Study On The Improvement Ways Of Power Transformer Differential Protection

Power transformer is essential and important element of power system. It plays an important role in the power supply system. The reliability of power transformer directly determines whether the power system works safely or not. Especially for extra high voltage transformer is expensive, great economic benefits would be lost as a result of the fault of power transformer. Differential protection is the master protection for transformers all along. There are many problems need to solve. The transformer differential protection is not sensitivity to the turn-to-turn circles short and identification of the fault current with inrush current is also the problem that cannot be evaded. Based on the integrated protection, there is great important meaning in the improvement of transformer protection level and improving of existed transformer differential protection.This paper analyzes the problems about the differential protection, and appraises various ways of distinguishing methods. Use the simulating software EMTDC to make the transformer model which can simulate integrally internal fault of transformer and the magnetic inrash current. The simulation model is proved effective by comparing the waveform with dynamic simulation experiments. It is a feasible way to get the data of research which is useful to the following research. At the same time, the influence of tap change to unbalance current is studied. Two advanced methods for improving the sensitivity of the digital differential protection is presented in this paper. The new approaches based on adaptive adjustment of the percentage differential protection takes into account the tap position of the power transformer with on-load tap changer. The digital differential protection can be more sensitive to the faults of transformer by reducing the unbalance current caused by the tap changing.By studying the algorithm of equivalent instantaneous inductance scheme for wye-delta connected transformer, it finds that it limited the application based on the equivalent instantaneous inductance scheme to identify the inrush according to the circulating current in delta winding. Because the circulating current in delta winding is not easily measurable, this paper using the advantages of integrated protection constructs a algorithm to obtain the circulating current based on the transformer mode loop equations. It can obtain accurate circulation when the internal turn to turn short fault happens, which is maintaining good accuracy and a wide range of applicability. At last, program the transformer differential protection and provide a experimental platform to the integrated protection for the practical applications.