Research on pilot differential protection based on parameter identification and suitable frequency band of transmission line model

In order to improve characteristics of pilot protection, a new pilot differential protection based on parameter identification is proposed. In this new approach, the transmission line is dealt as PI model. As we know, the simplified PI model can only match physical lines within limited frequency band, which is defined as suitable frequency band (SFB). In order to apply the new approach, it is important to analyze SFB of PI model of transmission lines. From the view of application, this paper presents a definition of SFB and analyzes the influencing factors of SFB, compared with more accurate distributed transmission line model. The analytic and simulation analysis show that the SFB of PI model becomes narrower with the increase in the length of transmission line, and is irrelevant with the system impendence. This conclusion is useful for the design of digital filters while applying the new protection technique. Finally, simulations by ATP verify that the suitable frequency bands have significance on the selectivity and rapidity of pilot differential protection based on parameter identification.