基于光纤应变和温度分布的海底电缆机械与电气特性分析及故障诊断方法

Submarine power cables are widely used in many important fields such as power supply for islands and offshore oil platform, offshore wind power transmission, et.al. It is necessary to monitor the running condition of submarine power cables. Distributed strain and temperature measurement of optical fiber is a new technology and method to monitor the running condition. There is a urgently problem that how to analyze the mechanical and electrical characteristics of submarine power cables and diagnose the faults through strain and temperature distribution of optical fiber. In this project, the mechanical and electrical mathematical model of submarine power cables will be established. The experiments in laboratory and field will be carried out. The general relation functions, between stress or strain of structures in the cables and strain of the fiber, will be established. The stress or strain distribution of the cables will be calculated from strain of the fiber using above functions. The mechanical characteristic change of the cables will be analyzed according to distribution characteristic and change tendency of stress and strain in transportation, laying and operation. Meanwhile, the general relation functions between temperatures of conductor, metal sheath and optical fiber will also be established. The temperature distribution of conductor and metal sheath will be calculated from temperature of the fiber using above functions. The electrical characteristic change of the cables will be analyzed according to distribution characteristic and change tendency of temperature in cyclic load, short-time overload and long-time running. Finally, the distribution and variation principle in strain and temperature of the cables will be extracted, and the mechanical and electrical faults will be diagnosed such as anchor hit, hitch, abrasion, interphase short circuit, grounded short circuit, broken circuit and electric leakage. The completion of the project will provide new method and theoretical basis for health condition monitoring of submarine power cables.

海底电缆普遍用于岛屿和海上石油平台供电、海上风电场输电等场合，其状态监测十分重要，分布式光纤应变和温度测量技术为此提供了新的手段。如何通过光纤的应变和温度分布揭示海底电缆的机械和电气特性并进行故障诊断成为亟待解决的问题。本项目通过海底电缆机械和电气数学模型构建、实验室试验、现场试验等手段，建立其内部各层结构应力或应变与光纤应变的通用关系函数，利用光纤的应变分布计算海底电缆本体的应力或应变分布，分析其在运输、敷设、运行等过程中的机械特性变化；建立海底电缆导体和金属护套温度与光纤温度的通用关系函数，利用光纤的温度分布计算海底电缆导体和金属护套的温度分布，分析其在周期负荷、短时过负荷、长期运行等情况下的电气特性变化；提取锚砸、钩挂、磨损、相间短路、接地短路、断路、漏电等故障发生时海底电缆的应变温度分布和变化规律，进行机械和电气故障诊断。项目的完成可为海底电缆健康状态监测提供新的方法和理论依据。

海底电缆普遍用于岛屿和海上石油平台供电、海上风电场输电等场合，其状态监测十分重要，分布式光纤应变和温度测量技术为此提供了新的手段。如何通过光纤的应变和温度分布揭示海底电缆的机械和电气特性并进行故障诊断成为亟待解决的问题。本项目对海底电缆直线拉伸、卷绕和张力弯曲等常见机械试验进行了理论分析，构建了直线拉伸、弯曲和扭转的有限元模型，进行了实体试验，建立了海底电缆应力与光纤应变的关系方程；构建了海底电缆稳态、周期和短时过负荷热力学有限元模型，建立了海底电缆和光纤的温度关系；提出了利用传感光纤应变和温度计算海底电缆应变和温度的方法，为缆体应变和温度信息的获取提供了理论支持。建立了锚砸和钩挂的动力学有限元模型及接地短路和漏电的有限元电热耦合模型，提取了故障发生后的应变和温度分布数据，得出了不同故障时应变和温度的空间分布与时间变化特征，克服了实体试验实施难度大、数据提取困难的难题，为故障检测和诊断提供了有效的数据支持。提出了基于分布式光纤应变和温度分布的海底电缆故障检测和诊断方法。利用归一化方法消除了系统噪声和环境温度对故障检测的影响，结合超阈值数据点个数和连续超阈值次数进行故障检测和报警，降低了误报率；利用二阶八尺度coif小波对奇异点敏感的特点准确发现故障位置，利用时频多分辨特点准确判断故障类型，为工程应用提供了有效可行的方法。