Analysis of gray Box Modelling of Transformers

Abstract

Calculation of power system transients involving transformers require models that incorporate capacitive behavior. The paper outlines how classical low-frequency transformer models can be extended with capacitances and how to fit the parameters based on typical values, test report and frequency response measurements. Justified tuning factors are proposed. The responses of the models are compared to measurements in frequency domain, and with detailed black-box models in studies of transient recovery voltage and lightning. The models show reasonable agreement including the first resonance point, but with too low damping without proper adjustments.