The 4-generators, two-areas, system is proposed in  P. Kundur, Power System Stability and Control, McGraw Hill, 1994. This test system is well-suited for the study of concepts related to the different nature of local and inter-area modes. Folder 1 contains the original case. Folders 2 and 3 includes test cases with PSSs without and with phase compensation tuning, respectively.
Download the Four Generator System Case.
 Prabha Kundur. Power System Stability and Control. McGraw-Hill Professional, 1994.