decreases along the radius of the cable, and the shielding layer and the external field intensity are all 0. When the water tree defect or conductive defect occurs in the cable, the field intensity around the defect will be distorted, and the degree of distortion is related to the location and size of the defect. The larger the defect size, the higher the cable distortion rate. The electric potential and field intensity near the electrical conductivity defect will change obviously and easily become the starting point of water tree development.

This paper mainly studies the distribution of electric field when the cable insulation layer is normal and defects occur, showing that the electric field distortion of the cable insulation layer will be caused by the cable defects, and the electric field distortion will be more and more serious as the defects are extended and developed under the influence of electric field, which will damage the electrical properties of the insulation layer and cause major accidents such as cable breakdown. The research results of this paper provide a theoretical basis for the practical application of electric field measurement to detect the internal defects of cables and make a certain contribution to the security and reliability of cable power supply.

KEY WORDS: analog charge method, cable, electric field, water tree defect, conductive defect.

目录

摘要

ABSTRACT

第一章 绪论 1

1.1引言 1

1.2 交联聚乙烯（XLPE）电缆 1

1.3电缆故障及产生原因 2

1.4研究目的 3

第二章 实验原理 4

2.1模拟电荷法概念以及应用 4

2.2二维场中的模拟电荷 5

2.3轴对称场中的模拟电荷 6

2.3.1点电荷 6

2.3.2线电荷 7

2.3.3环形电荷 9

2.4多种介质中电场边界条件 10

2.5电缆的老化和击穿 11

2.5.1固体电介质的击穿 11

2.5.2固体电介质的老化 11

2.6本章小结 14

第三章 模型建立与仿真结果 15

3.1电缆模型建立 15

3.2电缆水树缺陷 17

3.2.1水树位置不同 17

3.2.2水树尺寸不同 21

3.3电缆导电缺陷 24

3.3.1导电缺陷位置不同 24

3.3.2缺陷尺寸不同 28

3.4本章小结 30

第四章 结论与展望 31

4.1结论 31

4.2未来展望 31

参考文献 32

致 谢 33

1. 绪论

1.1引言

近几年来，随着电力电子技术的不断进步和发展，高压直流输电技术也随之成长起来，有了投入到实际应用的条件和基础，加上具有着比高压交流输电明显的容量大、成本低、适合长距离输电的优势，高压直流输电占据输电份额提高，与此同时，对电缆的要求也随之严格。这个时候传统的充油式绝缘电缆和油浸式纸绝缘电缆难以承载很大的容量或者不适合长距离输电等原因满足不了要求。而交联聚乙烯（XLPE）电缆由于自身安装维护简单，电气性能良好等特点，逐步取代了以往的油浸式绝缘电缆和充油式电缆成为了主流，应用于跨越海峡输电、穿越隧道送电和可再生能源发电等方面。

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