Determination of Synchronous Machine Parameters Using Standstill Frequency Response Tests at Different Excitation Levels

The standstill frequency response (SSFR) experiment is a well-proved test procedure to extract synchronous machine parameters using a low-level excitation signal. Model parameters extracted from SSFR are assumed to be completely linear due to the small excitation level and incursion on the saturation curve. This research is concerned with the low-level region of the saturation curve, where SSFR tests are applied, and the effects of the B-H curve excitations on the estimated model parameters; application of different levels of sinusoidal excitation signal allows moving into different positions on the B-H curve. To analyze the response signals from the SSFR tests, the test is carried out while the machine is at standstill and the d-axis armature winding is excited with a sweep of sinusoids of constant voltage considering the field winding in open and short-circuit. Signal responses are processed using the Fourier transform to extract information of magnitude and phase angle. Three transfer functions are required to characterize the d-axis because it is a two-port network, whereas in the q-axis, only one transfer function is needed. Different order models were characterized. The estimated parameters demonstrate that their behavior is related to the non-linear low-level saturation-curve of the synchronous machine. Tests were performed on a 7 kVA, 220 V, 60 Hz salient-pole synchronous generator.