采用数学形态学防止变压器差动保护误动的新方法

A NEW ALGORITHM BASED ON THE MATHEMATICAL MORPHOLOGY FOR AVOIDING MAL-OPERATION OF TRANSFORMER DIFFERENTIAL PROTECTION

为有效地防止变压器区外故障TA饱和引起的差动保护误动,该文提出了一种基于数学形态梯度实现TA饱和检测的新方法。与传统的“时差法”不同,该方法仅需要对故障发生时刻进行检测,不需要对差流出现时刻准确定位,通过对故障后的一小段差流波形进行适当变换,构造出新的电流波形,然后利用数学形态梯度进行处理,提取出电流波形特征,从而实现在TA严重饱和的情况下,对差动保护区内外故障的准确识别。新方法计算简单,快速可靠,EMTP仿真实验验证了该方法的可行性和有效性。

To avoid the mal-operation of transformer differential protection when out-zone fault occurs under current transformer（CT） saturation, a new algorithm based on the mathematical morphology is put forward in this paper. Unlike the traditional time-differential method, which is based on the time difference between fault occurrence and the differential current increase, this algorithm only needs detecting the time of fault occurring, while the time of differential current increasing is no more needed. A new current waveform is obtained by a symmetrical transformation of the initial part of differential current after fault occurred, and then its characteristic is extracted by morphological gradient. In the case of CT＇s serious saturation, a discrimination of out-zone fault and inner-zone fault can be clearly made by this algorithm, which needs a little calculation and a short data window. Simulation results of EMTP validate its feasibility and reliability.