Abstract: Transmission lines have both their terminals connected with bus lines through breakers, respectively, and connected to earth through earth switches, respectively. Protecting relay devices are fed with not only the outputs of voltage transformers and current transformers but also the contact signals made coactive with the breakers and earth switches at the terminals considered. Those contact signals are transmitted through signal transmission devices to the other terminals, and the contact signals of the breakers and earth switches at the other terminals are transmitted. The protecting relay devices detect the fault of the transmission lines, if any, to trip the breakers and to confirm the open states of the breakers from the breaker contact signals of the terminals considered and the other terminals thereby to close the earth switches.

Abstract: In a parallel digital signal delivered from an AD converter, "1" appearing in a bit position nearest to the most significant digit (MSD) is detected, and the parallel digital signal is converted into a serial digital signal consisting of a weight character indicating this specific bit position and a data character indicating the numerical value of the data. Further, a weight bit is provided for changing the weight of the output of the AD converter depending on the analog quantity subjected to AD conversion so as to reduce the number of bits required for coding the parallel signal.