Transformers chiếm vị trí nổi bật trong hệ thống điện, là các liên kết quan trọng giữa các trạm phát điện và các điểm sử dụng. Biến áp là một thiết bị chuyển đổi điện từ năng lượng điện nhận được (X0/X1 không | 3 Impedance Characteristics The leakage impedance of a transformer is one of the most important specifications that has significant impact on its overall design. Leakage impedance which consists of resistive and reactive components has been introduced and explained in Chapter 1. This chapter focuses on the reactive component leakage reactance whereas Chapters 4 and 5 deal with the resistive component. The load loss and hence the effective AC resistance and leakage impedance are derived from the results of short circuit test. The leakage reactance is then calculated from the impedance and resistance Section of Chapter 1 . Since the resistance of a transformer is generally quite less as compared to its reactance the latter is almost equal to the leakage impedance. Material cost of the transformer varies with the change in specified impedance value. Generally a particular value of impedance results into a minimum transformer cost. It will be expensive to design the transformer with impedance below or above this value. If the impedance is too low short circuit currents and forces are quite high which necessitate use of lower current density thereby increasing the material content. On the other hand if the impedance required is too high it increases the eddy loss in windings and stray loss in structural parts appreciably resulting into much higher load loss and winding oil temperature rise which again will force the designer to increase the copper content and or use extra cooling arrangement. The percentage impedance which is specified by transformer users can be as low as 2 for small distribution transformers and as high as 20 for large power transformers. Impedance values outside this range are generally specified for special applications. 77 Copyright 2004 by Marcel Dekker Inc. 78 Chapter 3 Figure Leakage field in a transformer Reactance Calculation Concentric primary and secondary windings Transformer is a three-dimensional electromagnetic .
