Effects of Numerical Oscillation in Switching of Power Transformer Connected To A Power Network

Abstract

This thesis presents a method of modeling nonlinear elements, particularly acceptable in the calculation of low-frequency transformer transients. A program is developed for various variables calculations based on iterations. The development of an accurate transformer model can be very complex due to the large number of core designs and to the fact that several transformer parameters are both nonlinear and frequency dependent. Physical attributes whose behavior may need to be correctly represented are core and coil configurations, self- and mutual inductances between coils, leakage fluxes, skin effect and proximity effect in coils, magnetic core saturation, hysteresis and eddy current losses in core, and capacitive effects The advantages of developing an algorithm which enables study of numerical oscillations in low-frequency transformer transient calculations, are presented. Also, the reasons for the existence of numerical oscillations are identified when the transformer transients are calculated in formulation of equations. The transformer model can be easily interfaced with an electromagnetic transients program. Its main features are: (a) the basic elements for the winding model are the turns, (b) the complete model includes the resistances, inductances, impedances, permittivity and current in the windings, the iron core and the overhead line (c) the solution of the equations is obtained by developing programs and solving the various values and subsequently plotting those values using iterations.