This study presents a new index for fast and reliable protection of the synchronous generator (SG) against loss of field (LOF) incidence, focusing on the operation time, reliability in clustering LOF, power system disturbance (PSD), and practical application. To this end, all allowable electrical parameters at SG output are acquired and thoroughly analysed. Analytical analysis of the parameters indicates that reactive power (Q SG) and load angle (δ SG) parameters have better conditions to improve the mentioned factors. Hence, based on the δ SG increment and Q SG decrement during LOF events, a new index based on the ratio of deviations of the δ SG over Q SG (Δδ SG /ΔQ SG) is proposed as a suitable criterion owing to remarkable fast sensitivity to LOF and PSD events. In the proposed algorithm, analysis of the events by the proposed Δδ SG /ΔQ SG index is dependent on ΔV SG < 0 condition. Extensive simulation studies demonstrated that the proposed LOFPS is a straightforward method to immediately and securely distinguish between LOF and PSD events, and it also has minimum operation time than other methods. Moreover, numerical data affirmed the greater changes of the Δδ SG /ΔQ SG index during LOF events than those in PSD events, giving rise to the easy clustering of both LOF/PSD events.
