协同多模接地控制的海洋核动力平台电网接地故障选线方法

Grounding fault line selection method coordinated with multi-mode grounding control for power grid of marine nuclear power platform

海洋核动力平台电网包含核反应堆敏感负荷,不同接地故障条件下均需要快速准确选线并切除故障线路。为避免某些高频频带下不同线路间零序电流分布差异不明显造成选线误判,提出基于被选频带零序能量的选线方法,并通过零序能量阈值判别高过渡电阻接地故障。发生高过渡电阻接地故障时,为避免电流互感器极性测量误差导致选线误判,协同多模接地控制将中性点切换至小电阻接地方式。此时,系统零序电压、健全线路零序电流幅值降低,故障线路零序电流幅值升高,基于此可预判故障线路;为避免互感器一次侧电气量过小造成较大的测量误差,利用切换前系统零序电压与切换后预判故障线路首端零序电流间的相位差构建就地化选线判据。仿真与动模试验结果证明,所提方法在不同故障场景下均能够准确选线,满足现场应用要求。

Power system of marine nuclear power platform contains sensitive loads of nuclear reactor,fast and accurate fault line selection and cutting methods are required under different grounding fault conditions.To avoid misjudgment of fault lines due to the insignificant difference of the zero-sequence current distribution between different lines under certain high-frequency bands,a line selection method based on zerosequence energy of SFB(Selected Frequency Band)is proposed.The zero-sequence energy threshold is used to identify grounding fault with high transition resistance.For grounding faults with high transition resistance,in order to avoid line selection misjudgment caused by current transformer polarity measurement errors,the neutral point is switched to low-resistance grounding mode coordinated with multi-mode grounding control.Then,the zero-sequence voltage of the system and the zero-sequence current of the healthy line decrease,while the zero-sequence current of the fault line increases,so the fault line can be predicted.To avoid the measurement error caused by the small amount of electricity in the primary side of transformers,the phase difference between the system’s zero-sequence voltage before switching and the predicted fault line’s zerosequence current after switching is used to construct the local line selection criterion.Results of simulation and dynamic model test show that the proposed method can correctly select the fault line in different fault conditions and meet the practical requirements of the field.