Development of Digital Step Out Relay for 2bit Transmission System and the Improvement Way of Limit Detection

We selected the way of “56V” system, which have the ability of high performance of section detected function, as the step out detection system for 500kV connective transmission line. Conventional “56V” system was using 4bit on transmission format of PCM relay. This time, we have developed new “56V” system which is using 2bit. It is confirmed that this 2bit system has the equal ability to 4bit system. On the other hand, the “56V” system has the limitation to detect step out with high slip frequency or low voltage. We have developed combination system, which have the ability of section detected function of “56V” system and “56Z” system, and we confirmed the high performance of step out detection system by verification test of the system.