Research of Suitable Frequency Band of Transmission Line Model for Pilot Protection

In the research of relay protection, transmission lines are usually imitated with different mathematical models. But the mathematical model only corresponds with actual physical model approximately when applied in the special frequency band. So it has to consider the suitable frequency band when implementing the relay protection. This paper raises the definition of suitable frequency band of line model applied to pilot differential protection based on parameter identification. And it researches the suitable frequency band of transmission line Pi model. It appears that the suitable frequency band becomes narrower with the increase in the length of transmission line, and is irrelevant with the system impendence. Finally, simulations by ATP basically establish the suitable frequency bands of Pi model for the transmission lines of different length, providing the criteria for the design of digital filters of pilot differential protection based on parameter identification.