考虑传输函数特性的行波幅值比较式纵联保护原理

为了精确描述行波在输电线路上的传播过程及其衰减规律,挖掘其携带的故障信息并应用于输电线路继电保护,将线路时域上的波动方程进行Laplace变换,分析了有损均匀传输线的戴维南等效电路,建立了故障附加网络的集总等效电路.在此基础上,推导出输电线两端初始反向行波的数学关系,并提出一种考虑传输函数特性的行波纵联保护算法.该算法利用S变换提取初始行波,计算线路两端初始反向行波的衰减比,依据衰减比识别区内外故障.最后,利用PSCAD/EMTDC仿真数据对保护算法进行测试,结果表明:区内故障时,衰减比大于0.81,区外故障时,衰减比接近0,说明保护算法能可靠识别区内外故障,从原理上克服了线路模型误差、线路参数不确定性等因素产生的不利影响. 

Pilot Protection Principle Based on Traveling Wave Amplitude Comparison Considering the Characteristics of Transfer Function

In order to accurately describe the propagation process of traveling wave and its attenuation law in the transmission line, and explore fault information that it carries for the transmission line protection, the equivalent circuit of Thevenin type for the lossy uniform transmission line was analyzed and the lumped equivalent circuit of the faulted network was built by transforming the transmission line wave equations in the time domain into the Laplace domain. On the basis of the lumped equivalent circuit, the mathematical relationship of the initial backward traveling waves on both ends of the faulted line was deduced, and the algorithm of the travelling wave based pilot protection was proposed, while the transfer function of the transmission line was taken into consideration. S transform was used to extract the initial traveling waves, and the attenuation ratio of the initial backward traveling waves on both ends of the line was calculated. The proposed algorithm determines whether a fault is internal or external to the protected zone according to the ratio value. The simulation data from PSCAD/EMTDC was applied to verify the proposed algorithm. The simulation results show that the ratio is greater than 0.81 when the internal fault occurs, and it almost equals to zero when the external fault occurs, indicating that the algorithm can reliably identify internal and external faults, and is not affected by the adverse factors of the error of line model, circuit parameter uncertainty, etc.