Practical Improvements to Generator Parameter Validation Using Stator-Decrement Test

This article discusses the accuracy issue in applying the commonly used stator-decrement test (load rejection) method for validating generator d-axis parameters. Theoretical analysis and actual examples are provided to illustrate how the accuracy issue is related to the rotor field winding current as well as hysteresis, which has not been analyzed in detail for the second-order generator models widely used in power system studies. A generic, practical method for validating generator synchronous inductance is proposed and proven with actual field measurements and model validation study results using the GENQEC model. The generator field current compensation factor of the GENQEC model improves the field current accuracy independently of magnetic saturation. Its advantages are demonstrated in model parameter validation using field measurement results from in-service salient-pole and round-rotor synchronous generators. The proposed method with the GENQEC dynamic model can be used to establish a baseline for accurately validating generator direct-axis parameters using stator-decrement test results. The innovative method of validating generator synchronous d-axis reactance proposed in this article can be a practical and reliable alternative to the test methods provided by IEEE standards.