共用接地极直流输电工程运行方式转换过程中换流站地网分流的影响及解决方案

Influence and Countermeasures of the Shunt Current of the Grounding Grid of the Converter Station in Operation Modes Conversion for HVDC Transmission Project with Common Ground Electrode

分析了共用接地极直流系统在单极大地和单极金属回线运行方式转换过程中存在的风险,包括对变压器、开关等设备以及控制保护的影响。提出了在高速接地开关(high speed grounding switch,HSGS)与站内地网间装设限流电阻和与之并联的隔离开关的新型接线解决方案以及接地限流电阻的阻值设计方法。通过理论分析和现场调试验证了直流运行方式转换过程中的限流效果和对中性线电压的影响,通过PSCAD/EMTDC仿真分析了接地方式对直流系统故障暂态工况的影响,结果表明所提出的方案可有效解决直流运行方式转换过程共用接地极对换流站的相互影响,并不影响极线和中性线直流设备的稳态和暂态应力要求。对于直流控制保护设计,已建工程仅需修改顺控,无需修改保护配置。

Analysis is carried on the risks of the DC system with common ground electrode in the process of monopolar metallic and ground return mode conversion,including the impact on equipment,such as converter transformers and switches,as well as control and protection system.A new wiring solution for solving the influence is proposed to install a current-limiting resistor and its bypass switch between the high-speed grounding switch(HSGS)and the grounding grid of the converter station.The resistance design method of the grounding current-limiting resistor is also given.The limited current and the neutral line voltage in the process of DC operation mode conversion are proposed based on theoretical analysis and verified by commissioning.The influence of the grounding method on the DC system during the fault transient conditions are analyzed by PSCAD/EMTDC simulation.The results show that the solution can effectively solve the mutual influence of the common grounding electrode on the converter station during the conversion process of the DC operation mode,and does not affect the steady-state and transient stress requirements of the polar line and neutral line equipment.For the DC control and protection design,only the sequence control needs to be modified for the built project,and the protection configuration does not need to be modified.