Technological Advance in Relay Protection: Dangerous Tendencies

Abstract

1. EXTRUSION INTO THE HISTORICAL DOMAIN For over a hundred years all the tasks of relay protection have been performed by electromechanical protection relays (EMR). The fact that EMRs are still widely used in many countries, including Russia (about 80-90% of all types of protections), proves that in general EPRs are capable of solving all the present problems of the relay protection. However, during the past 15-20 years there has been a widespread displacement of EMR by microprocessor-based relay protection devices (MPD). MPD and various programmable logic controllers (PLCs) that control the operating modes of electrical equipment, have become an integral part of our lives and, in many cases, there is no other device available to substitute for them to ensure the normal functioning of the power industry. This is not due to some unique features of microprocessor devices, this is rather a result of the costs of the fully automated production of MPD based on printed circuit boards compared to the production of high-precision mechanics for the relays of the previous generation. 30-40 years ago due to the necessity for cutting production costs and improve profitability of production, the development of the new types of EMRs was stopped and all efforts were focused first on the creation of the static solid-state protections, and then on the development of MPDs. The first types of MPD simply copied all the functions and characteristics of the relays of previous generations. New features and capabilities of MPD have been implemented only many years after. This technical policy of manufacturers has resulted in the complete halting of the production of all other types of protection by all of the world's leading manufacturers of the relay protection, and MPDs have become nearly the only available type of protection. Even the very first MPDs, which simply copied the functions of the static solid-state transistor-based relays, see Fig. 1, revealed serious problems of the MPDs: more frequent failures and irreparability due to the presence of the special microprocessor and non-volatile memory containing the program. As a result, while the relays of type RXIDF-2H built on transistors and other discrete components were quick to repair and return to operation, their microprocessor-based analogue RXIDK-2H must be discarded. Hence, the microprocessor-based RXIDK-2H have long been taken out of service while RXIDF-2H are still used. The tendency of the relay protection reliability weakening associated with the transition to the MPD and noticed at the beginning of this process can be traced so far, despite the fact that modern generation of the MPDs have little in common with the first samples manufactured a few decades ago, see Fig. 1. This goes to prove that the problem is systemic rather than a result of the single technical defects specific to early MPD models. But no one wanted to gain the character of retrograde and nobody wanted to talk about the obvious problems of MPDs welcomed with such rapturous applause.