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通过对主冷却剂泵(RCP)低频保护判据的分析发现，低频判据采用相电压U_a，低电压闭锁采用线电压 U_(ab)，是造成 RCP 低频保护误动的根本原因，进而引起了停机停堆。因为当6kV 变压器 A 相发生单相接地故障时，U_a 降低，测频通道检测到频率低，但基本不变，低电压闭锁不能检测到电压低，从而开放低频保护逻辑。针对低频保护判据存在的缺陷，提出将测频和低电压闭锁的电压量都采用线电压，并取自同一 U/V 变换器的改进措施，改进后防止了低频保护误动，提高了可靠性。
Based on the analysis of the low frequency protection criterion of the main coolant pump (RCP), it is found that the phase voltage U_a is used in the low frequency criterion and the line voltage U_ (ab) is used in the low voltage blocking. This is the root cause of the low frequency protection of RCP. Shutdown shutdown. Because when 6kV transformer A phase single-phase ground fault, U_a lower frequency channel detected low frequency, but basically the same, low-voltage lock can not detect the low voltage, thus opening the low-frequency protection logic. Aiming at the shortcomings of the low frequency protection criterion, this paper proposes that both the frequency measurement and the low voltage blocking voltage should adopt the line voltage and be taken from the same U / V converter. After the improvement, the malfunction of the low frequency protection is prevented and the reliability is improved Sex.