适用于海上风电低频变压器的保护方法研究

To address ihe issue of waveform distortion in differential currents of transformers within flexible low-frequency transmission systems leading to the failure of traditional second harmonic restraint principles, a novel protection method for low-frequency transformers based on empirical mode decomposition (EMD) and time-domain projection area is proposed. This method first uses EMD lo adaptively decompose ihe differential current into a series of intrinsic mode functions (IMFs) and a residual component. Subsequently, the time-domain projection area of each IMF component is calculated lo construct fault identification features. Based on theoretical analysis, threshold criteria are set to accurately distinguish between magnetizing inrush currents and internal fault currents. A simulation model of an offshore wind power flexible low-frequency transmission system was established using PSCAD/EMTDC for validation. The results show that the proposed method can achieve accurate identification within 60 ms after a fault occurs, demonstrating significantly higher reliability compared to traditional methods. No misjudgment occurs under various interference conditions, including different closing angles from 0° to 90°, typical harmonic distortion rates of 3%9 5%, and 7%, and Gaussian white noise with signal-to-noise ratios of 20, 25, and 30 dB. The proposed method effectively overcomes the shortcomings of traditional approaches, exhibits strong robustness, and provides a feasible solution for transformer protection in offshore low-frequency transmission systems.