Calculation Model Of Equivalent Ice Thickness Based On Overhead Transmission Line’ Dynamic Load

Transmission line icing is a serious problem that affects the safe operation ofpower systems. The accidents caused by icing, such as line disconnection, tower failure,and transmission lines galloping, seriously threaten the security and reliability ofelectric power networks.How to effectively predict the ice thickness and accurately monitor the icingprocess on the conductors has become an important research topic at home and abroad.It is very meaningful and vital for power grid to take timely anti-icing and de-icingmeasurement to avoid the occurrence of ice disaster. Many prediction models andmonitoring methods for transmission line icing have been proposed by many scholars.However, due to the complexity of the ice progress and inaccurate measurements of themodel parameters, the accuracy of the models has been questioned, and they are notwidely used in engineering. Therefore, to establish an accurate and efficient model forthe transmission line icing has important theoretical value for the power grid to designand construct anti-icing mitigation project. Additional, it can provide a reference for therelevant departments to take timely and reasonable anti-icing or de-icing measures.Supported by the National Basic Research Program of China (973program)(“transmission line icing failure forming mechanism and prediction model and controlmethods”) and the cooperation program (“early warning program and calculationmodel for transmission line icing”) with the EHV Maintenance Test Center of ChinaSouthern Power Grid, theoretical analysis and modeling, field observation andmeasurement and actual operation transmission lines tests are used to carry out theproject. The concrete research content is as follows:A long-term of observations and measurements are carried out in the XuefengMountain Natural Icing Stations (XMNIS) and the influence factors of the natural icingon the transmission lines are analyzed. Moreover, the typical section shape of glazeicing on conductors is studied and the correction coefficient of the actual non-uniformice is proposed as an accurate and convenient method for field icing measurement.Based on a lot of field measurement at XMNIS, the shape correction coefficient of thetypical glaze icing is analyzed and calculated.The wind load theory and the formula of the load calculation are analyzed. And theuse of harmonic synthesis simulation of fluctuating wind load in the time-domain method for modeling wind load is studied. The empirical formula and the aerodynamiccharacteristics calculation method of the trnansmission line wind load are studied andanalyzed. Moreover, a new method for wind load calculation is presented based on thechange of the transmission line load characteristics. Based on the data gathered atXMNIS, the wind load is calculated and compared with the results by empirical formulawhich verifies the correctness and feasibility of the proposed method.Based on the hydromechanical theory, the modeling method and the simulationmethod for the analysis of the aerodynamic properties of the crescent iced conductorand sector-shape iced conductor are put forward. The air flow map around the icedconductors is simulated. Besides, as to the iced conductors with different ice thicknessand wind speed, the lift coefficient and drag coefficient under different attack angles arecalculated. The influence law of ice thickness, wind speed and different cross sectionsof the iced conductor on the aerodynamic parameters of iced conductors can beobtained.The basic characteristics of the tension and tilt of the insulator string at the tangenttower after icing are analyzed. Based on the parameters of tilt and tension of theinsulator string at the tangent tower, a new mechanical calculation model is put forwardwhich considers the combined ice and wind loads.Based on a long-term observations and a great number of field experiments at theXMNIS, the proposed model is verified. Moreover, based on the implementing programby C++, the proposed model is applied to the actual transmission line. The on-linemonitoring data and field ice data obtained from the actual operation transmission linesof the China Southern Power Grid are used to verify the proposed ice thicknesscalculation model.