Grid connection of renewable energy-based power sources is expected to grow in the coming years. By replacing dedicated communications equipment with general-purpose Ethernet, the developed device enables a greater degree of freedom in transmission line configurations and helps lower overall protection relay system cost. Hitachi has recently developed a transmission line protective relay device that uses a layer 2 (L2) switch (a general-purpose Ethernet communications device), making it possible to use a general-purpose Ethernet interface instead of a dedicated communications board. The plesiochronous digital hierarchy (PDH) communications method has conventionally been used along with a dedicated communications control board mounted on the protective relay device. These devices were developed about 30 years ago, and have always used power company communications equipment for data transmission. They transmit current data back and forth between terminals and calculate the differential current to detect whether a failure has occurred in the applicable line interval. Pulse code modulation (PCM) current differential relays are protective relay devices for transmission lines. For example, general-purpose communications technologies that enable high-speed, high-capacity communications such as Ethernet communications and the Internet Protocol (IP) are becoming increasingly commonplace. The rapid advancement of the information-oriented society in recent years has resulted in increasingly advanced communications network technology.
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