Development of Sequential Calculating Type Autonomous Stabilizing Controller for Maintaining Transient Stability in Case of Backup Relay Operation in Load System

A new autonomous stabilizing controller (ASC) has been developed, which is based on the concept of using only local information measured at the substation where ASC is installed. ASC prevents the power system from wide-area blackout by shedding generators optimally when a serious fault occurs in 154-kV-or-below voltage power system and is cleared by backup relay. ASC consists of three functions: a function of detecting faults and judging of starting stability calculations (the first function), a function of calculating power system stability (the second function), and a function of selecting optimal generators to be shed (the third function). The first function composes a signal to start stability calculations when a fault cleared by backup relay is detected. According to the starting signal, the second function executes stability calculations based on equal area criterion. If the result of stability calculations is instable, the third function selects optimal generator to be shed by considering not only stabilizing effect but also quickly restoration after shedding. This paper presents the total algorithms applied in ASC.