Research of boundary protection unit based on phase information of the improved recursive wavelet transform for EHV transmission lines

On the basis of analyzing the frequency characteristics of EHV transmission line boundary, this paper presents a novel principle and algorithm of boundary protection unit for extra-high-voltage transmission lines. The protection algorithm utilizes the improved recursive wavelet transform (IRWT) to extract the desirable frequency components of fault-induced transient signals. And then the IRWT measures the phase information of the signal components and concludes the average frequency which is the highest frequency existing in transient signal. According the difference of the average frequency value of the extracted signals, an internal or external fault can be distinguished. The extensive PSCAD/EMTDC simulation results show that the new proposed protection algorithm is insensitive to fault type, fault resistance, fault location and fault initial angle. And the boundary protection unit based on IRWT phase information is feasible and effective.