An Equivalent Heat Transfer Measurement Method For Evaluating Ampacity Of Overhead Transmission Lines

The conductor ampacity is an important parameter index for evaluating the transmission capacity of transmission lines.With the rapid economic development,the demand for electricity in some areas has also grown rapidly,and the problems of heavy overloading and peak-shifting power curtailment are still very prominent due to the restrictions of the grid structure.On the basis of the existing transmission grid and traditional conductor ampacity control methods,it is difficult to provide a solid and stable power supply to the rapidly developing national economy.Therefore,the method of evaluating ampacity based on the dynamic thermal rating(DTR)technology is more and more important to improve the transmission capacity of the existing transmission lines.However,the existing DTR models have some shortcomings.The existing technology generally indirectly calculates the real-time dynamic ampacity of the conductor by measuring many parameters such as ambient temperature,sunshine intensity,and wind speed.It involves many sensors and has problems such as large measurement deviations.There are also some technologies that measure the temperature,sag or tension of the conductor to evaluate the DTR.There are problems such as the need to install sensors in the power outage and the difficulty of on-site implementation.In order to promote the practical process of the DTR method,it is necessary to overcome the shortcomings of the existing technology and provide a DTR method with convenient measurement,good real-time performance,significant effect,high stability,and low implementation difficulty.This is of great significance to the safe and stable operation of transmission lines.Based on the in-depth analysis of the related research on the heat transfer of overhead conductors,this paper intends to study the heat loss of overhead conductors,determine the ampacity of overhead conductors,and evaluate the capacity of overhead transmission lines in practical applications to achieve DTR of overhead transmission lines.The main research work carried out in this paper is as follows:1.Analysis of the influence of meteorological factors on the ampacity of conductors.Various methods of calculating the ampacity based on the thermal balance equation of overhead conductors are introduced and summarized.The formula for calculating the ampacity of conductors is determined,and the comprehensive and individual influences of meteorological factors on the ampacity of conductors are analyzed.2.A DTR model for overhead conductors is established based on the equivalent heat transfer(EHTM)method.According to the Reynolds number related to wind speed,the correlation function of overhead conductors and aluminum(Al)ball is established.The correlation between the overhead conductors and the Al ball convection heat dissipation process is determined.Then,a DTR model of overhead conductors,an EHTM model,which can replace wind speed measurement is established.3.Simulation study of EHTM model based on heat-fluid coupling.First,a heat-fluid coupling finite element simulation model is constructed,the applicable conditions of the EHTM model are analyzed,and the accuracy of the EHTM model is verified.Then,according to the structural model of the EHTM equipment in practical application,the finite element model of the Al ball in the equipment is established,and then the influence of the structure difference on the EHT model calculation of the ampacity of the conductors is analyzed.4.The improvement and experimental research of the EHTM model.The model has been improved in two aspects: the correlation between the conductor and the Al ball,and the experimental correlation parameters of the Al ball.Subsequently,the operation of EHTM equipment is simulated through the established experimental platform.The improved EHTM model is verified by standard.Finally,the sensitivity analysis of the improved EHTM model is carried out.5.Research on the calculation method of sunshine intensity based on the EHTM method.A comparative analysis of several existing methods and strategies for obtaining solar intensities is presented,and a scheme based on the thermal characteristics of double Al spheres is proposed.Finally,using finite element method to simulate the thermal characteristics of the Al ball under different irradiance verifies the accuracy of the scheme.