Semi-analytical method for determining d-axis synchronous generator parameters using the dc step voltage test

The DC step voltage experiment is an alternative and non-destructive time-domain test to extract parameters from electrical machines that follows the standstill frequency response test procedure described in IEEE standard 115A. This work presents a new method for semi-analytically determining the characteristic parameters of the d-axis synchronous machine model. The test is carried out when the machine is at rest and the rotor´s position is at d-axis; a DC-controlled power source is applied suddenly at two of the three terminals of the stator machine and the field circuit is short-circuited. Test measurements of d-axis stator voltage excitation and field and d-axis stator current responses were used. Both stator and field current patterns are simultaneously fitted to exponential functions which coefficients are analytically related to the d-axis characteristic parameters of the equivalent circuit. These characteristic parameters come from the conventional two transfer functions: direct-axis operational inductance L_d(s) and the armature to field transfer function sG(s). To validate the proposed methodology, test data is used in the d-axis parameter determination of a 7 kVA, 220 V, 60 Hz synchronous generator