和应涌流导致差动保护误动原因分析

和应涌流可能引起运行变压器或发电机的差动保护误动,影响变压器与发电机的正常运行.目前,还没有防止和应涌流引起相关差动保护误动的有效措施,现场主要是靠二次谐波励磁涌流判据或三次谐波电流互感器饱和判据起到一定的闭锁作用.首先结合和应涌流的特点分析了与其相关的差动保护误动的原因主要在于电流互感器发生饱和,进一步通过多起现场误动实例与仿真,着重分析了不同类型的和应涌流发生时,电流互感器饱和检测判据所起到的闭锁作用.结果证明,虽然电流互感器饱和判据在变压器级联形式下能起到一定的闭锁作用,但在变压器并联或与多电源相连时很难起到较好的闭锁作用.

Analysis on Mal-operation of Differential Protection Caused by Sympathetic Inrush

It is increasingly known that the sympathetic inrush may cause the mal-operation of differential protection for transformer or generator,and affects their normal running.Up to now,because the effective measure is no available to identify the sympathetic inrush,the second harmonic restraint scheme against initial inrush and third harmonic based current transformer(TA)saturation criterion are used to prevent differential protection to mal-operation caused by the sympathetic inrush.Considering the characteristics of sympathetic inrush,it is analyzed that mal-operation of differential protection related to sympathetic inrush is mainly due to the TA saturation.Further,through the mal-operation cases in practice and simulation results,the effectiveness of TA saturation criterion is analyzed under different connections between transformers,such as in parallel,in series and their coexisting.The analysis results verify that the TA saturation criterion can play a certain role in blocking the differential protection for transformer connection in series,but it may be invalid under transformer connection in parallel or parallel and series coexisting.