MMC-HVDC 换流变压器复杂性涌流产生机理及其影响分析

Analysis on Generation Mechanism and Influence of Complex Inrush Current in MMC-HVDC Converter Transformer

柔性直流输电系统中换流变压器阀侧发生单相接地故障后,工程中采取先跳阀侧断路器再跳网侧断路器的方式,在此过程将先后诱发故障性涌流及恢复性涌流(称为复杂性涌流)。文中从磁链变化的角度分析并推导了复杂性涌流的产生机理。当换流变压器阀侧发生单相接地故障后,阀侧直流分量持续流向换流变压器而导致铁芯饱和,产生故障性涌流;之后保护将跳开阀侧断路器,由于故障性涌流阶段的磁链积累,铁芯中含有大量剩磁并在阀侧断路器跳开后产生恢复性涌流,从而导致复杂性涌流现象。复杂性涌流中含有大量谐波,在一定条件下会通过交流线路传播放大并导致线路末端产生谐波过电压,文中对此进行了讨论并给出了一种复杂性涌流抑制方案。最后,参考实际柔性直流工程中的断路器配置,利用PSCAD/EMTDC仿真验证了理论分析的正确性。

After a single-phase grounding fault occurs on the valve side of the converter transformer in the flexible DC transmission system,the method of tripping the valve-side circuit breaker first and then the grid-side circuit breaker is adopted in engineering.In this process,the fault inrush current and the recovery inrush current(called complex inrush current)will be induced successively.The generation mechanism of complex inrush current is analyzed and deduced from the perspective of flux change.When a singlephase grounding fault occurs on the valve-side of the converter transformer,the DC component on the valve-side continuously flows to the converter transformer,resulting in the iron core saturation and fault inrush current.After that,the protection will trip the valve-side circuit breaker.Due to the flux accumulation in the fault inrush current phase,the iron core contains a large amount of residual magnetism and generates recovery inrush current after the valve-side circuit breaker trips,which leads to complex inrush current phenomena.The complex inrush current contains a lot of harmonics,which will propagate and be amplified through AC lines under certain conditions and lead to the harmonic over-voltage at the end of the line.This paper discusses this and gives a scheme to suppress the complex inrush current.Finally,referring to the configuration of circuit breakers in the actual flexible DC project,the correctness of the theoretical analysis is verified by PSCAD/EMTDC simulation.