Unascertained rational number method applied to assess voltage sag in distribution system

Aiming at the uncertainty in the process of assessment voltage sag frequency in the distribution network (such as reliability parameters), combined with unascertained mathematics, this paper proposed an unascertained mathematics method to depict the uncertainty of the reliability parameters. Based on the traditional fault location method, a new unascertained mathematics assessment model and an approach were presented to assess the occurrence frequency due to voltage sags. This paper is focus on the uncertainties of the failure rate of system components in the process of assessment voltage sag frequency. The proposed method had been applied to the simple 9-node test system. Compared with the current deterministic and interval number methods, the simulation results have shown that this method is correct and usable, the existing point value evaluation method is a special case of the unascertained number evaluation method, the new methods provide more information.