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Islanding operation in a distribution network connected to Distributed Generations (DGs) has the advantage of being able to continuously supply power to the loads even when disconnected from the grid. However, there are technical issues that need to be solved in order to guarantee a successful islanding operation. The main challenge in the successful islanding operation is to ensure the stability of frequency and voltage of the distribution system. Commonly load shedding schemes are used as a mechanism to stabilize the magnitude of the frequency and the voltage by shedding some of the loads to ensure an adequate balance between generation and loads. This paper reviews recent load shedding schemes focusing on distribution system application. Their respective merits and demerits are presented. Moreover, this paper also highlights the application of Voltage Stability (VS) index for load shedding schemes. A brief overview of the DG with their respective advantages also presented at the beginning of this paper.

This paper presents a load shedding scheme (LSS) based on system frequency and voltage stability (VS). In the proposed scheme, the amount of power imbalance is determined using a rate of change of frequency, and the load shedding priority is carried out based on a VS index. The load with the highest tendency for voltage collapse (based on the index value) is given first priority to be shed. Thus, by shedding the most sensitive load, the distribution system can be saved from power collapse and then the system can return to its nominal state after load shedding. The proposed LSS is validated through simulation using PSCAD/EMTDC software on a Malaysian distribution network that consists of two mini-hydro generators. The simulation results show that the proposed scheme manages to shed the optimal amount of load when compared to conventional and adaptive frequency LSS. Moreover, apart from frequency stability, the proposed scheme also shows a significant improvement in the voltage profile of the islanded system.

This paper presents the comparison between Stability Indexes value used for load shedding of the islanded distribution network. In this work, 2 stability indexes, namely Power Stability Index (PSI) and Stability Index (SI) are used as Stability Index Ranked (SIR) to shed the loads. The proposed Under-Frequency Load Shedding (UFLS) algorithm is implemented the online stability index ranked as main priority of load to be shed. The performance of frequency and voltage are monitored in the existing Malaysia's Distribution network interconnected with two mini hydro generations. The simulation results show that the PSI possesses the better and improved voltage profile rather than SI index, while stabilizing the system frequency.

This paper presents overload alleviation based on real time power flow tracing for distribution networks. The proposed scheme is capable to detect the source of overload at the transformer. Subsequently, load buses will be selected according to the contribution of overload equipment, This scheme also determines possible load to shed. In order to verify the proposed scheme, dynamic simulation is performed on an existing Malaysia's distribution network interconnected with mini hydro generation. The simulation results show it is validity, efficiency and simplicity.