A Fast Fault Protection Method for Power Transformers in Low‐Frequency Transmission Systems

In long‐distance grid‐connection scenarios, such as offshore low‐frequency transmission systems, the operating frequency of the power system is reduced. Under such conditions, conventional transformer protection methods that rely on steady‐state periodic quantities suffer from delayed response and criterion failure. To address the insufficient adaptability of transformer protection in low‐frequency transmission environments, this paper proposes a fast protection method for power transformers based on the generalized power reciprocity (GPR) characteristic. Based on Tellegen's quasi‐power theorem, a time‐domain GPR model of power transformers is established, and a GPR deviation index that is insensitive to system frequency variation is constructed as the internal fault criterion. In addition, a threshold‐setting principle based on hysteresis loss and rated capacity is proposed, enabling unified applicability for transformers with different frequency levels and rated capacities. Comprehensive verification through finite‐element simulations and dynamic model experiments demonstrates that the proposed method can achieve fast, stable, and reliable operation under various operating conditions and fault types. Compared with conventional protection schemes, the proposed approach exhibits higher sensitivity and stronger adaptability to low‐frequency operation, providing an effective technical solution for fast transformer protection in low‐frequency power systems.