This paper presents the analysis and modeling of the non-minimum phase effects that can occur in the low-frequency response of transformers. This effect is highlighted when the phase response has angles outside the range -90° to +90° and the typical response shape, which consists of two resonance points for the lateral phases and one for the central phase, is not found. Analysis based on physical effects, particularly the grounding capacitances and their association with the response, is presented. A model is proposed for characterizing and reproducing transformer low-frequency response, including the non-minimum phase effect. Actual frequency response measurements were obtained experimentally to assess the modeling.