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Anti-islanding protection schemes currently enforce the DGs to disconnect immediately for grid faults through loss of grid (LOG) protection system. This greatly reduces the benefits of DG deployment. For preventing disconnection of DGs during LOG, several islanding protection schemes are being developed. Their main objectives are to detect LOG and disconnect the DGs from the utility. This allows the DGs to operate as power islands suitable for maintaining uninterruptible power supply to critical loads. A major challenge for the islanding protection schemes is the protection co-ordination of distribution systems with bidirectional fault current flows. This is unlike the conventional overcurrent protection for radial systems with unidirectional fault current flow. This paper presents a comprehensive survey of various islanding protection schemes that are being developed, tested and validated through extensive research activities across the globe. Chui Fen Ten received the BEng degree from Universiti Teknologi Malaysia, Skudai, Malaysia, in 2005 and the MSc degree from University of Manchester (formerly UMIST), Manchester, UK, in 2006. Currently, she is working towards her PhD degree in the School of Electrical and Electronic Engineering of the University of Manchester (formerly UMIST), Manchester, UK. Prof. P.A.Crossley is Professor of Electrical Engineering at the University of Manchester. He graduated with a B.Sc degree from UMIST, United Kingdom in 1977 and a Ph.D. degree from the University of Cambridge, United Kingdom in 1983. He had been involved in the design and application of digital protection relays and systems for more than 25 years, first with GEC, then with ALSTOM and UMIST and the Queen's University of Belfast, United Kingdom and currently with the University of Manchester. Currently he is the Director of Joule Centre for Energy Research, University of Manchester, UK. He is an active member of various CIGRE, IEEE and IET committees on protection.

This paper presents a simulation study of operation and control of distributed generators (DGs) in power islands in Smart Grid environment. It examines the technical feasibility of DG islanding operation to exploit their services for improving electrical safety, security and quality of energy supply. The grid-connected DGs are initially operated at PQ mode and then switched to V-f mode to have full controllability of bus frequency and voltage when operated as independent power island. Suitable controllers are designed separately for individual control of voltage and frequency at the DG bus. The simulation results are validated through several case studies using DIgSILENT software for both intentional and unintentional loss of grid (LOG) situations. It has been observed that when several islanded DGs are interconnected to form a power island, they can share the active and reactive power demands of the island leading to quick restoration of the system voltage and frequency within permissible bandwidth.

The continuity of power supply can be improved by power system islanding. A possible solution, synchronous islanded operation, enables the islanded system to remain in phase with the main power system while not electrically connected, and so avoids out-of-synchronism re-closure. Specific consideration is required for the multiple-set scenario, and is the topic of this paper. A suitable island management system is proposed, with the emphasis being on maximum island flexibility by allowing passive islanding transitions to occur, facilitated by autonomous control. These transitions include: island detection, identification, fragmentation, merging and return-to-mains. It can be challenging to detect these transitions while maintaining synchronous islanded operation. A Mathworks SimPowerSystems simulation is used to investigate the performance of the island management system. However, return-to-mains is particularly difficult to detect, and so a method based on voltage phase angle variability is explored by using a laboratory demonstration and time stamped phasor measurements.

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