A New Method to Identify and Blocking Inrush Current in Transformer

In this research, in relation to the basics of the theory of inrush current and the methods of preventing the operation of the differential relay error in the protection of the power transformer, some materials will be presented. Then the example of differential relay malfunctions is discussed. Since the incorrect operation of the differential relay causes the inappropriate disconnection of important network equipment such as power transformers, it creates irreparable tensions in the stability of the network, especially in sensitive times such as peak load, so it is necessary to prevent the aforementioned error by using various blocking methods. For this purpose, by examining the methods used in relays manufactured by reliable companies such as 7UT633 relay manufactured by SIEMENS company, MICOM P54x relay manufactured by Schneider Electric company, RET670 relay manufactured by ABB company, T30 and T60 relay manufactured by GE company, SEL587 relay manufactured by Schweitzer company, the logic of their operation when inrush current occurs We will observe the presence of errors in the operation of these relays when switching the transformer. In the end, by presenting a method based on the logic of frequency analysis to block the relay when the phenomenon of inrush current occurs (Frequency Blocking Algorithm), we will improve the performance of the relays and prevent the differential relay error when energizing the transformer.