Long term monitoring of voltage sags at 6.6 kV distribution substation

The paper presents the power quality monitoring results at a 6.6 kV distribution substation. The long term monitoring was performed during a year from October 1998 to November 1999 in order to evaluate the power quality of the 6.6 kV distribution system. Three-phase voltages and line currents were measured continuously at the site during the year. Whenever voltage sags were detected, the measured results were stored on the hard disk on a personal computer based data acquisition system. In this study, the harmonic distortions have also been investigated for the power quality evaluation and also for the identification of the causes of voltage sags. The effect of the load unbalance, i.e., one of the other factors of power quality, has also been investigated in this paper