Study On Power Transformer Protection Novel Principle And High Speed Directinal Realy Algorithm Based On Power Quantity

With the wide use of the large capacity transformer, the importance of transformer primary protection performance is more apparent. So it is a thing with very vital significance to study the new transformer protection principle and algorithm with more excellent performance. The dissertation focuses on improving power transformer current longitudinal differential protection performance and researching the new transformer primary protection principle having nothing to do with the differential protection, the main content and the research results of the dissertation are as follows:(1) Based on the instantaneous reactive power theory, the dissertation proposes a new algorithm for discrimination between inrush current and internal fault current based on the ratio of real and reactive power of differential power. From the angle of energy conservation and the relationship between real and reactive power,the essential difference between transformer inrush current and fault status is revealed.(2) A computational method of excitation inductance of power transformer to identify inrush current has good effect. However the excitation inductance of power transformer with Y-Delta connection cannot be calculated directly using existed method because the winding currents on the Delta side cannot be measured based on existed TA configuration.An algorithm based on filtering zero sequence component to calculate the excitation inductance of power transformer with Y-Delta connection is proposed in the paper.The algorithm can calculate the excitation inductance representing the combined effects of both positive and negative components by using the delta side line currents directly.The results of the excitation inductance calculated using the algorithm proposed have distinct character in inrush current and fault condition,so the algorithm can identify inrush current effectively.(3) The dissertation proposes three high speed power directional protection algorithms and uses them in transformer protection.The proposed algorithm1is based on transformation of the instantaneous value symmetry component. The proposed algorithm2is based on the fundamental frequency positive sequence superimposed components. The proposed algorithm3is based on fault components with high-frequency transient quantities filtered out. The algorithm1uses the specially designed filters and fast filtering squence algorithms, and determines the fault direction by a novel fault direction criterion. Compared to algorithm1, the algorithm2and3need not the specially designed filters, and only use the conventional low-pass filter to filter the high-frequency transient quantities. The algorithm2presents a high speed algorithm for the extraction of fundamental frequency positive sequence voltages and currents superimposed components based on Park transformation. Be different to the high speed phasor algorithm of algorithm2,the algorithm3is a time domain high speed algorithm, and the current DC decaying component need not to be processed with additional method. In addition, a novel phase-sequence transformation matrix is constructed to identify faults for three-phase systems in the algorithm3, and sequence1quantity transformed by using this matrix is suitable for all fault types.The proposed high speed directional protection algorithms or principle can determinate the fault direction in short data window. With using the P level TA, the protection can reliably send out the clearing order before the TA saturation.(4) A transformer protection principle based on fault component reactive power directional element is proposed. The protection principle is based on fault component protection principle. Only collecting voltage and current data of the transformer port and without any transformer internal parameter, the principle is simple and highly reliable, independent of inrush current, suitable for the differently connected transformers,and can distinguish any operation state including inrush current produced by energizing with load and external fault clearing,and has good project application prospect.(5) The dissertation proposes a novel transformer protection principle using fundamental frequency positive sequence power factor to effectively distinguish between switching the transformer with an internal fault and inrush current. By using the Park transformation,the fundamental frequency positive sequence power factors of transformer in various transient process are obtained.According to the fundamental frequency positive sequence power factor of transformer, magnetizing inrush and internal fault can be distinguished. The principle has clear physics significance, easy engineering realization,and need not any transformer internal parameters,and is free from the impact of transformer wind connection mode,has sufficient sensitivity for energizing into light turn-to-turn fault.