基于电压回升比的混合直流线路主保护新原理

A New Principle of Main Protection for Hybrid HVDC Lines Based on the Voltage Recovery Ratio

由于混合直流输电系统电网换相换流器--模块化多电平换流器(line commuted converter-modular multilevel converter,LCC-MMC)存在弱边界特性,电网换相换流器(line commuted converter,LCC)侧耐受过渡电阻能力较弱,导致现有的高压直流线路行波保护原理适应性不足。在定量分析直流线路边界特性和故障特征的基础上,针对LCC侧线模电压首行波波头的“尖峰-回落”特征,构建了基于线模首行波电压回升比的主保护新原理。通过计算保护时窗内电压跌落值和回升值之比判别故障区域,并提出了消除保护死区和识别雷击干扰的辅助判据。仿真结果表明,所提方案能在100μs内实现故障选区,且对采样率、对侧电抗器数值、过渡电阻和雷击干扰等具有较好的鲁棒性,较现有行波保护原理具有明显的性能提升。

Due to the weak boundary characteristics of the LCC-MMC(Line commuted converter-modular multilevel converter)hybrid DC transmission line,the LCC side appears to have a weak capacity to withstand transition resistance,resulting in insufficient adaptability of the existing HVDC traveling wave protection principle. Based on the quantitative analysis of the boundary characteristics and fault characteristics of the DC line,in view of the "spike-fall" characteristic of the first traveling wave head of the LCC side line-mode voltage,this paper constructs a novel main protection principle based on the line-mode voltage recovery ratio of the first traveling wave. The ratio of voltage drop value and rebound value within the protection window is calculated to identify the fault zone,and auxiliary criteria for eliminating protection dead zone and identifying lightning disturbance are proposed. Simulation results show that the scheme can realize fault identification within100 μs,and has better robustness to sampling rate,opposite-side reactor value,transition resistance,lightning disturbance,etc.,which shows an obvious performance improvement compared with the existing traveling wave protection principle.