Research On Condition Monitoring Of Optical Fiber Composite Submarine Power Cable Based On Distributed Strain And Temperature Sensing Technology Using Optical Fiber

Submarine power cable is an important link to ensure the power supply of islands and offshore oil platform and power transmission of offshore wind power supply. There is important significance for safeguarding social and economic development by obtaining the real-time running condition of submarine power cable and ensuring the safe and stable operation. Contrapose the problem of special laying environment and difficulty in obtaining the running condition, the condition monitoring method using distributed optical fiber strain and temperature sensing technology is proposed. The parameters configuration method in the monitoring system and the engineering method for strain and temperature distinguishment were studied. The method to establish the strain and temperature relation between submarine power cable and optical fiber was also studied. The methods for extracting features of mechanical and electrical faulses, detecting and diagnosing the faults were studied too. All above work is used to provide theoretical and technical support for condition monitoring of submarine power cable. The main research achievements are presented as follows:1. The parameters configuration method in the monitoring system was proposed contrapose the measurement accuracy and real time. The relation equation between measurement accuracy & real-time and system parameters were established. The key points positioning method, superior to traditional OTDR, was proposed which can position the connections and feature points along the sensing optical path using Brillouin shift measured by BOTDR. Finnally, a new method to simultaneously calibrate the coefficients of Brillouin shift to strain and temperature was proposed using linear thermal expansion characteristics of metal pipe.2. The initial Brillouin power distribution along the laid optical fiber was obtained using heuristic method. The measurement error caused by multiplicative noises in sensing system was conquered by normalization. The spikes in the Brillouin spectrum peak power profiles at positions of changed temperature or strain were eliminated using spectrum width change. According to the above work, the distinguishing measurement of optical fiber strain and temperature was realized using Brillouin shift and spectrum peak power measured by BOTDR. In addition, the characteristics of only sensitive to temperature was used to compensate the Brillouin shift’s cross sensitive to strain and temperature with ROTDR for single-mode optical fiber. The distinguishing measurement of strain and temperature along optical fiber in local optical fiber composite submarine power cable was realized. The problem of distinguishing measurement of strain and temperature along sensing optical fiber in field was solved finally.3. The general mechanical tests such as coiling, tensile and tensile bending were analyzed in theory. The strain relation equation between submarine power cable and optical fiber in tensile test was established. The finite element model of tensile test was structured and the physical test was implemented. The results obtained from above work indicate that the established equation is correct. Based on thermal field theory, the steady and transient thermal circuit models of submarine power cable were established. The temperature relation equation between submarine power cable and optical fiber was established excluding thermal resistance, thermal capacity and environment temperature. The steady thermodynamic model and relation equation of submarine power cable, optical fiber and ambient environment were established using finite element method. Each temperatue among submarine power cable, optical fiber and ambient environment can be obtained if the other two temperature is known according to the above equation. Finally, the method for calculating the strain and temperature of submarine power cable using strain and temperatue of sensing optical fiber was proposed, which provides the theoretical support for strain and temperature obtainment of submarine power cable.4. Dynamic finite element models of anchor smash and holding were built. The electro-thermal coupling finite element models of ground short circuit and electrical leakage were built also. The distributed data of strain and temperature after above faults was extrated. The features of space distribution and time variation in various faults were obtained, which conquered the large difficulty of physical test implement and data extraction. The above work provides effective data support for submarine power cable fault detection and diagnosis.5. The method for submarine power cable fault detction and diagnosis was proposed based on strain and temperatue distribution of sensing optical fiber. The influence to fault detection caused by system noise and environment temperature was weakened using normalization method. The false alarm rate was reduced using amount and time of data points over threshold and the fault detection and alarm were realized. The fault position can be accurately identified and the fault type can be accurately judged using second order eight dimension coif wavelet analysis which is sensitive to singular points and has time-frequency multi-resolution characteristics. The above work provides an effective and feasible method for engineering application.