考虑直流控制系统影响的HVDC输电线路后备保护研究

在考虑直流控制系统影响的情况下,详细分析了HVDC输电线路区内、区外的故障特征以及直流控制系统的动作特性和控制状态。引入并分析了基于开关函数的交直流系统二次谐波计算等值模型。通过分析故障期间换流器触发角和直流侧二次谐波量的变化特征,提出了一种新的以换流器触发角为保护动作量,利用二次谐波分量闭锁的直流线路后备保护方案,给出了保护整定的理论计算方法。与直流线路纵联差动保护相比,该保护不因直流电流波动影响而被闭锁,保护动作时间较快;与微分欠压保护相比,具有更高的抗过渡电阻能力。通过PSCAD/EMTDC大量仿真计算,验证了该保护能可靠区分直流线路区内、区外故障,与直流线路纵联差动保护和微分欠压保护相比具有明显的优越性。

Backup protection research for HVDC transmission line considering the impact of DC control system

The fault characteristic and the states of DC control system during HVDC transmission line inner and external fault are analyzed in detail considering the influence of DC control system. An equivalent circuit of second-order harmonic based on switch function theory is introduced and analyzed. A new backup protection scheme for DC transmission line is proposed by analyzing the feature of converter firing angle and second-order harmonic in failure period. Converter firing angle is used as operating value and second-order harmonic is used as blocking signal for the backup protection. In addition, theoretical calculation method for the protection settings is provided. Compared with DC line differential protection, the proposed protection can operate with higher speed and will be independent of DC current fluctuations. Compared with derivative under-voltage protection, it can operate well during much higher resistance ground fault. Comprehensive simulation using PSCAD/EMTDC validates that the presented protection scheme can identify inner and external fault reliably and rapidly, and has obvious advantages over DC line differential protection and derivative under-voltage protection.