Over load shedding scheme to increase transient stability limit of Jawa Bali power system network

Indonesia consists of many isolated power system networks. Jawa Bali power system is the main power system networks in Indonesia. Its load is nearly 80 % of total Indonesia. The highest peak load of Jawa Bali power system is 17,211 MW occurred in November, 4 2009. Total available capacity of the generation is 21.296 MW. Jawa Bali power system consists of 2 big sub-systems, Eastern and Western. Eastern sub-system has more and cheaper generation supply than load but Western has in contrary. It causes a big flow from East to West in 500 kV backbone level. In 500 kV level, the flow is congested in Ungaran-Mandirancan Transmission Line that has about 250 km circuit long. The transient stability limit of the transmission line is much lower than its thermal limit. It causes system operator (dispatcher) has to operate more expensive generation unit in Western area even to shed certain load when stability limit of the transmission line is exceeded. Furthermore, it increase a lot production cost of electricity in Jawa Bali. This paper will describe about implementation of over load shedding scheme in Ungaran-Mandirancan 500 kV Transmission Line to increase its transient stability limit. The scheme is designed to enable more flow of power from Eastern to Western sub-system and to decrease the production cost of generation. It uses the logic combination of Out of Step, Over Current, and Pilot Protection. Since this scheme needs calculation of rotor angle it uses out of step protection that usually used in power plant. This is the first scheme being implemented in Jawa Bali power system using this kind of logic. This paper will also describe the study behind this scheme and additional network technology to implement this scheme. Finally, this paper will tell about experiences in operating this scheme and lesson learned from these experiences.