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The amount of distributed generation (DG) connected to medium voltage (MV) networks is increasing, which allows to use MV distribution networks as self-healing networks. Many of the new connected DG units are converter interfaced and not capable of producing high fault currents. It makes using distance protection an interesting option for networks with low or negligible fault current levels. This paper studies the possibilities of using distance protection in normal and island operation of the network. However, the main problem with distance protection is that DG between the measurement point and fault point acts as an intermediate in-feed negatively affecting the accuracy of impedance measurement. Distance protection concept for smart grids in conjunction with islanded operation is being studied in one example case. The results show that distance protection with telecommunication aided adaptive settings can be used to protect islanded self-healing networks with some restrictions on DG location and number.

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As the number of distributed generation (DG) units connected to medium voltage (MV) networks increases the structure of networks is changing and getting more complex. As a result the requirements for protection are getting more and more complicated and are playing an increasingly important role. Protection of DG units with traditional protection schemes causes performance degradation and in some cases sufficient protection levels may become unattainable. In this paper the issues with traditional protection are addressed. The benefits of using of using telecommunication based protection schemes with DG are presented from which the most important advantages are improved selectivity and decreased fault clearing times.