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Sequence Impedance Parameter Estimation of a Three-Phase Transformer using Nonlinear Optimization Methods

Abstract:

This document presents the estimation of the positive, negative, and zero-sequence impedances of a three-phase, 50 kVA, 6300 - 231/133V transformer. Simulated short-circuit current measurements of single line-to-ground (SLG) and double line-to-ground (LLG) faults are fitted to their respective field measurements using non-linear optimization methods in MATLAB-Simulink. First, laboratory tests are performed on a laboratory-scale three-phase transformer using international standards to determine the sequence parameters. These values constitute the initial values to be used in the estimation stage. Subsequently, SLG and LLG short circuit events were performed where current data were recorded with the help of an oscilloscope. The recorded field data is compared against their simulated counterpart, generating two curves that overlap and have certain differences between them. To adjust the simulated curves with respect to the field measurements, the MATLAB-Simulink “Parameter Estimation” tool was used. This tool allows adjusting the sequence parameters of the model until the difference between the simulated and field values are minimized. Once the method was tested, the sequence parameters of the 50-kVA transformer were obtained following a similar procedure with the only difference that the high voltage side was fed with 500 V due to the physical conditions of the laboratory.