Influence Of ECT And CT Mixing On Differential Protection Of Line

In recent years,the smart substation as the core of smart grid has made great progress,with the strong smart grid planning proposed by the national Power Grid Corp.However,at present stage,not all substations can be built intelligent substations at the same time.This leads to a large number of transmission lines,one side is the electronic current transformer(ECT)used by the intelligent substation,and the other is the electromagnetic current transformer(CT)used by the traditional substation.Due to the difference of transmission characteristics,when ECT is mixed with CT in transmission lines,it may cause incorrect operation of differential protection.Based on the Jiangxian-Zhongyang line which occurred this type errors as the research object,this paper has finished following works:First,the paper referred to the existing research on CT and ECT.used the parameters of current transformer in the Jiangxian-Zhongyang line,and reappeared the simulation of the transmission characteristics of two types of current transformers,and analyzed the factors that affect the CT saturated.Forshadowing the next step of analysis and research.Then,to directed against the saturation problem of electromagnetic current transformer,an improved S transform method is proposed to detect the saturation time domain of CT secondily current.And build the model of the Jiangxian-Zhongyang line on PSCAD,set up the fault to realize CT saturation,and then test the effectiveness and advantages of the improved S transform method to detect the CT saturation.Finally,according to the analysis of the CT and ECT transmission characteristics,some researches of differential protection and the fault recorded wave graph obtained from the Jiangxian-Zhongyang line.the reason why differential protection error actes is the CT saturation.Then used the improved S transform method detect CT saturation in differential protection.And build the model of the Jiangxian-Zhongyang line,make the fault occur in the region andoutside the region.It is proved that this method is useful to prevent the misoperation of the differential protection caused by the mixing of ECT and CT.