Load Risk Modeling And Prediction Of Overhead Transmission Lines Under Severe Weather

Overhead transmission line is an important part of power system and is also the main artery of power transportation.The safe operation of the power grid is closely related to the safe operation of overhead lines.When overhead lines expose in the natural environment for a long time,they are easily affected by strong winds,snow and ice storms,cold freezing and other adverse weather effects.The occurrence of a variety of adverse weathers will lead to wires disconnection,towers collapsing and other serious cases.As a result,a large area of power outages would occur.It is a very important practical significance to establish overhead line risk assessment and early warning system,which can ensure the safe and stable operation of transmission lines.At present,the researches on the risk assessment of overhead lines mainly focus on the iced-influence on the lines,there are few researches on the reliability of overhead lines in extreme weather.This paper considers the ontology of overhead lines as the investigative subject.According to the line-load-calculation theory,risk-assessment theory and fuzzy-forecasting theory,a risk assessment model of overhead lines in extreme weather considering to temperature-change influences can be established,and overhead line load risks can be predicted under three extreme weather conditions,including iced-wind,storm and wind.Finally,the cases in the MATLAB environment demonstrate the correctness of theories and methods proposed in this paper.This paper includes the following three aspects:1)Equivalent load modeling of air-temperature difference on overhead transmission lines.Based on the basic theory of overhead line design,the state equation of overhead transmission lines is deduced in detail.Then a group data pair of both air-temperature difference and the specific load change can be obtained by the state equation.By the least square method,the equivalent load calculation formula to the air-temperature difference of overhead transmission lines is established.2)Risk assessment of overhead transmission line in extreme weather.It is assumed that both the strength and the load of the overhead line obey the normal distribution.Through the analysis of joint probability density function of the overhead line,combined with the line-load-strength random characteristics and the stress-intensity interference theory,the load risk levels for overhead lines in three extreme weather conditions can be evaluated.3)Fuzzy prediction of overhead transmission line load.According to the failure probability of overhead lines,load states of overhead lines is divided.In the light of the load states,the fuzzy input variable membership functions involving rainfall intensity,wind speed and ice thickness are established,a membership function of fuzzy output variable is defined at the same time.Based on GA-TS-FNN model,the load values of overhead line are obtained by fuzzy inference.On the basis of the predicted load value,the load risks of overhead lines are evaluated,and effective warning information is announced.At the end of this paper,the accuracy of the models and the correctness of the proposed methods are verified by an example.It has important practical significance and practical value for the safety analysis of the overhead transmission line.