Uncertainty Study On Thermal Rating And Conductor Temperature Of Overhead Lines

In the face of new trends and new requirements for the development of the power grid,the existing power grid resources will be fully utilized to improve the transmission capacity of the lines and reduce the transmission cost,which makes dynamic thermal rating become an important smart grid technology.Dynamic thermal rating(DTR)is to determine the capacity of transmission lines dynamically under the real-time weather conditions(wind speed,ambient temperature and wind direction),which can improve the short-term carrying capacity of transmission lines without changing the relevant regulations of the existing power grid.The wind speed has a great influence on accurate evaluation of the current carrying capacity and the conductor temperature of the transmission line,and it is an important environmental factor for dynamically improving the current carrying capacity of overhead lines.However,taking into account the randomness and intermittent characteristics of wind,the wind speed is usually set as a conservative value of 0.5m/s,which is inconsistent with the actual situation and seriously limits the increase of transmission capacity of the line.Therefore,it is necessary to accurately predict the wind speed.The dynamic thermal rating of the transmission lines is affected by many uncertain factors.Among them,the accuracy evaluation of parameters such as the current carrying capacity of transmission line and conductor temperature is particularly important.The current carrying capacity of the transmission line is calculated based on the meteorological monitoring data and the characteristic parameters of the lines combined with the thermal balance equation,which has a certain error.It is not reliable to give the current carrying capacity only,and the uncertainty of current carrying capacity should be given in order to make the evaluation result more accurate.The conductor temperature affects the transmission line parameters,and then affects the system power flow results.The accurate evaluation of conductor temperature is the basis for the accurate evaluation of the power flow.Based on the above analysis,this thesis has done the following work:the first is the short-term wind speed prediction based on the least squares support vector machine,which is based on the support vector regression machine to find the regression relationship between the historical data and the forecast data of wind speed.In order to improve forecast precision,historical data is clustered by cluster analysis,so that the historical data whose changing trend is similar with changing trend of the forecasting data can be filtered out.The filtered historical data is used as the training samples for support vector regression,and the parameters would be optimized by particle swarm optimization.The prediction model is tested with real data,which proves the feasibility and reliability of the model.Secondly,the uncertainty of the dynamic thermal rating of the overhead line is analyzed.The Monte Carlo method(MCM)is used to sample the uncertain sources,and the probability density function of wind speed,ambient temperature and wind direction is established.Through the calculation and analysis of the steady thermal balance equation and the transient thermal balance equation,the steady current carrying capacity,the transient current carrying capacity,the standard uncertainty and the probability distribution of the minimum and maximum values of the current carrying capacity under 95%confidence interval are obtained.The conductor temperature and operational risk of transmission lines under different current carrying values are also analyzed.Monte Carlo method(MCM)for estimating uncertainty reduce computational complexity,increase computational speed,and increase the validity and reliability of uncertainty assessment.Finally,the uncertainty of system power flow results considering conductor temperature variation is analyzed.Through random sampling data generated by Monte Carlo,the conductor temperature and operating risk under different current carrying values are studied respectively based on the CIGRE standard thermal balance equation.Through calculation model of transmission line impedance considering conductor temperature variation and the system power flow model,based on the 14 node system,the conductor temperature and the system power flow are studied,including the voltage amplitude,the phase angle,the active reactive power and the active power loss and so on.The Monte Carlo method can accurately assess the uncertainty of conductor temperature of transmission line.Accurate conductor temperature can be used to obtain accurate line parameters,and accurate power flow results can be obtained by accurate line parameters.