直流输电系统利用大地回线自动转为金属回线抑制直流偏磁策略研究

摘要

直流系统接地极流过较大电流是导致中性点接地变压器中流过直流电流、引发直流偏磁的主要原因。而直流偏磁的引入不仅对交流变压器产生影响，同时还会向系统注入谐波，影响电能质量。分析了直流偏磁产生原因，以及对电力系统的危害，同时提出了一种基于换流站操作的直流偏磁抑制策略。利用该策略，当直流输电系统因保护动作导致单极闭锁时，自动地由大地回线模式装换为金属回线方式。由此可以极大地减小接地极流过大电流的实现，有效抑制直流偏磁。%The large current through the grounding electrode of DC system is the main reason for DC magnetic bias which cau -ses DC current running through the neutral grounding transformer .Whereas the introduction of DC magnetic bias can not only affect AC transformers , but also can inject the harmonic wave into the system , which would influence the power quality .The reasons for the generation of DC magnetic bias are analyzed as well as its harms to the power system , and meanwhile a sup-pression strategy for DC magnetic bias based on the operation of the convertor station is proposed .Using this strategy, when the DC transmission system experiences the unipolar locking due to the protection action , the ground loop mode automatically changes to the metal mode , which greatly reduces the heavy current running through the grounding electrode and suppresses DC magnetic bias effectively .