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As smart grid applications, distributed generation, and microgrid technologies have become more widespread, new safety-related issues have arisen. Unintentional islanding is an example of a grid fault that may result in damage to electrical equipment and severe personal injuries. In this paper, an antiislanding system employing power line communication (PLC) and direct-sequence spread spectrum (DSSS) modulation implemented with software-defined radios for continuous signaling is tested in a laboratory test setup. A concept of a fault detection algorithm is evaluated. A DSSS sensitivity analysis is carried out to investigate system's performance against variation of a signalto-noise ratio, and define optimal DSSS settings. The results of the analysis are interpreted, and conclusions are drawn. A transformer bypassing scheme allowing to increase the fault detection speed and throughput is introduced and tested, and the conditions of applicability are described. As a result of the study, recommendations for the system development are presented.

Loss-of-mains (LoM) protection is crucial in modern smart grids (SGs), where the number of distributed generation (DG) units has increased making the grids more complex. An LoM situation means that the DG unit(s) is/are still supplying the grid while the connection to the supplying electric power distribution grid is off. This can cause fatal injuries to humans and damages to the equipment. A power line communication (PLC) based LoM concept is introduced, where continuous signaling is used as an indication for the LoM protection from the primary substation through the MV grid, the MV/LV transformers, and each low-voltage (LV) grid to the customers. However, the MV/LV transformers constitute a barrier for the PLC. Thus, in this paper, the channel characteristics and modeling of the MV/LV transformer as a function of frequency in the frequency band from 100 Hz to 1 MHz is analyzed. A model for the transformer is compiled and verified by input impedance measurements.