基于故障全电流多阶突变的换流器并网线路纵联保护

Pilot Protection for Converter-interconnected Lines Based on Multi-stage Mutation of Fault Current

电力电子换流器的引入改变了传统电网的故障特性,当交流线路发生故障后传统差动保护难以满足保护需求,易出现灵敏度降低甚至拒动风险。针对此问题,提出基于故障全电流多阶突变的交流线路保护原理。该保护以故障发生后线路两侧电流波形形变特征、突变特征的规律变化为基础,通过矩阵梯度算法对两侧全电流信号进行突变特征值的提取,即对两侧全电流信号的突变程度进行描述,进而构造纵联保护。相比于传统暂态量的快速保护无须提取固定频段特征,所提方法克服了在短路电流受控情况下利用周期分量算法无法精准提取固定暂态量的问题,相比于直接采用常规暂态信号的保护,具备较好的耐受过渡电阻以及噪声的能力。最后在PSCAD/EMTDC中搭建了换流器并网系统的仿真模型并校验了保护的有效性,所提保护故障识别时间小于7.5ms,即使在经100Ω的过渡电阻故障情况下,仍然具有较高的灵敏度,能较好地满足换流器并网线路对保护速动性与选择性的需求。

The introduction of power electronic converters has altered the fault characteristics of the traditional power grids.Traditional differential protection is inadequate to meet protection requirements when AC lines experience faults,leading to reduced sensitivity and even the risk of refusal to operate.To address this issue,a principle of protection for AC lines based on multi-stage mutation of total fault current has been proposed.This protection is founded on the characteristic changes in the waveform deformation and mutation features of current on both sides of the line after a fault occurs.The matrix gradient algorithm is employed to extract the mutation feature values of total current signals on both sides,describing the degree of mutation in the total current signals and thereby constructing longitudinal protection.In comparison to traditional fast protection based on transient quantities that do not require the extraction of fixed frequency band features,the proposed method overcomes the challenge of accurately extracting fixed transient quantities using the periodic component algorithm under controlled short-circuit current conditions.In contrast to protection using conventional transient signals directly,it exhibits good tolerance to transitional resistance and noise.Finally,a simulation model of the converter grid-connected system is built in PSCAD/EMTDC to validate the effectiveness of the protection.The proposed protection achieves fault identification in less than 7.5 ms and and maintains high sensitivity even in the presence of a transitional resistance fault of 100Ω,meeting the requirements of fast response and selectivity for inverter-interconnected lines.