Maximum entropy probability method applied to assess voltage sag frequency due to transmission line fault in the electric power system

Voltage sag caused by faults on an electric power transmission line is one of the most intractable power quality issues for both utility companies and customers. The fault in power system randomly exists along transmission lines due to the combination of many uncertain factors. To predict and assess the annual expected sag frequency (ESF) deriving from the faults along lines, a stochastic‐based method that employs maximum entropy principle, namely the maximum entropy probability method (MEPM), has been introduced in this paper. Moreover, various types of faults have been considered systematically. With the fault line intervals and the sample moments taken into account, the discrete values of distribution probability of fault locations along the transmission lines have been estimated by means of the MEPM. For a given voltage sag magnitude corresponding to the voltage tolerant level of sensitive equipment at the tested bus, the ESF has been calculated in view of the statistical fault rates of interrelated transmission lines. The implementation and application to a classical five‐bus system and IEEE RTS‐30 test system have been presented consequently. The simulations have revealed that compared with the four existing methods, the MEPM is accurate, flexible, and immune of round‐off errors, and therefore it can be widely applied to the various aspects of power systems. Copyright © 2009 John Wiley & Sons, Ltd.