Research On Temperature Distribution Of Power Cable Joint And Its On-line Monitoring System

The cable intermediate joint is an important part connecting the two cables and the weakest link in the power line.There may be contact resistance or defects in the manufacture or installation of cable intermediate joints,resulting in local temperature rise.In addition,The high flow rate in the actual operation will increase the joint temperature,accelerate insulation aging and shorten the service life of cable joints.This poses a threat to the stable transport of electricity.Therefore,on-line monitoring of cable joint temperature has a strong practical significance.In this paper,the structure,fault and heating mechanism of cable and cable joint are described at first,which provides a theoretical basis for numerical calculation of temperature field of cable intermediate joint.The temperature measurement experiment platform of 35 kV cold-shrinkable cable intermediate joint is built.The surface temperature of cable intermediate joint is measured by infrared imager in multi-angle.The optimum temperature measuring point is obtained by analyzing and comparing the temperature distribution on the outer surface of the intermediate joint under different current.At the same time,the temperature sensor is installed at the conductor junction and the conductor of the cable,and the temperature of the conductor under different current is measured in real time.Based on the measured temperature data of the outer surface and conductor,BP neural network is used to predict the conductor temperature from the surface temperature.Then the geometric model of cable intermediate joint with ideal condition?contact resistance and internal defects is established.The temperature field simulation and current carrying calculation are carried out by using ANSYS software.The results show that with the increase of contact resistance,the temperature of the joint core increases gradually,and the axial temperature of the joint core and exterior surface decreases gradually from the center position to the two sides.When there are air gap,water droplets and conductive particle defects in the cable intermediate joint,the temperature distribution of the joint changes.And the larger the air gap size,the greater the influence on the local temperature.By comparing the finite element simulation data with the experimental data,the relationship between the conductor temperature,the external surface temperature and the load flow is studied.That provides theoretical support for 35 kV cable intermediate joint of the temperature on-line monitoring of the sensor distribution point and the temperature early-warning value of each point.Combined with the experimental and simulation results,the design scheme of the on-line temperature monitoring system for cable joints is given.The temperature sensors are arranged in the cable intermediate joint in the form of "dot matrix".The ZigBee wireless communication network is constructed based on the Z-stack protocol stack.The long-distance transmission of temperature data is realized by GPRS.And designed the PC interface,it can display real-time temperature measuring point temperature,draw curve,early warning,etc.The system can not only determine the local overheating of the cable joint in time,and find the potential safety hazard of the joint,but also has the advantages of strong portability and low cost.