Study Of Flashover Operation Risk Assessment Of Transmission Line And Its Related Techniques

Economy rapid development of China puts forward higher and higher requirements to the voltage level of power grid and the reliability of power supply. Voltage grade’s quick development from high voltage to ultrahigh voltage, even extra-high voltage and power grid’s spreading wider and wider make pollution flashover of power system happen frequently, which seriously influences the reliability of power supply and also brings about giant economic loss. According to the statistics, under current voltage level, the economic loss invited by pollution flashover is 10 times than the sum caused by lightening strike and operation over-voltage.In this paper, the problems about forecasting method of equivalent salt deposit density (ESDD) predicting means of critical flashover voltage, influences pollution flashover posing on transmission lines operation reliability and anti-contamination decision-making are explored.The main works in the paper are detailed as follows:1) The paper originally puts the on-line meteorological&ESDD data offered by Optical Sensor System for the ESDD Monitoring of Transmission Equipment into the modelling of ESDD forecasting; uses Grid Search Method to determine parameters(γ,σ) of Least Squares Support Vector Machines(LSSVM); adopts Wavelet Neural Network constructs a new nonlinear combination ESDD forecasting model whose regards the outputs of Multivariate Linear Regression (MLR), BP Neural Network (BP)and LSSVM as the inputs, and the ESDD as the outputs. The method provides a new thread for the computerization of pollution distribution map of power network.2) The article takes use of Powell Searching Operation and Chaos Optimization to modify the traditional Differential Evolution(DE) and uses the modified DE (MDE) to optimize smoothing factor of General Regression Neural Network (GRNN). Based on the data derived from experimental measurements and amathmematical models, a new critical flashover voltage forecasting model using GRNN-MDE is built. The model uses the four characteristics of insulator, namely, diameter, height, creepage distance and form factor, and ESDD as the input parameters.3) A combination of flashover risk prealarming technique with the operation risk assessment of power system is carried originally out. The paper puts forward operation risk assessment theory and index system of transmission line considering of flashover probability. First, the theoretical presentation of operation risk assessment theory considering of flashover probability is defined; secondly, under a certain operation voltage, a model of flashover related probability of insulator is established; third, flashover severity is defined to the weighted sum of the severities of voltage limit violation, frequency limit violation and overload; finally, WSCC-9 proves the efficiency of the proposed mathematics model.4) Fuzzy C-means Clustering (FCM) and Decision-making Mthod Bsed on Gay Degree and TOPSIS are originaly adopted into anti-contamination decision-making. First, based on the results of risk assessment of Chapter 4, all the transmission lines are clustered into three classes, namely, high risk line, middle risk line and low risk line by using FCM; second, combined with the ESDD forecasting results of Chapter 2, five anti-contamination decision-makings are established; finally, to the middle risk lines, in order to consider safety and economy, Decision-making Mthod Bsed on Gay Degree and TOPSIS is introduced to reasonably make anti-contaminations.