±420 kV中国渝鄂直流背靠背联网工程系统设计

System Design of±420 kV Chongqing-Hubei Back-to-Back HVDC Project of China

与前期工程相比,±420 kV中国渝鄂背靠背联网工程系统设计的主要难点在于工程直流电压较高、容量较大,且故障穿越、交直流保护等要求提升,但全控电力电子器件的暂态应力配置水平有限且交流电网极端运行方式恶化。针对器件暂态应力配置水平受限,文中提出了精确的换流器桥臂故障电流上升率计算方法、阀控过流保护的分桥臂闭锁策略、阀本体过压保护的动态过压定值策略,解决了弱器件能力下无法兼顾设备安全性和故障穿越能力的问题。针对极端运行方式下交流电网和柔性直流系统高频失稳和弱系统失稳问题,分别提出了失稳机理及解决失稳的工程实用方法。针对接入500 kV交流电网带来交流断路器失灵保护和直流差动保护的特殊要求,提出了相应的解决对策和建议。

Compared with the previous projects,the main difficulties are raised in the system design of Chongqing-Hubei project of China are the higher engineering DC voltage,larger capacity and raised requirements for fault ride-through and AC/DC protection etc.,but the endurable transient stress level of fully-controlled power electronic devices is limited and the extreme operation mode of AC power grid deteriorates.In view of the limited endurable transient stress level of the device,this paper proposes the accurate calculation method of rising rate for the arm fault current in the converter,the independent arm blocking strategy of the overcurrent protection for the valve controller,and the dynamic setting strategy of the valve over-voltage protection.These measures solve the problem that the device safety and fault ride-through requirement cannot be both satisfied under the weak component capability.Aiming at the problems of high-frequency instability and weak-system instability of the AC grid and flexible DC system in the extreme operation modes,the instability mechanism and the practical engineering methods solving the instability are proposed.To meet the special requirements of AC breaker failure protection and DC differential protection under the access of 500 kV AC power grid,the corresponding solutions and suggestions are proposed.