Piecewise equivalent model of ice disaster impact on outage rate of transmission lines using fuzzy expert system

Transmission lines always cross long distance. As different parts of a transmission line may confront different weather conditions at the same time, a piecewise equivalent model is introduced to calculate the outage rate. The transmission line is divided into segments in series according to their particular external environment and their corresponding outage rates. Then these segments are combined to form an integrated outage rate for the entire transmission line. Taken the uncertainty of weather forecast and system operating status into account, the analytical model between load and outage is converted into a fuzzy one. It contains fuzzy sets, membership functions and fuzzy "if-then" rules, to effectively solve the problems caused by inaccurate data. The new model is applied to IEEE RBTS system. Assuming that a specified transmission line confronts three types of external load pressure in different parts, the outrage rates of the transmission lines are calculated and compared. With the deterioration of the weather condition and system operating state, the outrage rates of the transmission lines increase. The proposed model provides of the foundation for operational risk assessments of transmission lines and power system reliability.