A Special Protection Scheme Against a Local Low-Voltage Problem and Zone 3 Protection in the KEPCO System

This paper presents a special protection scheme, which was established in the KEPCO (Korea Electric Power Corporation) system, against a critically low voltage profile in a part of the system after a double-circuit tower outage. Without establishing the scheme, the outage triggers the operation of a zone 3 relay and trips the component. This sequence of events possibly leads to a blackout of the local system. The scheme consists of an inter-substation communication network using PITR (Protective Integrated Transmitter and Receiver) for acquisition of the substations' data, and under-voltage load shedding devices. This paper describes the procedure for determining the load shedding in the scheme and the experiences of the implementation.