电流差动保护在海上风电低频送出线路中的适应性分析

Adaptability Analysis of Current Differential Protection in Low-frequency Transmission Lines of Offshore Wind Power

低频输电技术在中远距离海上风电领域应用潜力巨大。电流差动保护是广泛应用的传统交流保护,面对电力电子型电源时其性能可能受到影响,故有必要研究其在海上风电低频输电系统中的适应性。文中基于故障复合序网推导了直驱风机和模块化多电平矩阵换流器的电源特性对故障电流的影响,理论分析了电流差动保护的适应性。为定量分析保护适应性,提出了基于改进节点方程的故障电气量计算方法,计算给定故障条件下的故障电流和保护判据取值,判断保护动作情况。研究表明,单相接地和两相短路时保护灵敏度降低,甚至可能拒动;两相接地和三相短路时,保护能正常动作。最后,建立PSCAD/EMTDC仿真模型验证了理论分析和计算方法的正确性。

Low-frequency transmission technology has enormous potential for application in the field of medium-and long-distance offshore wind power.Current differential protection is a widely used traditional AC protection,and its performance may be impacted when facing power electronic power sources.Therefore,it is necessary to study its adaptability in offshore wind power low-frequency transmission systems.The paper derives the influence of source characteristics of permanent magnet synchronous generators and modular multilevel matrix converters on fault current based on fault composite sequence networks,and theoretically analyzes the adaptability of current differential protection.To quantitatively analyze the adaptability of protection,a fault electrical quantity calculation method based on improved node equation is proposed,which calculates the fault current and protection criterion values under given fault conditions,and judges the protection operation situation.Research shows that the sensitivity of protection decreases and may even fail to operate during single-phase-to-ground and two-phase short-circuit faults.The protection can operate normally under two-phase-to-ground and three-phase short-circuit faults.Finally,a PSCAD/EMTDC simulation model is established to verify the correctness of the theoretical analysis and calculation methods.