Abstract: Partial discharge monitoring is crucial for the safe and stable operation of power transformers. The development of non-invasive monitoring methods applicable to both offline and online scenarios can significantly enhance operational safety. We investigated the mechanism of high-frequency signal detection by current transformers (bushing TAs, also referred to as bushing CTs in engineering practice) installed in bushing risers through modeling, and verified the feasibility of internal transformer partial discharge monitoring by using bushing TAs. Tests were conducted on 11 bushing TAs installed on a 500 kV transformer to evaluate parameters such as transfer impedance, waveform distortion rate, and linearity. Results confirmed that the bushing TAs met relevant standards and could function effectively as high-frequency current sensors. During breakdown tests on a full-scale 500 kV transformer, partial discharge signals were successfully captured by using bushing TA-connected detection equipment. The acquired signals demonstrated consistent trends and strong linear correlation (correlation coefficient > 0.91) with measurements from bushing taps and core clamp grounding points. Notably, the signal-to-noise ratio of bushing TA measurements exceeded that of core-grounding HFCT by 3.86 times and surpassed bushing-tap HFCT by 2.60 times. These findings validate both the feasibility and accuracy of implementing bushing TA-based monitoring for internal transformer partial discharges.