Patent ID: 7630794

Claim:
An isolated operation detecting method for detecting whether a distributed power supply is cut off from a power system and isolatedly operated or not on the basis of a power fluctuation injected into the power system, comprising: a first step that injects a power fluctuation into the power system; a second step that measures a system cycles; a third step that adjusts the injection of the power fluctuation so that the system cycles increase when the system cycles are found increased than the previous system cycles as a result of the measuring, and decreases when the system cycles are found decreased than the previous system cycles as a result of the measuring; a fourth step that produces a change pattern of a plurality of latest system cycles based on a plurality of deviations of the plurality of latest system cycles from a fixed number of past previous system cycles by calculating whether each of the deviations between each of the plurality of latest system cycles and each of the fixed number of past previous system cycles exceeds a corresponding one of a plurality of threshold values set for each deviation, and forming the change pattern based on the result of this calculation, and forms an isolated operation determination area from each of the threshold values set corresponding to each of the plurality of latest system cycles; and a fifth step that determines an isolated operation on the basis of the change pattern by judging whether the change pattern formed from the plurality of deviations is within the isolated operation determination area.