Research On On-Line Fault Monitoring System Of Xlpe Cable Based On Distributed Temperature Measurement

With the rapid development of China's cities,the increasing power load,the scale of urban power grid is increasing.Due to the rationality of urban layout,people's demand for urban beauty and the limited land resources,power cable is widely used in urban power grid.Xlpe cable has many advantages,such as simple structure,good electrical and fire performance,large transmission capacity,easy installation and maintenance,etc.,it is widely used in high voltage AC and DC transmission system.Most of the xlpe cables are laid underground by directly burying,pulling pipe,cable trench or cable tunnel,so it is difficult to inspect the concrete operation of the underground part of the cables.If the cable fault occurs in operation,it is difficult to find and locate the cable fault.In order to realize the quick and accurate fault location of xlpe cable,an effective means of on-line cable monitoring is needed.The cable temperature is an important parameter for detecting the running state of the cable,so on-line monitoring of temperature is an effective method.Compared with common temperature sensors,distributed optical fiber sensors have many advantages,such as high temperature resistance,less electromagnetic interference,long transmission distance,high bandwidth,anti-stretching and anti-corrosion.Distributed optical fiber thermometry,optical fiber is not only a conductive light ground element,but also a measured sensing element,based on photoelectronic technology,weak signal detection technology and computer technology,using light as the carrier,using light intensity and phase changes to measure,wide temperature range.In this paper,a cable fault monitoring system based on distributed optical fiber temperature measurement is designed.The real-time distributed measurement of cable skin temperature is realized according to Raman scattering effect,and the abnormal temperature is detected in time,the principle of optical time domain reflection is used to locate the fault point of the cable in time,and measures are taken at the best time to improve the security and reliability of the running cable.In this paper,the theory of cable distributed optical fiber temperature measurement is introduced,the light Brillouin scattering,Rayleigh scattering and Raman scattering are discussed,and the calculation method of Raman scattering light signal demodulation is deeply studied,the theory of optical time domain reflection location is introduced in detail.Then the basic structure of xlpe cable is described,the heating principle of xlpe cable and the thermal circuit model of cable are analyzed,and the calculation model of cable conductor temperature is established.Through the software simulation,the earth temperature of the cable conductor and the outer sheath is analyzed and determined.The Earth temperature of the Outer Sheath of the cable can be used to measure the inner earth temperature of the conductor.Finally,an on-line fault monitoring system for xlpe cable is built.The whole monitoring system is mainly divided into distributed temperature measurement and fault alarm,including front-end data acquisition and transmission,control terminal data processing and analysis,fault location alarm,the xlpe cable fault on-line monitoring system is tested.