Modelling and Quantification Methods of Voltage Sags and Voltage Unbalanced

First, the features of various power quality disruptions (PQDs) and their standard have been discussed in brief to reveal the most important PQDs. Further, based on huge economic impacts and frequency of occurrences, the modellings and quantification methods of voltage sags and voltage unbalanced have been incorporated to highlight their shortfalls. The R.M.S voltage method of voltage sag characterization is modelled and it is shown that this method provides overestimation in voltage sag duration as well as dependent on the window length of the samples. Also, the model is developed to show the impacts of fault resistance and transformer winding connections on the characteristics of voltage sags. Finally, the quantitative descriptions of degree of voltage unbalanced, namely voltage unbalance factor (VUF) has been presented. It is shown that the degree of voltage unbalanced (VUF) is not sufficient for the accurate prediction of the impacts but condition of unbalanced is also desirable for the accurate assessment of the impacts of the voltage unbalanced.