Method Of Dynamic Ampacity Margin Estimation And Operation Risk Warning For Overhead Lines In Time-varying Weather Conditions

The ampacity and operating temperature of overhead lines are affected by the time-varying meteorological conditions.Especially in continuous high-temperature weather during summer,air conditioning load has surged.Therefore,the grid load has hit record highs,and the power equipment has operated under heavy load.The operation and maintenance of power grid needs to pay more attention.The overhead line is the main medium for power transmission.Because the heat dissipation condition of conductor approaches or exceeds the design meteorological conditions in high-temperature weather,the conductor temperature rises,and the ampacity of conductor decreases as the safety margin.The risk of touching trees is increased,which is caused by the increase of sag and the insufficiency insulation distance due to temperature rise.Consequently,it is necessary to study the dynamic ampacity margin assessment and operating temperature warning of overhead lines when meteorological environment changes over time,which can provide important reference for grid dispatching and guide the safe operation of the power supply section in different meteorological conditions.The main contents of this paper are as follows:a)On the basis of comparing the ampacity and temperature calculation method of overhead lines,the calculation model of conductor transient temperature rise in time-varying meteorological environment is derived.Based on the thermal balance equation of conductor,this paper not only proposes the calculation method of the continuous ampacity of overhead lines when the meteorological conditions change,but also concludes the calculation method of the operating temperature of conductor with knowing ambient weather parameters and line currents.In addition,the calculation method of the conductor transient temperature rise response of step current due to current transfer is proposed.The above methods provide theoretical approaches for dynamic ampacity margin assessment,operating temperature warning,and N-1 safety check for heavy load section in high-temperature weather.b)A method for evaluating the dynamic ampacity margin of line based on the numerical weather prediction is presented.The maximum ampacity of line is mainly affected by meteorological conditions.The key meteorological parameters influencing the ampacity of overhead line are analyzed.On this basis,the prediction method for dynamic ampacity margin of lines considering the fluctuation range of numerical weather prediction is proposed.The effectiveness of the proposed method is verified by a case.The operation mode of power systems in high temperature weather is determined,according to the predicted current carrying capacity and ampacity margin.c)A method of N-1 online safety check for power supply section and temperature rise warning of overhead line is proposed.To find the weak point and reduce operation risk of power system,N-1 safety check for power supply section is the basic requirement.Based on the conductor transient thermal balance after power flow transfer in N-1 mode,the ampacity margin and the operation temperature margin of the conductor are checked through real-time weather parameters respectively,and an warning will be issued according to the overload tolerance time of the conductor temperature rise.According to the check results,the suggestion of reducing the risk for power supply section under high temperature and heavy load is proposed.The studied case shows that the proposed method is accurate and effective,which is helpful to grasp the safety margin change progress of the overhead line in N-1 mode,also to take measures to reduce the risk in advance.