ABSTRACT

Overcurrent protection relays are the basic components in a majority of types of powerful electrical and electronic devices and also have uses in power engineering. Analysis of the trends in relay technology development shows that the major relay developers do not share a solid and consistent direction for simple current relay design improvement. For instance, some experts reason that certain families of electric-mechanical relays currently in mass production need to be replaced by static integral microcircuit (IC) relays. At the same time, they claim that regular electric-mechanical relays (including the simple overcurrent relays) are the most reliable and affordable for many electric utility companies, and will, therefore, be used in the majority of control and protection systems. It is important to note that the modern electric-mechanical relay is a high-speed device, which is insensitive to pulse and high-frequency interference and surge voltage. It exhibits a very robust behavior in overload modes and has a satisfactory reset ratio. One has to agree, though, that electric-mechanical relays usually consist of many expensive, high-precision components, the production of which becomes inefficient for the relay manufacturer. A dynamic measuring system with exposed contacts reduces the required relay reliability in a dust- and gas-intensive environment under a constant vibration factor. Besides, the need to clean and adjust the contacts contributes to increased labor-intensive maintenance.