Boundary Protection, A New Concept for Extra High Voltage Transmission Lines --- Part I: Spectrum Analysis of Fault Induced Transients

This paper introduces a new concept for EHV transmission line protection, the boundary protection, which can instantly discriminate faults at any point of the protected line relying on only single-ended measurement of the fault induced transient information. Part I of the paper introduces the time-frequency spectrum characteristics of fault-induced transients. The spectrum analyses show that: (i) the frequency spectra of transients vary with time; (ii) the spectra are mainly determined by the frequency features of reflection and refraction coefficients of the line boundary; (iii) the fault information is embodied in the period of time Deltat after fault inception; (iv) within the Deltat, the frequency spectrum ratio of backward to forward traveling-waves is larger than 1 in the case of a fault from the forward direction, but close to zero for a reverse direction fault; (v) within Deltat , the frequency spectrum of high-frequency components induced by internal faults is much larger than that by external faults. Based on the conclusions above, the fault discriminative criterions of the boundary protection are derived and given in Part II of the paper. The tests using both the results from EMTP simulation and from recorded field-data demonstrate the feasibility of the boundary protection