A novel adaptive loss of excitation protection criterion based on steady-state stability limit

Among Loss-Of-Excitation (LOE) protections of synchronous generators, the impedance boundary criterion of steady-state stability limit (SSSL) is widely used to distinguish LOE from non-LOE conditions. But this criterion is sensitive to the variation of output active power of synchronous generator, and may mal-operate in external faults, power-swing and other non-LOE conditions. In this paper, a novel adaptive LOE protection criterion with an offset mho element based on SSSL is presented. The new criterion could automatically adapt to the system operating modes and correctly operate in LOE. Combine this criterion with some measures which prevent mal-operation in non-LOE conditions, a new LOE protection scheme is proposed. Simulation results demonstrated the effectiveness of the proposed adaptive LOE protection criterion and scheme.