Adaptability Analysis and Improvement of Traditional Transformer Protection in Offshore Low‐Frequency Wind Power System

ABSTRACT Since both ends of the AC transmission and outlet lines of the offshore low‐frequency transmission system are power electronic equipment, the current distortion during the fault process of the power grid may cause the adaptability of the existing protection to be reduced. The traditional ratiometric differential transformer protection method based on the second harmonic braking principle has a serious delay problem when the low‐frequency operation system fails. How to improve the existing protection performance and solve the problem of protection adaptability under the offshore low‐frequency wind power system is the core problem of this paper. In this paper, a zero‐sequence differential protection based on phase difference is proposed for the internal grounding fault of the transformer, which has strong anti‐excitation inrush current interference, and the protection criterion is the self‐generated zero‐sequence current and the neutral point zero‐sequence current on the high‐voltage side of the transformer. However, since there is no zero sequence current in the case of interphase fault, a transformer protection based on the phase difference of the negative sequence current is proposed. The offshore low‐frequency wind power transmission system was built by PSCAD, and the feasibility of the protection algorithm was verified by MATLAB. The simulation results show that the proposed protection principle operates quickly and reliably no matter any fault occurs in the low‐frequency transformer.