ABSTRACT
One of the main reasons usually presented in the vindication of Digital protection relays (DPR) advantages is the considerably higher reliability of DPR, ostensibly, in comparison with electromechanical and electronic relays. The unconditional statement about the greater reliability of semiconductor relays over electromechanical relays is a popular mistake. DPR reliability is lower than the reliability of electromechanical relays and electronic relays on discrete elements. In many electric power systems, electromechanical relays until reliably protected many crucial power installations of all voltage classes and other utilities equipment. Sometimes, electromechanical protective relays include working in parallel with microprocessor-based relays for maintaining greater reliability of the important electric installations and especially crucial equipment. In contrast to isolated measuring and monitoring of computer systems, the protective relay is associated directly with the possibility of destructive impact on power system modes. The managers making decisions in the field of relay protection and personnel of the power companies should be informed about these DPR features.
