Application analysis of large hydro-generator loss of excitation protection and its improvement

Concerned with loss of excitation (LOE) protection for large hydro-generators, several engineering issues with their improvement approaches are investigated. Based on the analysis of the variable excitation voltage criterion on its principle, performance and application, it´s indicated that the expected function advantages of the criterion are actually not available, bringing about more potential failure in the rotor circuit instead. As a result, it´s recommended LOE protection scheme for large hydro-generators should mainly consists of criteria on the stator side. The setting values of LOE protection and under excitation limit (UEL) control are calculated separately, resulting in the mismatch of each other easily, which impairs the generator´s power supply support. Considering the steady state stability impedance criterion commonly used for large hydro-generator LOE protection as principal criterion, the paper presents an algorithm of comparing the operation zone of LOE protection and UEL control, followed by several schemes on their better cooperation.