Abstract: To address the issues of altered fault characteristics in distribution networks caused by high-proportion distributed generation (DG) integration, insufficient sensitivity of traditional directional overcurrent protection, and frequent maloperation, an adaptive harmonic impedance protection method for active distribution networks under wide-bandwidth measurement by electronic transformers is proposed. First, the wide-bandwidth transmission mechanism of electronic transformers is thoroughly analyzed, and a wide-band signal acquisition and spectrum correction model based on the Hanning window dual-line interpolation fast Fourier transform (FFT) is established, effectively suppressing spectrum leakage effects under non-synchronous sampling and noise interference. Second, by combining the equivalent circuit of active distribution network faults, the nonlinear influence mechanism of DG aiding current on measurement impedance is derived. A harmonic impedance trajectory tracking algorithm is proposed, along with a nonlinear protection setting correction strategy based on the Logistic function and a multi-criteria fusion logic, enabling real-time system state perception and dynamic setting optimization. Finally, a 10 kV typical distribution network simulation model verifies that this method achieves a protection operation accuracy rate of over 98.5% under complex conditions such as DG capacity fluctuations, frequency deviations, and high-resistance grounding, significantly enhancing the fault defense capability of active distribution networks.