A severity assessment method for multiple voltage sag

To evaluate the influence of voltage sag on electric-equipment and guide the design of compensation scheme for voltage sag, we need to evaluate the severity of effect of voltage sag on loads. This paper analyses the agglomeration effects of multiple voltage sag on the time scale. For irregular multiple voltage sag, this paper converts its voltage time-series curve into voltage duration curve, and defines its average over-limit duration time difference and over-limit probability. Then, this paper builds a more elaborate improved voltage sag severity index by superposition of the sensitivity of multiple duration intervals which voltage sag goes through. Combining the improved voltage sag severity index and voltage duration curve, this paper establishes an evaluation method for multiple voltage sag severity. According the analysis on test data of IEEE 1159.2, the correctness of the proposed scheme is validated.