Study On Quasi-dynamic Thermal Rating Of Overhead Transmission Lines

Dynamic thermal rating(DTR),as an important technology to assist the planning and operation decision of smart grid,has become a key choice to solve the problem of insufficient power supply and the problem of transmission bottleneck.Compared with the static thermal rating(STR),DTR abandons the method of calculating the current carrying capacity by using conservative weather.Instead,the capacity of the transmission line is maximally improved based on real-time meteorological data.Due to random variation of real-time weather conditions and errors of meteorological forecast,the value of DTR has great volatility.DTR depends on a large number of sensor deployment,resulting in the higher cost of implementation and the strict requirement for the equipment.This paper considers the reliability and economy of the line carrying capacity assessment,the quasi-dynamic thermal rating(QDR)is used as the maximum transmission capacity of the line in this paper.QDR is constant in the time scale of its definition,QDR has great significance for taping potential and alleviating transmission congestion.First,this paper based on the CIGRE standard thermal rating model of overhead lines,the relevant meteorological parameters and conductor characteristic parameters are introduced,and the sensitivity analysis is carried out for the parameters with high influence level.Combining Runge Kutta method with transient heat balance equation of conductor,the transient and time constant changes of conductor temperature are simulated and analyzed,and the variation characteristic of thermal time constant is analyzed.The time resolution of meteorological parameters sampling is determined.Secondly,on the basis of a clear interrelationship between conductor ampacity and key parameters,a calculating method of QDR driven by meteorological data is proposed,and the meteorological parameters(wind speed,ambient temperature,wind direction)threshold at 90%-99%confidence level are quantitatively analyzed,and the QDR under different time scales(year,seasonal and monthly)is calculated from steady thermal balance equation.Then,the method of operation risk evaluation is obtained.To test the quasi-dynamic thermal rating effect and reliability of implementation,an example to assess the running risk and compatibilization effect under actual operation year is given.Finally,in accordance with the variation characteristics of conductor temperature with change of environment parameter and current based on transient thermal balance,analysis of changes of each branch current under transmission congestion is given.Then,combining the QDR(annual rating,quarterly rating,monthly rating)with the alarm system of transmission congestion management,a transmission congestion management method based on QDR is proposed.A transmission congestion alarm system including the conductor temperature estimation module is designed.The feasibility of QDR in transmission congestion management is verified by an example.