A smart device for islanding detection in distribution system operation

The present paper focuses on the design, realization and validation of the prototype of an innovative relay, named SmartID, for islanding detection in LV distribution systems. The SmartID adopts a patent-pending detection method: it uses local measurements to estimate the parameters of a linear model of the distribution system, which can be used to distinguish grid-connected from islanded operation. The hardware of the SmartID prototype is composed of a voltage transducer, some conditioning stages, a commercial μcontroller and an output stage. The software implements the A/D conversion of the measurements, the phasors evaluation by Kalman Filters, the model parameters estimation by a constrained recursive least-squares algorithm, and the detection criteria. The validation of the SmartID is performed on a test site in a smart grid located in Isernia (Molise, Italy). Experimental results show the good performance of the SmartID in the detection of both grid-connected and islanded operation; transitions from one condition to the other is only partially analyzed, due to the limitations introduced by the use of a commercial DG. The anti-islanding relay is the result of a joint research project among the University of Cassino and Southern Lazio, Ambra Energy System S.r.l. and Enel Distribuzione S.p.a.