Research On Voltage Sag Characteristics And The Assessment Of Its Influence On Sensitive Equipment

The paper researched the characteristics of voltage sag and the assessment of its influence on sensitive equipment. Voltage sags are classified and analyzed for a thorough understanding of it. Characteristic indexes that can characterize the waveform of pre-event segment, transition segment and during-segment respectively are studied based on a statistical analysis of the measured waveform. The distribution characteristics and scopes of the five characteristic indexes are proposed and the propagation characteristics of phase jump are studied.The traditional description method of voltage sag is introduced first, and then its limitations applying in sensitive equipment immunity assessment process are analyzed. A new voltage sag description method using multiple voltage threshold and duration is presented combining with the equipment voltage tolerance curve. On this basis the single event and site assessment method for equipment immunity evaluation and voltage sag severity index is proposed. The proposed method can be used to obtain the failure frequency and frequency range of equipment conveniently. Besides, it can solve the overestimated and imprecise problems of the traditional method. Finally, we used the proposed method to assess the immunity of four typical sensitive equipment, PLC, ASD, AC Relay and PC. The results obtained from the traditional methods were compared and analyzed. The overestimations of traditional method as well as the feasibility of the proposed method are verified.