基于故障负序分量的低频变压器快速差动保护

Fast Differential Protection of Low-frequency Transformer Based on Fault Negative Sequence Component

低频变压器是低频输电系统的核心器件之一。实验表明低频系统的故障暂态过程多变,低频变压器的短路电气量特征与常规变压器有较大差异。由于励磁涌流判据开放速度缓慢,低频变压器发生区内故障时常规纵差保护的速动性受到影响。文中提出了基于故障负序分量方向原理的低频变压器快速差动保护。首先,分析了模块化多电平矩阵变换器(M3C)低频输电系统的变压器区内故障特性以及M3C换频器响应情况;其次,分析了负序计算的数值方法对负序差动影响,并通过分析低频系统故障初期的窗口时间内的负序特征,提出了故障负序分量方向的判别方法;进一步,讨论了该方法在变压器非正常工况下对励磁涌流如何区分判别。最后,以实际工程为例建立仿真模型,针对典型区内故障对所提方法进行了仿真验证。

Low-frequency transformer is one of the core components of low-frequency transmission system.Experiments show that the fault transient process of the low-frequency system is variable,and the short-circuit electrical characteristics of low-frequency transformers are quite different from those of conventional transformers.Due to the slow unblocking speed of the excitation inrush current criterion,the rapidity of the conventional longitudinal differential protection is affected when the low-frequency transformer has an internal fault.This paper presents a fast differential protection for low-frequency transformer based on the principle of fault negative-sequence component direction.Firstly,the transformer internal fault characteristics and the response of the modular multilevel matrix converter(M3C)in the M3C-based low-frequency transmission system are analyzed.Secondly,the influence of the numerical method for negative-sequence calculation on the negative sequence differential is analyzed.and the identification method of the negative sequence component direction of the fault is obtained by analyzing the negative sequence characteristics in the window time of the initial phase of the low-frequency system fault.Furthermore,the discrimination of excitation inrush current under abnormal conditions of transformer is discussed.Finally,a simulation model is established by taking an actual project as a case,and the proposed method is verified by simulation for typical internal faults.