Hitachi, Ltd.

The Tokyo Electric Power Company, Incorporated

Masami Okamura

Yoshihiro Sano

Yoshiteru Miki

Hiroshi Sasaki

Junichi Makino

Kazuo Seo

Yoshihumi Oura

Fumio Aoki

Jun-ichi Makino

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.

Coding equipment providing compressed code

Protection of an electric power system is attained under control of a digital computer. Voltage and current of the electric power system to be protected are subjected to sampling at a predetermined sampling frequency and are applied to the computer after being converted into digital signals. The computer computes the product of these two digital signal inputs. The signal thus obtained is added to a preceding signal representing the product of voltage and current taken at time before a predetermined period of time so that unnecessary frequency components included in these signals can be removed. Then, the level of the resultant signal (which is free from the unnecessary frequency components) is compared with the level of a reference signal. When the former is greater than the latter, there is a fault in the electric power system, and necessary protective measures are taken to protect the electric power system.

Protective relaying system

Growing community of inventors

Musashino, Japan

Masami Okamura