Improved line current differential protective relaying method and relay for in-zone tapped transformers

摘要

A method for providing protective control to a tapped line in a power system, comprises the steps of measuring one or more local currents in a first protection element ; receiving, in the first protection element, one or more remote current measurements from a second protection element ; calculating one or more differential currents based on the local and remote current measurements ; calculating one or more restraining currents based on the one or more differential currents ; outputting a first protective control signal based on the differential currents and the restraining currents ; determining one or more zero sequence currents ; subtracting the zero sequence currents from the local and remote current measurements to generate modified current measurements ; calculating one or more modified differential currents from the modified current measurements ; calculating one or more modified restraining currents from the modified current measurements ; and outputting a second protective control signal based on the modified differential currents and the modified restraining currents.