Determining accurate area of vulnerability for reliable voltage sag assessment considering wind turbine ride-through capability

Abstract

The accurate calculation of area of vulnerability (AOV) and expected sag frequency (ESF), which in turn leads to reliable assessment of voltage sag performance, is very useful in establishing efficient planning for the mitigation of voltage sags at buses where sensitive equipment are installed. This paper proposes a method for accurate determination of AOV for fault induced voltage sags. To do so, different mathematical solvers are used to solve the residual voltage equations in order to find the accurate critical points on lines partially included in AOV. Moreover, a new iteration-based technique is developed to calculate ESF with high degree of accuracy considering low voltage ride-through requirement for wind turbines. The proposed technique can efficiently and accurately assess voltage sag performance at wind turbine connection points and provides reliable long-term performance evaluation of tendency and degree of voltage sag occurrences expected to cause wind turbine disconnection. The proposed method is applied on IEEE 30-bus test system penetrated with eight wind turbines and a practical network of Iran equipped with sensitive loads.