Voltage Sag State Estimation For Power Distribution Systems Using Kalman Filter

The increased awareness on power quality has resulted in the need to quantify the voltage sag performance of a distribution feeder, similar to what has been done on characterizing the reliability performance of a feeder. Since it is impossible to measure the sag level at every node of a distribution feeder, estimation of sag characteristics at unmetered nodes becomes necessary. This paper proposes the concept of "voltage sag state estimation" using a Kalman filter. The applied technique has the following characteristics: 1)It makes use of the model characteristics of a distribution feeder, 2) It is based on a limited number of metering points, and 3) It employs a Kalman filter to estimate the sag profile along a distribution line. The procedure is then applied to part of an IEEE 123 bus distribution test system and the results have been compared with least mean square approach. The comparison shows the improvements provided by this method. The results of the sag state estimator can then be used to calculate the feeder power quality performance indices such as the System Average RMS Frequency Index (SARFIx).