The basic theory of boundary protection for EHV transmission lines

Transmission line protection based on transient components without communication links is called boundary protection. The basic theory of boundary protection is described in the paper. By analyzing the fault-induced transients, it is found that the different characters of transients at single-end between the internal and external faults are decided by the frequency characteristics of reflection and refraction coefficients of line boundary. The different time-frequency characters of transient components between internal and external faults are discovered based on analyzing the frequency response of reflection and refraction coefficients of line boundary. The boundary protection schemes can be constructed guided by the theory.