Research On Some Problems In Simulation Of Power Transformer Inrush Current

This paper studies on some problems of power transformer inrush current, presents a new method to calculate magnetization curve, and prompts kinds of approaches for computing leakage inductance and excitation inductance used in novel principles of power transformer protection.For the strictly requirements in security and limitations of new protection methods , differential protection method, which is considered to be simple and sensitive , is still extensively used in the power protection field. Inrush current discrimination is one of the most important factors that influence protection performance. After the concept of inrush current is introduced, the existing methods for discriminating inrush are discussed.Inrush current discrimination bases on the magnetization curve of a certain transformer, and the form of magnetization curve effects the calculation of inrush and harmonic components. A new piecewise linearized approach, which takes account of iron core losses and bases on the transformer test data provided by the manufacturer, is presented for the computation of the saturation characteristics iron cores, and has obvious advantages over others. The accuracy can be easily controlled.Distinguishing magnetizing inrush currents from internal faults can be effectively fulfilled by using the criterion of an instantaneous excitation inductance and an equivalent instantaneous inductance, which is based on the difference of the magnetic permeability in iron core of transformer between inrush currents and internal fault. Recent years, there are two novel principles have been proposed basing on leakage inductance parameters vary obviously during internal faults. All of these methods require calculation of inductance parameters. Therefore, some advanced computational methods are proposed in this paper. The results of experimental tests show that these proposed methods are correct and effective.There are four chapters in main body. Chapter 2 introduces the concept and discrimination methods of inrush current; Chapter 3 presents a novel approach for computing magnetization curve; Chapter 4 describes how to calculate leakage and excitation inductances; In reviews of the protection means, Chapter 5 gives the prospective protection methods.