Characteristics of voltage relays for embedded synchronous generators protection

Here, a comprehensive characterisation of the performance of voltage relays, focusing on their capability to detect islanding of embedded synchronous generators is presented. Such characterisation is done by using the performance curves and the concept of critical reactive power imbalance, which allows a systematic analysis of voltage relays considering a wide range of system operating points. The impacts of important factors on the relay performance are evaluated, such as the presence of voltage-dependent loads and the generator exciter control mode. Moreover, a graphical approach that allows protection engineers to adjust voltage relays to reach two objectives simultaneously: (i) to be sensitive enough to detect islanding efficiently and (ii) to satisfy the protection requirements against abnormal voltage variation is proposed. Results can be quite attractive to understand voltage relays behaviour and limitations and thus, they can be adjusted more efficiently