Abstract: In many analyzed events by WANO, operators relied solely on the reactor protection system to protect the reactor core without taking pre-emptive conservative actions. Especially during this off-normal grid conditions which was beyond the procedure guidance, these conditions may be further exacerbated by a reactor operator’s inexperience. In this paper, the potential adverse effects of the grid frequency change on PWR units operation is analyzed, the appropriate contingency plans are proposed so that the reactor operators can respond correctly in time when this off-normal grid condition occurs, to avoid causing reactor scrams to protect the reactor core, and the operators can conservatively monitor the PWR units operation, and a prudent margin to the plant safety limitations is always maintained.