This study proposes a method for determining the equivalent circuit constants of synchronous machines. First, a new approach to calculate the equivalent circuit constants considering mutual leakage reactance between field and damper windings is proposed. This method can determine the constants by substituting synchronous machine constants (time constants and reactances) in simple formulae. As these machine constants are easily obtained from the frequency characteristics of the d-axis and q-axis operational impedances measured through the standstill DC test, determining the equivalent circuit constants is considerably simplified. Second, an improved DC test that can measure the operational impedances of a synchronous machine with a brushless excitation system is proposed. This method allows for performing the DC test without separating the diode rectifier circuit from the field winding of a rotor. As a practical example, the proposed method is implemented on a 10-kW salient-pole synchronous generator with an external diode bridge rectifier connected to field winding terminals. Using the determined equivalent circuit constants, the field and armature transient currents at a sudden three-phase short circuit are simulated. By comparing the simulation results with measurement test data, the validity of the proposed method is verified.
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