Circuit Reduction Techniques in Multiphase Modelling of Power Transformers

Multiphase transmission line representations are used in the high-frequency modelling of transformer windings for the estimation of fast overvoltages as well as in the analysis of diagnostic methods used in condition monitoring. Due to the large dense matrix representations of these systems, simulation of turn-by-turn models are prohibitively computationally expensive. Consequently, various techniques have become common in reducing the system size. This paper compares five such techniques: reduction to capacitive system, single transmission line (STL) equivalent, multiphase STL, hybrid transmission line preserving total inductance and the hybrid transmission line preserving TEM mode of propagation. The results indicate the hybrid transmission line preserving the total inductance of the system is the most accurate especially as the number of turns being modelled increases.