SYMMETRICAL COMPONENT BASED IMPROVED FAULT IMPEDANCE ESTIMATION METHOD FOR DIGITAL DISTANCE PROTECTION .1. DESIGN ASPECTS

Recently, distance relays using digital processors have received considerable attention from researchers. The digital processor based distance relays use estimates of fault impedance (distance) in making decisions. Several methods have been suggested in the past that can be used to estimate fault distance. Researchers have proposed symmetrical component, Clark's component and modal component theories for developing distance estimation methods. The approach used in the symmetrical component based methods has resulted in a higher computational burden on the digital processor, which was addressed using special hardware or multiprocessors. In the present paper, an improved method is proposed that also uses symmetrical component transformation. The simplified approach used in the proposed method leads to a computational advantage over previously suggested symmetrical component based methods. The paper derives performance equations that are valid for ten types of shunt fault encountered on transmission lines. The basis for analyzing shunt faults on the transmission line model and developing the fault estimation method is discussed in detail. The proposed method is also validated using numerical examples, the results of which are reported in Part II of this paper (Electr. Power Syst. Res., 26 (1993) 149-154).