Interpretation of remote backup protection operation for fault section estimation by a fuzzy expert system

A hybrid intelligent system, combining neural network modules with a fuzzy expert system, is employed for fault diagnosis in power transmission systems. The artificial neural networks model the protection system of every equipment and the fuzzy expert system analyses their outputs in order to identify the power system section where the fault occurred. Each neural module classifies the fault, according to the information on protection devices and circuit breaker events, in internal, external or lack of information. External fault classification is related to the operation of remote backup protection or pilot relaying starting units responsible for detecting faults outside the protected transmission line. The expert system's inexact reasoning deals with the imprecision of distance relay reach, besides considering information on the operative state of the main protection, for instance, if it is in maintenance. The hybrid method allows to infer the faulted component by mapping the fault direction determined by the relay operation.