© The Institution of Engineers, Sri Lanka 1 A New Scheme of Under Frequency Load Shedding and Islanding Operation

Abstract: Emergency load shedding (LS) for preventing frequency degradation is an established practice all over the world. The objective of LS is to balance load and generation. This paper presents a technique to develop a reliable LS scheme to prevent black-outs, while maintaining stability in power systems (PSs) with high variability and uncertainty under abnormal conditions. Different techniques are available for implementing LS schemes such as traditional, semi-adaptive and adaptive. The LS scheme proposed in this paper has a sequence and conditions of applications of different LS schemes and islanding strategies. The proposed technique comprises with two Phases. During Phase-I, a LS methodology that was based on traditional & semi adaptive LS schemes was implemented and in Phase-II an adaptive LS scheme was implemented. With this methodology, instead of shedding pre-set loads, the disturbances are shared among the loads. The effectiveness of the developed scheme was investigated by simulating different abnormal conditions in the power system of Sri Lanka. The tendency for a total PS collapse could be eliminated with the suggested scheme which is sensitive to such factors as generation & demand of the PS dynamically, while maintaining stability in PSs with high variability and uncertainty