Improvement of the impedance-based loss-of-field protection scheme based on the dynamic behavior of the synchronous generators

This paper deals with an innovative Loss of Field Protection Scheme (LoFPS), in which, some key supplementary features are provided to avoid spurious trip of the Conventional Impedance-Based Relay (CIBR) during Stable Power Swing (SPS). The proposed algorithm is developed for two conditions of the multiple-parallel-synchronous generator (SG) and single-SG in service. Entrance time (t(i)) of Z-trajectory to the CIBR zones is utilized for single-SG in service owing to the different dynamic responses of the SG to the LoF/SPS events. Meanwhile, for the multiple-parallel-SGs condition, the average value of the variation of the output reactive current of SG (delta I-RSG) is selected to analyze the dynamic behavior of the faulty-and healthy-parallel-SGs. The delta I-RSG for all the parallel-SGs during both normal and SPS conditions has a similar polarity, whereas during LoF incidence in one SG, its polarity is different for the faulty and healthy-parallel SGs. Therefore, the nuisance trip of the CIBR can be easily avoided by implementing the selected features. Widespread simulation studies in MATLAB/Simulink environment on the IEEE 9-bus test system affirm the superiority, higher reliability, and easy implementation of the developed LoFPS than other schemes, especially the CIBR ones.