Study Of Transformer Protection And Device Based On Differfntial Protection Principle

With the development of power system, especially with the evolution of the modern material, new crafts and the larger capability of power transformers, the requirement for transformers protection becomes much stricter. Study of the features of inrush and internal faults of the transformers can help to analyze the transformers' operation state, to improve existed protection performance and to develop new protection schemes. In this paper, the research of discrimination of the excitation inrush current is analyzed. The four-ratio restrain criterion is studied through the simulation of the current transducers saturation. This paper firstly summarize the present and future development trends of transformers protection and then the principle of longitudinal differential protection. Both the cause and the elimination of the unbalanced current are analyzed. The study and comparison of the excitation inrush current are mainly analyzed. Ratio-restrained differential protection is a main approach to prevent the mal-operation of the transformer when external faults happen. This protection is influenced by transient error that is caused by the current transducers saturation. The model of inductor is conceived, from which we acquire the change of current when applied to different types of external faults. A four-ratio restraint criterion is proposed. In comparing with the three-ratio restraint criterion, the simulation results reveal that four-ratio restrain criterion can improve the delicacy of longitudinal differential protection. In the end, a protection scheme that is applicable to the 110kV transformer is proposed, while its hardware structure and protection device are analyzed.