One of the main issues concerning the Inverter based Distributed Generators (DGs) is the possibility that inverters could feed parts of the public grid, even when the grid is disconnected from the main power system. Such a condition, that is called unwanted island, is potentially critical both for safety and for consumers' operations. In order to avoid unwanted islands, it's mandatory equipping the generating plant with an Interface Protection (IP) which has to detect the islanding condition and, in this case, to disconnect the generator from the public grid. Several methods for identifying island condition have been proposed, both passive and active, each one characterized by its pros and cons. The standard IEC 62116 was promulgated with the aim of regulating a test procedure to evaluate the IP effectiveness of PhotoVoltaic (PV) inverters independently from the island detection method implemented. The paper discusses the test procedure proposed by the standard IEC 62116 and presents some experimental activities developed by RSE spa, aimed at the assessment of test feasibility and effectiveness.

The Italian MV networks voltage quality monitoring system has been collecting power quality data since 6 years by 600 instruments, 400 of which installed on HV/MV substations MV bus-bars and statistical representative of the network, the other 200 installed at some nodes of the MV lines [1]. The paper is focused on the analysis of voltage dips monitored at some of the 200 measuring points considered more significant. The aims were to confirm, on a wider scale, the representativeness of the statistics gathered on the HV/MV stations MV bus-bars with respect to that expected along the MV lines and to investigate the events way of propagation along different voltage levels. The analysis has been performed by both statistical methods on real data and DIgSILENT 1 simulations. The possibility to get the MV network voltage dip performance along the lines by measurements at HV/MV stations level has been widely confirmed. Measurements at MV lines have also confirmed the percentages of probable HV origin voltage dips, evaluated at national and macro area levels. The voltage dips duration distributions have shown a good accordance with the typical tripping times of the HV and MV protection system.

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