Indices of Intermittence to Improve the Forecasting of the Voltage Sags Measured in Real Systems

This paper provides a means of forecasting the future average performance a regional electric power system in terms of sags per year based on data accumulated over a four-year period. The paper also presents statistical analyses of the measured data. The sags measured in real systems consist of both rare voltage sags and grouped voltage sags (clusters); clusters are stochastic events that must be detected and removed to allow the estimation of the future performance based on a Poisson process. To detect and remove the clusters, new site indices of intermittence are proposed. These indices were measured in every site at which clusters were present, and the measurements included the frequency, time of grouping, and the large number of sags that constituted them. The performance of the forecast was evaluated by comparing the results obtained using the proposed indices with the results derived using a time filter equal for every site. The results showed that the forecast of the rare voltage using a few years' worth of field data had acceptable errors and was not prohibitive. The main aspect, which must be investigated further, is related to the choice of the best threshold on the intermittence site indices.