换流变压器阀侧接地故障分析及保护优化

换流变是高压直流输电系统的重要组成部分。换流变阀侧自身无接地点,但直流侧有接地点,当换流变阀侧区内发生单点接地故障时,随着换流阀的导通和关断,故障电流呈现不规则的变化,换流变自身现有保护可能灵敏度偏低。极端情况下,当Y/Y接线变压器阀侧中性点发生接地故障时,换流变自身主保护无法快速动作。文中从换流变的结构及运行工况出发,定性概括了阀侧接地故障后的电流特征;分析了现有保护系统的特性;提出了基于零序差动和快速零序过流原理的换流变阀侧保护优化方案;并结合现场故障录波及实时数字仿真系统仿真波形对其进行了验证。验证结果表明,优化后判据可以有效提高换流变保护在阀侧区内单点接地故障下的灵敏度、动作速度及故障定位准确度。

Analysis and protection optimization of grounded fault in valve side of converter transformer

Converter transformer is an important part of HVDC transmission system. There is no grounding point in the AC side of converter valve, but there is grounding point in the DC side. When one phase grounded fault occurs in the valve side of converter transformer, the fault current changes irregularly with the opening and closing of the converter valves, and the sensitivity of converter transformer protection is usually low. In extreme cases, when the neutral point of YY-connected transformer valve side grounded fault occurs, the protection of converter transformer itself can not trip quickly. Based on the structure and operating conditions of converter transformer, the current characteristics of valve side grounded fault are analyzed, and the characteristics of existing protection are analyzed. Based on the principle of zero sequence differential protection and fast zero sequence overcurrent protection, an optimization scheme of existing converter valve side protection is proposed. It is validated by fault record form a converter substation and simulation waveform from RTDS. The results show that the optimization scheme can effectively improve the sensitivity, operating speed and fault location accuracy of the converter transformer protection under the one phase grounded fault in the valve side.