Effect of field voltage source impedance on load rejection test results of large rating synchronous generators

Summary form only given. This paper presents a technique to determine the effect of the field voltage circuit during the load rejection test of a large rating salient pole synchronous generator. Once the circuit powered by a six-pulse converter connected to the excitation transformer of the generator unit corresponds to a power supply voltage not constant immediately after the load rejection, a careful evaluation of the resulting signals is necessary to extract rotor and stator parameters from the comparison with theoretical expressions derived under the assumption of constant field terminal voltage and excluding external effects. The results obtained in the load rejection test of a 179 MVA, 13.8 kV generating unit at Nova Ponte Power Plant show the parameters that are more affected by the external impedance in series with the rotor circuit and how to compensate them.