Elimination of Overshooting Effects and Suppression of Numerical Oscillations in Transformer Transient Calculations

This paper presents an original method of modeling nonlinear elements, particularly acceptable in the calculation of low-frequency transformer transients. A way of generating the state matrix coefficients is described. An algorithm is developed for state variable calculations based on the hyper stable backward differentiation formulas (BDF) BDFp, p-th order. The advantages of developing an algorithm which enables elimination of overshooting effect, as well as the suppression of numerical oscillations in low-frequency transformer transient calculations, are presented. Also, the reasons for the existence of overshooting effects and numerical oscillations are identified when the transformer transients are calculated in a nodal formulation of equations based on the trapezoidal method. It is shown that an implemented equation conversion procedure and/or a stiff system equation are indeed causing numerical oscillations in transformer transient calculations.