中文摘要：

根据葛洲坝换流站一次双极停运事故的现象，指出过负荷保护误动作是这次事故的主要原因。为此通过比较改造前后过负荷保护实现方式的共同点和不同点，以交流滤波器技术规范中的试验数据为依据，推导了交流滤波器中丰富的谐波分量等效到基波热效应的表达式，并且分别给出了集成电路式和微机式交流滤波器过负荷保护中等效基波热效应电流的计算公式，据此说明改造后，微机式交流滤波器过负荷保护误动作的原因是生产厂家没有仔细考虑集成电路式保护的整定过程，机械地沿用原先的定值。给出了两种解决办法解决定值整定错误问题，可为以后更好地实施直流控制保护系统国产化改造提供参考。

英文摘要：

We analyzed an incipient fault after the completion of the home-produced Ge-Nan HVDC control and protection system. The fault trip of AC filter overload protection in Gezhouba converter station leaded to the out of service of all HP11/13 low-pass AC filters. The equivalent heat effects of harmonic currents on fundamental current, which were used in integrated circuit protection or modern microcomputer protection, were derived according to the data defined by the technical regulation of AC filter. The results show that the equivalent alternative resistance of AC filter is larger when the frequency of current gets higher because the eddy current loss and metal frame loss are larger with the higher current frequency. The reason of the accident is that the manufacturer adopts the original integrated circuit threshold of AC filter protection without considering the setting method for AC filter protection. The effect of low-pass filter used in A/D transition and equivalent heat effect of harmonic current were not implemented in microcomputer AC filter protection. By the comparison of modes , the AC filter overload protections before and after the home-produced Ge-Nan HVDC control and protection system were adopted, two corresponding methods were put forward focusing on the accurate computation of equivalent fundamental heat effect current of harmonic currents. When these methods are utilized in future China home-produced HVDC control and protection system, the HVDC can operate better.