Time-Stepping Finite Element Analysis of Distribution Transformers Performance under Unbalanced Voltage and Load

Abstract

In this article, a distribution transformer is analyzed under unbalanced voltage and unbalanced load. The transformer is modeled using the time-stepping finite element method, considering all geometrical and physical characteristics. To analyze precisely the occurrence of unbalanced voltage and load in transformer, spectral analysis of the secondary current is essential. To this, the frequency spectrum of the secondary current, obtained using the time-stepping finite element method, is calculated. It is shown that the unbalanced voltage or unbalanced load in the distribution transformer adds to the amplitude of harmonic components considerably; however, its incremental rate has a decreasing pattern. The amplitude of the harmonic components for the two unbalanced cases are compared, and it is shown that the unbalanced voltage has more effect upon the increase of the amplitude of the harmonic components compared to the unbalanced load. Meanwhile, the performance of the distribution transformer under balanced and unbalanced voltage and load is studied. The performance of the transformer when the load and supply are balanced compared to the case in which voltage or load is unbalanced indicates that the unbalanced load only causes the copper loss to increase, while the unbalanced voltage not only increases copper loss but also adds to the core loss. It is also shown that unbalanced voltage increases the copper loss more than an unbalanced load. Simulation results are verified by experimental results.