基于直流滤波环节暂态能量比的高压直流线路纵联保护

A Pilot Protection for HVDC Transmission Lines Based on the Ratio of DC Filter Link Transient Energy

为克服传统高压直流输电线路电流差动保护快速性差、耐受过渡电阻能力有限等问题,提出一种基于线路边界两侧特定频带能量比值的纵联保护方案。以直流滤波器阻抗-频率特性为基础,对直流输电线路区内及区外故障分量附加网络进行理论分析发现:区内故障时,对于线路两端的任意一端,其边界线路侧特定频带能量大于边界阀侧的值,两者之比较大;整流端(逆变端)区外故障时,整流端(逆变端)边界线路侧特定频带能量小于边界阀侧的值,两者之比较小。据此,可判别区内、外故障。大量仿真结果表明,该保护方案计算量小,能够快速识别区内、外故障,可靠地保护了线路全长,且耐过渡电阻能力强、不受分布电容影响。

Traditional current differential protection for high voltage direct current(HVDC)transmission lines has the disadvantages such as low tripping speed and limited ability to withstand high-impedance faults.Therefore,a novel pilot protection scheme based on the ratio of transient energy within the specific frequency band on both sides of the line boundary is proposed.Based on the impedance-frequency characteristic of the DC filter,the theoretical analysis on the fault-component networks corresponding to internal and external faults on the DC transmission line shows that,under an internal fault,for either terminal of the dc line,the transient energy within a specific frequency band on the line side of the boundary is much greater than that on the valve side of the boundary,and their ratio is large.Nevertheless,for rectifier-terminal(inverter-terminal)external faults,the transient energy on the line side of the rectifier-terminal(inverter-terminal)boundary is much less than that on the valve side of the boundary,and their ratio is small.Thus,it can be utilized to discriminate internal faults from external ones.Simulation results show that the proposed protection scheme with low computational complexity can identify the internal and external faults quickly,and can protect the entire line reliably.Besides,it can identify high-impedance internal faults and is not subject to the distributed capacitor of dc lines.