Abstract: For an isolated power station abroad with 20 gas turbine generator sets each of 25MW, totaling an installed capacity of 500MW, when the generator sets experienced low voltage and low frequency, the protection device did not trip the preset line outlet switch according to its established tripping outlet action logic and tripping outlet setting value, resulting in abnormal action information. The reasons why the protection device did not operate according to the set value when the generator set was operating under low - voltage and low - frequency conditions were identified, analyzed and dealt with, so that it could continue to ensure the safe and stable operation of the generator set, laying a solid foundation for the handling of similar faults and the optimized management of protection devices in the future.