Excitation System Output Quantities-Based Loss of Excitation Detection in Synchronous Generators

In the earliest generation of loss of excitation (LOE) protection relays, the exciter’s output voltage ( $V_{e}$ ) or output current ( $I_{e}$ ) were employed for the LOE protection of synchronous generators (SGs) by employing under-voltage or under-current schemes. This paper explores using the excitation system’s output quantities ( $V_{e}$ and $I_{e}$ ) to detect the LOE phenomenon in SGs. The phase domain (PD) model of SGs available in the real-time digital simulator (RTDS) is used in this paper rather than the well-known dq representation, because only the PD model can provide realistic modeling of the LOE phenomenon based on the IEEE Standard C37-102, and $V_{e}$ and $I_{e}$ measurements. A new combined scheme using $V_{e}$ and $I_{e}$ is proposed for the LOE protection as an LOE failure causes an interruption on $V_{e}$ or $I_{e}$ . Through simple paralleled under-voltage and under-current logics, such interruptions can be easily detected. The proposed method is compared with conventional impedance-based schemes through case studies, including the complete LOE (CLOE) and partial LOE (PLOE) failures, and the stable power swing (PS) phenomenon, showing superior performance by reliably detecting CLOE events and maintaining secure operations during PS events, although it may perform unreliably during PLOE events.