Power Transformer Protection Research Based On Transient

Power transformers are most important equipments in power plants and power substations, they have a great influence on the secure operation of power system. With the development of power system and the application of modern materials, the power capacity of transformers becomes bigger and bigger, and the requirement to improve the performance of transformer protection relay is getting stronger. Whether the performance can be improved depends on the extent to which people realize the mechanism and feature during magnetic inrush and faults. So the transient simulation is pretty necessary.One of the key problems during the transient simulation is to simulate the hysteresis loop. Based on the special quality of ferromagnetic material, the author builds a transformer simulation model. And grounded on it, we discuss the influence on hysteresis loop of such factors as the material, the setup of magnetic path parameters, the structure of magnetic path, and so on. Of all the kinds of transformer faults, the turn-to-turn fault and turn-to-earth fault are the most frequent. Based on the available achievements of other scholars, we build a model with which all the turn-to-turn and turn-to-earth faults can be simulated wherever it takes place, and at the same time, all the other kinds of faults can be simulated with it.One effective approach to improve the performance of transformer protection relay is to apply new theory and new technique. Wavelet analysis, a new method which develops very fast these years, has the properties such as the multi-resolution analysis and localization characteristic in both the time domain and the frequency domain. It specializes in the character acquirement of fringes and abrupt signals. The wavelet analysis theory and its application in power system are introduced briefly in the thesis. And a new method is proposed based on the wavelet analysis theory by which the transformer internal faults can be detected, the internal and external faults can be differentiated. Specially, the inrush currents after both the external faults are removed and no-load closing, internal fault during the closing without load and internal fault during the closing with load on can be distinguished.The theoretical analysis and simulation results demonstrate that the above-mentioned algorithm is effective even if the Current Transformers (CTs) are saturated.