Research On Fault Probability Model Of Overhead Power Transmission Line Based On Environmental Factors

As an inevitable trend of power system, robust Smart Grid plays indispensable role by assisting control center controlling expanding comprehensive power grid, which definitely require control system to improve its abilities on sensing system status ? discovering potential risk and predicting future patterns. These are not accessible unless equipment fault level is assessed every moment, in which the overhead transmission line faults takes up over 90%. This paper is focused on the research of overhead transmission line fault probability system.Firstly, several line fault probability models, which aim at simulating faults of different weather conditions, are built up after analyzing the features and regularities of fault reports from state grid. By comparing existing line fault simulating methods, those with high efficiency, feasibility and accuracy are selected to form up the line probability models. Some of them are improved to suit the power system online control requirements.An advanced EMTP travelling wave algorithm is proposed to estimate the inverse flashover probability. Tower models are set up in an EMTDC software and tested with different striking schemes, with corresponding probabilities are save in matrices. This method can efficiently assesses the inverse flashover probabilities by looking up similar scheme's result in matrices. This method is combined with EGM method to form up lightning stroke probability model.Also, the Subjective Bayes algorithm is firstly used to consider wind fault probability. Pressure distribution field is set up before calculating wind velocity using amended gradient flow equation. After correcting wind speed based on local landscape, fuzzy system are called for evaluating wind and line excitation. CP equation is then used to update historical wind fault probability to posterior probability.Besides, an advanced icing thickness model is proposed for the icing fault. Based on the thermal equilibrium equation, line icing condition is judged as accretion or melting. The Makkonen ice accretion model with consideration of capture and frozen coefficients can derive ice cone growth, while melting ice weights can be obtained from thermal equilibrium equation. Mechanical analysis is executed to estimate the wire breaking risk, with tower collapsing, wire swing and icing flashover risk are calculated as followed.Flashover voltage model of insulator is carefully selected after comparing exsiting algorithms, and function fitting algorithm is chosen as the proper one. The flashover probability is then calculated based on obtained flashover voltage.After all, the transmission line fault probability model is formed up by combined all occasionally specified models by using concatenation logic equations. A complete set of environment threshold parameters is applied to switch on proper conditional probability models for efficiency.In addition, the aging effect on power transmission line is discussed, and a health condition evaluation method is introduced and applied to form a novel algorithm to consider aged equipment parameters. An example comparing new and aged tower collapsing probability under icing conditions is shown to prove the necessity of considering aging effect.In the end, the complete line probability model is applied to calculate the line fault probability of a coastal province power grid in the Eastern China in 2013. Some periods of time, which have severe weather, are chosen as the simulation time, and corresponding weather and system data are used to formed simulation environment. The results testify the accuracy and feasibility of the line probability model. Finally, the importance of power transmission line probability model is discussed in power grid system evaluation process.