Conventional overcurrent protection schemes for radial distribution systems usually attempt to coordinate a recloser at the beginning of the feeder with the fuses on the laterals. The integration of distributed generation in distribution systems leads to problems related to protection coordination that are difficult to be solved by applying conventional protection techniques. This paper proposes an efficient communicationbased protection scheme that implements common directional overcurrent relays instead of reclosers at the line, assisted by intertripping and blocking transfer functions. The proposed protection strategy guarantees selectivity regardless of whether the generating units are connected to the network or not, and can be designed retaining either the fuse-blowing or fuse-saving philosophy. Meaningful conclusions are derived from the application of the scheme on a test distribution system.

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Index Terms-Electric-and magnetic-field measurements, extremely low frequencies, indoor power distribution substations, safe public and occupational exposure.

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SUMMARYThis paper investigates the results of the distributed generation penetration in a weak medium voltage power distribution network. The connected distributed generation resources are in their entirety small hydroelectric plants. Their locations are predetermined. Specifically, the influence of distributed generation on the network branch currents and voltage profile as well as on the short-circuit level at the medium voltage busbars of the infeeding substation are examined using a commercial-grade software package. The arising problems are explored and alternative technical solutions to deal with them are proposed. Finally, an initial proposal for an optimum distributed generation penetration in the predetermined network positions is given. A real-world study case, rather than a simplified academic network, is selected to be analysed in order to specify, as accurately as possible, the arising practical problems and to use this experience in the future in the development of a fast and reliable method for the determination of optimal distributed generation allocation in random network positions.