Research On Microchip-based Protection Of Large-scale Power Transformer

With the development of the power system, especially with the evolution of the modern material and new crafts, and the capability of power transformers becoming larger, the requirement for transformers protection becomes much stricter. Improvement of the performance of the transformers protection is depended on the extend that people know the transformers' inner faults. Study of the feature of inrush and internal faults of the transformers help to analyze the transformers' working state, improve the old protection's performance and develop the new protection scheme.The paper firstly introduces the present and future development of transformer protection. For the main problem, the discrimination of the inrush current, the methods current used is summarized roundly.An exact transformer model is the base of new theory's research, this dissertation explains how to simulate the transient process of excitation and internal fault of transformer used ATP. Base on the model, the factors affecting the inrush current are studied, especially the time when the breakers close. Two typical schemes of inrush current's discrimination, the second harmonic restraint principle and the correlation algorithm are analyzed thoroughly based on the dynamic simulation data, Their performance is compared, and the inner relation of the two principles is studied in the theory. Based on the study of differential principle in transformers protection thoroughly, the paper analyzed the comprehensive protection using both voltage and current and introduced several typical protection scheme. Considering the difficulty of the requirement of both sensitivity and reliability for differential protection, a scheme using the inner loss of the power is proposed. The scheme operates compatibly with the differential protection to form a comprehensive protection scheme, thus the requirement of sensitivity as well as reliability is both satisfied.