Frequency domain transformer model for electromagnetic transient analysis of networks

In this paper a frequency domain three-phase transformer model is implemented using a nodal approach. Easiness and effectiveness of the model are demonstrated by its inclusion in a simplified distribution network. Moreover, angular displacement inherent to different connections of windings is taken into account which proves its versatility. Transient overvoltages caused by switching are computed using the model and the time domain response is obtained using the Numerical Laplace Transform (NLT). Results are assessed by comparisons with EMTP-RV.

I. Introduction

Transformers are essential elements of electrical power systems. For that reason, their accurate modeling and inclusion in electrical network simulations have always been a subject of great interest (see for instance [1], [2]). Frequency domain (FD) methods are a good alternative to time domain (TD) methods for the simulation of electromagnetic transients since the modeling of components and networks can be accomplished by means of simple algebraic equations, in contrast to the integro-differential equations required in time domain. In addition, the inclusion of frequency dependent parameters does not require from the numerical approximations needed in TD methods; this contributes to the high accuracy of FD methods. Although the application of such methods has been commonly regarded as restricted to the study of linear networks without changes in their topology, it has been demonstrated that the inclusion of switching conditions and non-linear elements is possible via the principle of superposition and piece-wise linear approximations [3].