Abstract-The method presented in this paper addresses the problem of voltage sag state estimation (VSSE). The problem consists in estimating the voltage sags frequency at non-monitored buses from the number of sags measured at monitored sites. Usually, due to limitations on the number of available voltage sag monitors, this is an underdetermined problem. In this approach, the mathematical formulation presented is based on the fault positions concept and is solved by means of the Singular Value Decomposition (SVD) technique. The proposed estimation method has been validated by using the IEEE 118 test system and the results obtained have been very satisfactory.Index Terms-voltage sags (dips), power quality monitoring, power system, Power Quality.
I. INTRODUCTIONOLTAGE sags (also known as voltage dips) are a frequent power quality disturbance that can cause failure or malfunctioning to very common devices used in industrial and tertiary sectors. This disturbance, as with other power quality problems, must be approached from a compatibility point of view that requires characterizing the equipment sensitivity as well as the power system behavior. This paper relies on this second aspect.In order to describe the voltage sags performance in the power system, a method must be established that can provide representative values of the expected number and characteristics of voltage sags at system buses. To quantify the system behavior, a great emphasis has been placed recently on the use of different quality indices. Some of these indices are defined at a site level (for a specific point of the supply system), but there are others defined at a system level (for the whole system) [1]- [4]. For assessing site indices, monitoring the power supply at the site of interest can directly provide the information to evaluate the index. However, in order to calculate voltage sag indices of the whole system, ideally the monitoring of all sites should be required. Clearly, such a monitoring program is not economically justifiable.This work has been financed by the Ministerio de Ciencia e Innovación (MICINN), Spain, under project ENE2010-17459 (CON) A. Hernández, R. M. de Castro and M. Izzeddine are with the