Research On The Key Technologies Of Ampacity In 110kV Cable Line

With the wide application of high-voltage cables in urban power grids and the increasing emphasis on the utilization and reliability of existing power cable assets by power-related departments,how to more accurately determine the temperature field distribution and ampacity of cable lines has become a hotspot in the field of cables in the past decade.This paper aims to solve some unresolved key technologies for 110 kV cable line ampacity.The main research is as follows:1)Establish a 3D(three-dimensional)thermal network and 3D finite element dynamic ampacity model,consider the axial heat transfer of the cable and the corrugated aluminum sheath structure,determine the radiant heat between the wrapped and the sheath,build 110 kV cable upflow experimental platform,and use the four methods(IEC standard,2D(twodimensional)thermal circuit,3D thermal network and 3D finite element)to obtain the results and the experimental results,the results show that the 3D model has a better accuracy.2)Research the temperature distribution law of the cable skin,propose the axial thermal circuit model of cable skin based on state equation,establish its 3D finite element model(by ANSYS),study the axial path of cable skin in steady and transient state.The axial path of the cable skin,the circumferential path of the section and the temperature distribution of the surface area(temperature range,maximum temperature,temperature extreme value,etc.)are studied,and a reasonable temperature measurement scheme is proposed based on the acquired laws.3)Determine the more accurate calculation model of the cable sheath's current,consider the effect of leakage current on the basis of induced current,propose the current model and its parameter calculation method under normal and sheath multipoint grounding.The accuracy of the theoretical model is verified by the distributed parameter line model with concentrated resistance in ATP-EMTP.4)A numerical calculation model for the connection resistance of the compression connector in cable joint is proposed.Five different compression connectors(120/150/240/500 and 630mm2)are fabricated according to the standard,and four different electrical contact models are combined.The finite element method is used to establish a numerical calculation scheme(empirical formula/Hertz/Greenwood/Bahrami).The verification experiment of the above numerical model is carried out by the AC(alternating current)resistance test platform.The results show that the numerical calculation model based on the elastoplastic contact model of irregular rough surface(Bahrami)has a better accuracy(relative error less than 3.95%).5)Set up a 110 kV plug-in GIS terminal up-flow experimental platform.The experiment found that the axial heat transfer of the GIS terminal is obvious,and the temperature to the high point is the cable conductor at the radial pushing section of the spring.When the load is 1200A(environment 29°C)The maximum temperature of the inner conductor of the GIS terminal is 93.0°C,which is 15.4°C higher than the average temperature of the cable,and has exceeded the ampacity of the cable line.