Transformer differential protection using positive sequence current; design and implementation

This paper describes the complete design of a prototype digital protective relay for three-phase transformers using positive sequence current. The major emphasis of the paper will be on the detailed description of the hardware and software of the prototype relay. The relay hardware consists of a data acquisition board and a microcomputer board which is based on the 80188 processor and input/output board. Sample real-time test cases are included in the paper. Performance studies results show that the proposed algorithm performs very well to recognize the various conditions in power transformers. The outstanding advantage of the proposed method with respect to the previous approaches, is requirement to less number of units for differential relay.