Electrical modeling of transformer connecting bars

Abstract

Traditionally, connections in high-voltage, high-current, and low-frequency circuits are always considered as perfect short circuits, so to analyze their contribution to electrical performance of a structure is not considered necessary. We show here that, even for low-frequency structures, the electrical parasitic characteristics of cabling can lead to some unexpected performances. In particular, our study of outside connections of a 400 MVA transformer has shown current unbalances between the three phases and inside the phases. We achieved this by using a semianalytical method that is presented in this paper. Results show the need to model this part of the structure. This method has advantages over numerical techniques of calculation.Index Terms-Electrical modeling, parasitic inductance of connections, PEEC method.

Analytical Calculation of Static Leakage Inductances of HF Transformers Using PEEC Formulas

“…However, this potential is among the more widely involved by the PEEC method [5], [6], except that source wire is assumed here to be infinitely long. Rectangular components of induction (6) and (7) are deduced from the vector potential (5) through proper derivatives.…”

“…Generally, two to five "wires," each accounting for a winding or a part of a winding, lead to accurate values. Obviously, this approach relies on the same basic formulas as partial-element-equivalentcircuit (PEEC) method [5], [6] does. The weak magneticcore effect is also taken into account, by adding one or eight magnetic images of the windings.…”

Numerical Method of Computing Impedances in Shielded and Unshielded Three-Phase Rectangular Busbar Systems

“…In this model, each phase, neutral busbars and each plate of the enclosure are divided into several thin subbars [6,8,17,23,35,37], as shown in Fig. 3.…”

“…Also, in a high-current bus duct, where the phase busbars are connected in parallel, their impedances can cause unbalances in the total current sharing. And according to the unbalance level, over-loaded parts can lead to a heating of the structure at some points, or can be damaged by electrodynamic efforts [8].…”

“…These impedances can also be determined by experimental methods [41][42][43][44]. According to [9], the capacitances in the three-phase high-current bus duct systems are below 20 nF/m, and at the industrial frequency f = 50 Hz they are usually neglected [1][2][3][4][6][7][8][9][10][11]. We also neglect them, because for the bus ducts considered in this paper we found the approximate values of capacitances to be about 20 pF/m (using FEMM).…”