Optimization algorithm for transformer admittance curves

The topic of this digest is related to the broadband equivalent circuit modeling of transformers. The measured frequency response of a three-phase transformer is replicated with equivalent circuits consisting of RLC networks. To determine the values of the RLC parameters, rational function representations for the necessary admittance curves are found. The RLC values are extracted from the rational functions. This digest describes an algorithm directed towards simultaneously approximating the real and imaginary parts of a transformer admittance curve with rational functions. It discusses the conditions to be fulfilled for the algorithm to give satisfactory results and the general strategy behind the algorithm.