Long-term voltage collapse analysis on a reduced order nordic system model

This paper analyzes and explains the mechanism behind long-term voltage collapse in the NORDIC32 test system. For this purpose a simplified test system called N5area, reflecting the key voltage collapse characteristics of NORDIC32 is proposed. Applying control algorithms is much easier in N5area than in NORDIC32. Load recovery and generator excitation current limiter actions which are two important factors contributing to long-term voltage collapse are considered. Dynamic simulation results for a specified long-term voltage instability scenario are explained and discussed. The effect of generator current limiters is analyzed using PV curves. Furthermore, two different control strategies for controlling the shunt capacitors are applied as countermeasures to save the system. The two strategies are explained and compared and it is shown that control using the voltage at neighboring buses gives better performance.