Surge tests were performed to derive a generator model considering its frequency characteristics. Impulse voltages were applied to one terminal of the generators after placing a variable capacitor at the same terminal. The inductances and the core-loss resistances of a generator model can be determined from the measured oscillating voltages. This paper presents a generalization of the method aimed at deriving these generator parameters. The accuracy of the proposed method is confirmed to be satisfactory after comparing measured and simulated transfer voltages.