Development of 765kV transformer protection relay

Currently, ultra-high-voltage (UHV) systems are under development in many countries around the world in order to accommodate the increasing levels in demand for electric power. In Korea, the commercialization of a 765kV ultra-high-voltage system has been ongoing since 2002. We have developed a number of protection relays suitable for the UHV system to enable us to make a contribution to the 765kV UHV projects in Korea. During the development of the protection relays for the 765kV UHV system we encountered several technical issues of particular interest in relation to the transformer protection relay. In this paper, we introduce a number of technical issues, such as a development undertaken in response to the need for an increase in transformer capacity to overcome consequent transmission restrictions, the implementation of a CT saturation countermeasure and the requirement for high-speed operation of the current differential elements. In order to provide solutions to these issues, we have undertaken several developments, which we explain in this paper. Furthermore, with the development of this UHV transformer protection technology, we have been able to complete the commercialization of the transformer protection relay for the 765kV UHV system.