Three-phase timing-domain modeling of special transformers in the zyx MLK SABER simulator zy ON Elder G. Domingues, Jod C. Oliveira, Antonio C. Delaiba, Anderson L. A. Vilap, Milton zyxwvut KJIHGFE 1. Samesima (Member), Jod Wilson Resende, Jod Rubens Macedo Jr. Federal University of Uberlandia zyxwv FEDC - Brazil e-mail: samesima@ufb.br Abstract: This paper presents a general three-phase model for Wye/I.)eIta-extended transfonners for time- domain analysis. Among other features, the modeling includes the non-linearities of the core the transformer phase-shifting can be of any value. The model is implemented in the SABER simulator and tested in a 24-pulse converter. The corresponding results are presented and special attention is given to h elimination and inrush currents. Key-words: special power transformers, non-linear modeling, electrical power systems. 1. INTRODUCTION The Wye-Delta-extended transformer type is to be adopted in the 500 zyxwvut HGFED MW 12 pulse converter station, located in Vindhyacal (India) [I]. Among other advantages of this type of connection, reference [I] shows that, for the same DC load power to be feed, the Wye-Delta- extended transformer zyxwvuts EDCBA can be of smaller apparent power than a conventional wye-delta transfomer. This transformer connection is a special arrangement which provides non-conventional phase shifting angles for three-phase transformers. For instance, phase-shifting of zyxwv KJIHGF 0". IS", 30", 45" and 60" can be easily obtained. This feature, therefore, can be useful in multi- converter stations, as far as harmonic elimination is bncemed [2]. Figure 1 shows a general primary/mndary transformer arrangement, which is useful to understand the Wye-Delta- extended concept. The number of spires of th6 secondary, x and y, zyxwvutsr A can be evaluated through the triangle sine law. The final results are in equations ( I ) and (2). zyxwvutsr EDCBA sin(60' - 8) -sine N , sin1 20' where: K N = K F I V W VIP = primary voltage per phase; VzF = secondary voltage per phase. 2. SATURATION EFFECTS It is well established that if the operation point of a transformer is in the linear region of the magnetization curve, then the voltages and magnetic fluxes wavefmns are purely sinusoidal. This leads to a inductance of constant magnetization. However, this is no longer true if the magnetic saturation effect is also taken into account. That this, in this case the voltages and magnetic fluxeswaveforms are no longer In order to introduce the magnetic saturation effect, it is essential to know the magnetization characteristic (€3 x H curve ) of the transformer, such as in figure 2. The magnetization current can be evaluated from this . - - . - sinusoidal. *T NI p I e Figure 1 - Wye-Delta-extended transformer "e. windings 0-7803-5105-3/98/$10.00 0 1998 IEEE 1047