基于光纤布里渊散射技术的海底电缆在线监测及故障点定位方法研究

Daily inspection and fault location of the submarine cable is very difficult because it is long length, high cost and lying under the ocean. At present, there have not any effective on-line monitoring and fault location method for the submarine cable. On the basis of the systematic investigation on the structure and physical properties of submarine cable, a condition monitoring system based on Brillouin scattering with its residual fiber is designed and constructed in this project. In the system, a wide spectrum laser with multiple longitudinal modes is adopted. Every individual longitudinal mode in the fiber excites Rayleigh and Brillouin scattering signals, the self heterodyne of which will result in Brillouin frequency-shift signals. And the SNR (Signal-to-Noise Ratio) will be improved through the superposition of these signals. Based on it, simultaneous measurement of temperature and strain can be achieved. According to geometry and material properties of typical submarine cables, the coupled models, including electricity, heat and mechanics, will be formulated in the commercial finite element software. Based on solving these models, the relationship among its conditions, temperature and strain of the fiber, frequency shift and intensity of Brillouin scattering spectrum is built, which can reveal the influences of insulation deterioration, grounding to earth, hitting by anchor and break of submarine cable on temperature and strain of submarine cable and fiber. The results can provide scientific basis on electrical and mechanical condition monitoring and fault diagnosis for submarine cable. On the basis, the route information is extract from the measured data in submarine cable monitoring system, which is fused with the submarine topography, geological structure of seafloor, construction details, and the submarine cable fault can be located accurately.

海底电缆距离长、造价高，铺设在海底导致日常巡检和故障检测困难，目前尚无有效的在线监测和故障定位方法。本项目拟在深入研究海底电缆结构和物理特性的基础上，利用备用纤芯设计并构建基于光纤布里渊散射技术的海底电缆状态监测系统。该系统采用多纵模宽谱激光器，利用各独立纵模在光纤中产生的瑞利和布里渊散射自外差得到的布里渊频移单频信号叠加，显著提高信噪比，实现温度和应变的同时有效测量。根据典型海底电缆的结构和材料参数，利用有限元软件构建海底电缆的电、热和机械耦合模型，建立海底电缆运行状态参数、光纤的温度和应变、布里渊频移和强度三者的数学关系模型，揭示海底电缆绝缘劣化、接地、锚砸、钩挂等运行故障发生时海底电缆与光纤温度和应变的分布规律，为海底电缆电气和机械的状态监测和故障诊断提供科学依据。在此基础上提取在线监测系统测量曲线的路由特征，与海底地形、地质结构和施工细节进行数据融合，实现海底电缆故障准确定位。

海底电缆距离长、造价高，铺设在海底导致日常巡检和故障检测困难，目前尚无有效的在线监测和故障定位方法。本项目在深入研究海缆结构和物理特性的基础上，利用备用纤芯提出并构建了基于光纤布里渊散射技术的海缆状态监测系统。（1）本项目解决了通过同一光纤中瑞利与布里渊自外差实现布里渊强度和频移检测的理论计算问题，实现了多模激光器光谱特性及外差检测的数学描述，解决了系统建模及信噪比分析计算和改善的问题。搭建了基于多纵模激光器间接调制、本地外差检测的布里渊光时域反射系统，推导了本地外差检测系统信噪比的数学表达式；（2）针对光纤布里渊分布式传感系统频谱提出了布里渊散射谱特征快速、高精度提取方法，基于最小二乘拟合算法建立了基于洛伦兹模型、高斯模型、伪Voigt模型和Voigt模型的布里渊增益谱拟合的目标函数，实现了基于洛伦兹模型、高斯模型、伪Voigt模型和Voigt模型的布里渊增益谱的拟合算法。（3）根据光纤复合海底电缆的现场情况建立了模拟光路，进行了温度和应变测量实验，实现了已敷设传感光纤整条光路上的温度和应变区分测量，为工程应用提供了理论和实验依据。（4）基于有限元理论、热力学和结构动力学理论构建了模拟海缆典型电气和机械故障情况的有限元建模方法，并对模型的可靠性进行了一定程度的验证，为海缆故障状态下的建模仿真提供了思路。（5）通过布里渊分布式光纤应变/温度测量数据与实际海底电缆状态信息融合，提取海缆路由特征信息，实现了海底电缆故障点检测和准确定位。