Large Transformer Protection Based On The Transient Variable

Large power transformer is the vital important electric installation in electric system. With the development of national economy, required quantity of large transformers is getting large. Whether large transformer operating normal or not has direct relation to electric system , which will work series,normal and stabilize . Large power transformer is expensive, and it needs operating well. Once large transformer broken, it is hard to be repaired within long times, which will make big economic loss. In recent years, the scale of electric system is getting up, and the level of voltage is getting high .The accidents of large transformer are increasing when more large transformers brought into action .It demands high claim of rapidity and reliability in transformer protection .Thus to search preferable large transformer protection method has momentous sense.This dissertation analyses the electromagnetic property of the large transformer, and proposes a transformer protection method based on two transient variables. Using the increment of flux linkages by current and voltage, it can distinguish excitation current from internal fault current .The emulation under MATLAB environment indicates that the method on identification of excitation currents is reliable. Taking DSP as the inside core, backstage software controls the act of the protection equipments by the sampling signal which flows from DSP to photoelectrical insulation. Thus the large transformer protection achieves. The results of the experiment indicate that the new method can distinguish internal fault current from magnetic inrush effective and dependable.