*5.1. Test System*

The proposed method is testified on the modified IEEE 39-bus system. The base power of the system is 100 MW, and the system is divided into the source (Area I) and sink (Area II) areas by four tie-lines 1–39, 2–3, 3–18, and 16–17, as shown in Figure 2. Two wind farms with a total capacity of 500 MW are connected to buses 17 and 21. As shown in Section 3.1, TSI calculated by power angle is adopted to quantify TS margin. So, this paper assumes that the wind farms have sufficient reactive power reserves and low voltage ride-through capability to ensure they do not trip. A three-phase short circuit on each tie-line is pre-selected as the contingencies.
