As one of the core components of the power system, the reliability of the power transformer directly affects the safety and stability of the entire system. Winding deformation is among the most common faults in transformers, and its effective detection is a critical task in practical engineering. The frequency response method has become the most widely accepted approach for detecting transformer winding deformation due to its accuracy, simplicity, cost-effectiveness, reliability, and non-destructive nature. However, the frequency response characteristics of transformer windings are also influenced by factors such as bushings, transformer oil, and wiring configurations. To investigate the actual impact of each component, this paper uses a 220 kV three-phase three-winding power transformer to conduct comparative tests both with and without bushings and transformer oil, as well as tests involving different wiring arrangements. The results indicate that, even in the absence of winding faults, components such as bushings, insulating oil, and tap changers can significantly affect the frequency response curve, potentially leading to inconsistent diagnostic outcomes.