Study On Simulation Model And Protective Schemes For Transformer

Transformer is the hinge to transform electric energy in different voltage. It is one of the most important major apparatuses in the power system. Its running state will restrict the safety and stability of the power system. Transformer is a quite costly major apparatuses, which price is high and should be set corresponding protection. Recently, the correct operation percentage of transformer protection is relative low, which is far less than the line protection's and generator protection's. Some unknown reasons may cause transformer protection to misoperate. The existing transformer protections haven't filled the demand of the power system. On the integration of theory and practice, this paper has study some relative problems to transformer protection and performed some research works as below:(1) A transformer model for simulating internal fault has been built. To simulate the tum-to-earth or turn-to-tum fault in the transformer, the transformer fault winding is divided to two or three windings. According to the transformer flux paths and transformer magnetic equivalent circuit, using the modeling theory of Unified Magnetic Equivalent Circuit (UMEC), a transformer model for simulating internal fault has been presented, in which the necessity to input detailed core data such as the lengths and the cross-sectional areas of each limb, and the actual number of turns in each winding has been eliminated. Without considering the saturation of the limb, the model may be used for analyzing the transformer fault and calculating the fault current. By simulating the hysteresis characteristic of the transformer limbs using JA theory, the model may simulate the operating condition when energizing no-load transformer with internal fault.(2) Several novel criteria to identify inrush current are presented. It is well known that inrush current has the characteristic of dead angle and tip wave, compared with which the fault current is near to sine wave. By contrasting the calculated result of full-cycle fourier algorithm with the calculated result of half-cycle fourier algorithm, it is known that the calculated result of half-cycle fourier algorithm can reflect the characteristics of the inrush current. Based on the half-cycle fourier algorithm, according to...