High-voltage Cable Temperature Monitoring Research Based On Raman Distributed Optical Fiber Sensing

As an important carrier for power transmission,the stable operation of high-voltage cables helps to guarantee the quality of power supply and improve the safety and reliability of transmission lines.Existing high-voltage cables have usually been in operation for more than decades,leading to frequent accidents in high-voltage cables and intermediate joints due to their own poor quality,external damage,insulation breakdown and other problems.Leakage current increases the loss of high-voltage cable conductors,and the additional heat generated accumulates inside the faulty cable,causing the temperature to rise and eventually lead to explosive accidents.At present,the main difficulties of high-voltage cable temperature monitoring and condition assessment include:(1)high-voltage cable temperature monitoring mainly uses thermal infrared imaging technology,spot temperature sensing technology and optical fiber sensing technology,which usually only focus on the problematic parts of the line,while the location of the high-voltage cable fault has a random nature,so the above methods can not achieve high-precision distributed temperature measurement;(2)the existing monitoring methods can only achieve the temperature monitoring of the high-voltage cable surface skin,it is difficult to directly assess the operating status of the cable and intermediate joints through the conductor temperature.In order to provide more accurate monitoring of highvoltage cable temperature and support the evaluation of its operating status,this dissertation will focus on the analysis of temperature characteristics and status evaluation of high-voltage cables and intermediate joints,and conduct experimental research on distributed optical fiber Raman temperature monitoring.The specific research work is carried out as follows.(1)Non-invasive monitoring of high-voltage cable conductor temperature is achieved by using Raman distributed optical fiber sensing technology and combining electromagneticthermal coupling temperature analysis method.Firstly,a simulation model is built by the finite element analysis software COMSOL to solve the temperature distribution when the electromagnetic field and heat transfer field are coupled,and then analyze the influence of ambient temperature and load current on the temperature distribution of high-voltage cable;on the basis of obtaining the relative temperature change law between the high-voltage cable surface and conductor,the calculation formula of high-voltage cable conductor temperature is derived.Using the self-developed Raman distributed optical fiber sensor(temperature measurement accuracy ±1.00℃,temperature resolution 0.50℃,spatial resolution 1.0 m)to carry out temperature measurement experiments on the 100 m long,110 kV high voltage cable in the cable trench of Yanzhong Line in Yuncheng City;the highest temperature of the outer surface of the high voltage cable is 24.29℃,and the absolute error of the corresponding high voltage cable conductor temperature is 2℃.(2)Aiming at the problem of abnormal temperature of high-voltage cable intermediate joints,a study was conducted to evaluate the state of crimp defects.Firstly,the equivalent heat loss of high-voltage cable intermediate joint is solved by finite element analysis,and the temperature change law of the joint in both ideal and equivalent states is analyzed;the contact coefficient k is introduced to characterize the crimp defect status,and the study shows that when the contact coefficient k>2.7,there is a large contact resistance and the conductor temperature reaches the safe working temperature of 90℃,which is a crimp defect safety hazard.Zigbee technology is used to design an experimental scheme for monitoring crimp defects in highvoltage cable intermediate joints,and an interactive control interface is developed based on LabVIEW to realize the fault warning of high-voltage cable intermediate joints.