Effect of distribution system protection on voltage sags

The general relationship between distribution system protection schemes and voltage sags is presented. The definition, characteristics, and sources of sags are given. The probability of sag occurrence is studied from the three points of view: reliability assessment, historic reliability, and general tendency. General values for the reliability assessment uncertainties and facts related to the historic reliability are proposed. The general tendency is analyzed in normalized form. The reliability index appropriate for the study of the protection scheme interaction with voltage sag are described.