直流输电共用接地极线方式的保护特性

Protection Characteristics of HVDC Common Grounding Electrode Lines

分析了传统接地极保护用于共接地极线模式时存在的不合理性。利用电路原理对共接地极线模式下各类故障时的电气参数进行计算得出:当接地故障发生在共接地极线处时,故障点离接地极点越近,各系统的保护装置测得的不平衡电流越小;当接地故障发生在各自独立接地极线上时,故障点离直流开关站越近,故障侧的保护装置测得的不平衡电流越大,与正常运行侧的保护装置测得的不平衡电流情况相反。由此得出:断线故障时的不平衡电流为固定值;单线故障对过电压保护影响不大;双极运行系统不平衡电流对保护的影响与其流入方向和大小有关。最后,针对故障电流特性,建议对不平衡电流保护进行故障定位及反时限功能的改进。

The illogicality of the traditional grounding electrode protection used in the configuration of common grounding electrode lines is analyzed. Under the common grounding electrode lines configuration, the electric parameters under each type of fault according to the circuit theory are calculated. It can be concluded that the unbalanced current measured by the protection of every system becomes small when the fault on the common grounding electrode lines is near the grounding location. The unbalanced current measured by the protection equipped on the fault side becomes large when the fault is near the DC switch station in each grounding electrode line, and the unbalanced current measured by the protection equipped on the normal side is on the contrary. It is also concluded that the unbalanced current is fixed when single-line is broken, all the single- line-fault affect little to the over-voltage protection, and the unbalanced currents in the bipolar affect the electrode current unbalanced protection depend on its direction and magnitude. Finally, it is suggested that the current unbalanced protection should adopt fault location and the inverse-time function considering the characteristics of the fault circuit.