Development Of Monitoring System And Experimental Research On Overhead Transmission Lines Based On BOTDR Technology

In our country, the strategic project of "West-East electricity transmission project, North-South sending each other, National network" has entered the building and implemented stage, most of the long-distance overhead transmission lines need to cross high altitude, ice coating, and mountain forests areas. These areas cause the overhead transmission lines under harsh environments, such as wind, rain, snow, ice, thunder, fires. The overhead lines would be affected by the role of electrical, thermal and mechanical load in long-term running, which cause the fault defects of the wire aging and the break. There is a serious threat to the safe and stable operation of the entire transmission system. Therefore, it is very important to monitor the operation state of the long-distance overhead line in real-time, reliably and effectively.At present, many equipments used in transmission line condition monitoring are resistive sensing sensors, which have many shots, such as susceptible to electromagnetic interference, short service life, can be restricted and lower reliability of long period running. With the development of optical fiber technology, the fiber bragg grating sensing device has got a certain application in transmission line monitoring with its small size, high sensitivity, performance is not affected by electromagnetic interference, measuring distance and can not take the advantages of the limit. But the manufacturing process is complex and can’t realize distributed monitor. The distributed optical fiber sensing system not only has all the advantages of the fiber bragg grating sensing device, but also can realize distributed continuously measure. This paper conducted in-depth research on the theoretical and experimental aspects of the brillouin distributed optical fiber sensing technology. The main contents and results were as follows:(1) This paper aimed to detect the brillouin shift weak signal cost-efficiently and demodulate the broadband, and used the coherent detection scheme based on brillouin frequency shift,a distributed optical fiber sensing system(BOTDR) prototype based on brillouin scattering was developed. The experimental results show that, the maximum sensing distance and the spatial resolution of the system are 30 km and 10 m respectively. The temperature measurement range and the resolution of the system are-60℃—90℃ and ±2℃ respectively. Within the range of sensing distance can monitor the strain information.(2)This paper used an ordinary single mode fiber instead of electricity optic cable for the fault simulation monitoring tests.The results shown that when the different types of failure occurred,the developed fiber optic sensing system would show different curves.(3)This paper performed a temperature test of OPGW cable in the substation field.the fiber-optic sensing system could monitor the temperature of on-site overhead lines distributed, which results are basically in agreement with the local temperature trend and are also consistent with the temperature profile of the FBG sensors monitoring in a position, and the biggest difference is 1.8℃.And the paper analysed the problems encountered during field test, it has provided a reference for the application of the distributed fiber optic sensing technologyusing in the transmission line engineering.