海上风电交流电缆空充谐振事故分析及应对方案

Analysis of a resonance accident from the no-load closing of AC cable in an offshore wind farm and corresponding countermeasures

相同条件下高压交流海缆对地电容是架空线路的20倍以上,在海缆空充时容易出现谐振现象。针对一起海上风电500 kV交流海缆空充过程中出现谐振并引起线路差动保护误动的事故,分析故障录波数据,根据电路理论分析海缆空充过程中的谐振机理,并通过仿真验证指出事故原因为:长距离高压交流海缆接入弱系统导致海缆空充过程出现低于1.5倍工频、高幅值的谐振过电流,经保护装置电流补偿后仍存在较大容性谐振差流,造成差动保护误动。结合工程情况,提出优化保护装置电流二次回路接线、根据系统工况和线路电容电流大小动态调整差流动作门槛的应对方案。最后,通过RTDS闭环测试验证了所提方案的有效性。

Under the same conditions,the ground capacitance of high-voltage AC submarine cables is over 20 times greater than that of overhead lines,making resonance phenomena more likely during no-load closing of submarine cables.This paper addresses an incident during the no-load closing of a 500 kV AC submarine cable in an offshore wind farm,where resonance caused a malfunction of the line differential protection.The paper analyzes the fault re⁃cording data and investigates the resonance mechanism during the closing process based on circuit theory.Simulation results indicate that the incident was caused by the integration of long-distance high-voltage AC cables into a weak system,leading to resonance overcurrents that were below 1.5 times the power frequency but of high magnitude.De⁃spite current compensation from the protection device,significant capacitive resonant differential currents remained,resulting in the malfunction of the differential protection.In light of the engineering context,the paper proposes a re⁃sponse strategy that optimizes the wiring of the secondary circuit of the protection device and dynamically adjusts the threshold for differential current action based on system conditions and the magnitude of line capacitive currents.Fi⁃nally,the effectiveness of the proposed countermeasures is validated through RTDS closed-loop testing.