柔性低频输电系统换流站故障后瞬态过电压

Transient Overvoltage After Faults in Converter Station of Flexible Low Frequency Transmission System

柔性低频输电兼具工频交流和直流输电的技术优势,在海上风电送出、新能源汇集以及城市电网柔性互联等场景具有应用潜力。柔性低频系统换流站故障及后续闭锁阶段会产生较严重的瞬态过电压,影响站内参数设计和绝缘配合。为此,针对柔性低频输电系统换流站典型拓扑和参数,建立了过电压仿真模型,对典型故障后瞬态过电压进行仿真研究;结合故障后过电压产生特点,将故障后的过程分为4个暂态阶段,分别分析了各阶段中不同位置的过电压特征以及产生原因。在考虑不同的故障工况和对应保护动作策略的条件下,仿真计算了换流站关键位置和设备的最大瞬态过电压水平,提出了换流站避雷器配置方案,并验证了其对瞬态过电压的抑制效果。研究结果表明:故障发生、换流器控制响应、换流器闭锁以及断路器断开的4个瞬态过程均会在换流站内不同位置产生过电压,其中换流器闭锁阶段的过电压水平最高;在不考虑抑制措施时,220 kV区域的瞬态过电压标幺值可达3.28,桥臂电抗器端间过电压标幺值可达3.83;所提避雷器配置可以有效抑制过电压,且各避雷器吸收的能量符合要求。研究结果可为柔性低频换流站参数设计及绝缘配合提供依据。

Flexible low-frequency transmission technology combines the advantages of both power frequency transmission and direct current transmission,and has potential application in scenarios such as offshore wind power transmission,renewable energy collection,and flexible interconnection of urban power grids.There are severe transient overvoltages of flexible low frequency converter station after faults and subsequent blocking process,which affects station parameter design and insulation fit.In this paper,an overvoltage simulation model is established for the typical topology and parameters of the flexible low frequency converter station,and a simulation study of the transient overvoltage after a typical fault is conducted.Based on the characteristics of overvoltage generated after faults,the process after faults is divided into four transient processes,and the overvoltage characteristics and causes of different positions in each process are analyzed.Different fault conditions and corresponding protection strategies are taken into consideration,and the maximum transient overvoltage level of main positions and equipment in the converter station is simulated and calculated.Moreover,the arrester configuration and parameters of converter station is proposed,and the suppression effect on transient overvoltage is verified.The results show that there are transient overvoltages in the converter station generated in the four transient processes of fault occurrence,converter control response,converter blocking,and breaker disconnection.The overvoltage level in the transient process of converter blocking is the highest.When the suppression is not taken into consideration,the transient overvoltage level in the 220 kV region is 3.28 p.u.,and the overvoltage level between the branch reactor is 3.83 p.u.The proposed arrester configuration can effectively suppress the overvoltage,and the energy absorbed by each arrester meets the requirements.The research results can provide a basis for the parameter design and insulation coordination of flexible low-frequency converter stations.