抄録
The protection relay changed from electromechanical or analog static type to digital type using the progress of microprocessor against the growth of power network. The digital relay improved protective performance and reliability based on establishment of various protection schemes and the embedded automatic supervising function using the development of the digital technique. Additionally, the recent protection system technique enable to make the configration and operation of power system efficient. Multi-terminal transmission lines can be realized by use of PCM current differential relay. The out-of-step protection, the voltage stability control and the over load failure extension protection can increase transmission capacity.
In future, it will need to develop the protection system for the distributed power generation and decrease the cost of protection systems against the progress of deregulation.
