Application Of Self-Adaptive Technology In Transformer Differential Protection

Power transformer is one of the most important equipment in power system, its main protection is differential protection. The magnetizing inrush current caused by switch-in or recovery from external fault with voltage sudden rise, its magnitude is as same as which internal fault happens. The ability of identifying inrush current exactly is the focus of transformer protection at all times. At present, most of inrush identified methods based on Kirchhoff current law have the theoretic defect; some new theories and discrimination method, still wait for further consummation.With the development of power system, on-load tap changer transformers apply widely, therefore some coherent questions come up. Mismatch of TA secondary sides currents among these causes by taps changing, severely affect the accuracy and security of differential protection.Self-adaptive protection is able to identify and diagnose fault type automatically, then adjust fixed value and characteristic of protection. As the hardware base of adaptive protection, fast development of microcomputer system renders an extensive prospect for adaptive theory application.In this thesis, a new criterion based on voltage switching value compound with secondary harmonic restraint is put forward. A kind of TA currents correction method based on the analysis between TA secondary sides current and taps position is introduced, which can adjust TA secondary side currents online automatically.The simulation software PSCAD/EMTDC is used for evaluating the schemesuggested upside.