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

In the research of relay protection, transmission lines are usually imitated with different mathematical models. But the mathematical model corresponds with actual physical model approximately only when it is 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 Π model. It appears that the suitable frequency band becomes narrower with the increase of the length of transmission line, and is irrelevant with the system impedance. Finally, simulations by ATP basically establish the suitable frequency bands of Π model for the transmission lines of different length, provides the criteria for the design of digital filters of pilot differential protection based on parameter identification. And it verifies that the suitable frequency bands have decisive effect on the selectivity and rapidity of relay protection.