When electric faults take place in onsite power system of nuclear power plants, the voltage of safety related bus can be affected, as a form of voltage sag, by electrical transients. The safety related buses in nuclear power plants have a role of power supplying to essential loads for safety shutdown of reactor. If voltage sag of the safety related bus would be occurred and impact on the operating characteristics of motor would be existed, the risk of nuclear power plants will be increased. Therefore, it is important to analyze the effect on voltage sag of safety related bus and operating characteristics of motor due to electrical transients in nuclear power plants. This study performed that the phenomenon of voltage sag and the effect on motor operation by various electrical transients are simulated and analyzed.