A Calculation Method to Adjust the Short-Circuit Impedance of a Transformer

Abstract

A staggered transformer of power frequency inverters in uninterruptible power supplies (UPS) can be used as both a voltage transformer and an inductance of filter circuits to replace a traditional reactor. In this paper, a method is presented to calculate the short-circuit impedance $Z_{\mathrm {k}}$ of a staggered transformer. which can be adjusted by using different arrangements of primary and secondary windings. Using the structure parameters of core and winding and the magnetic circuit analysis method, the proposed method in this paper can accurately calculate $Z_{\mathrm {k}}$. This high-precision and simple formula is easy to apply in engineering. First, a model of the single-phase isolation transformer (the winding arrangement is PSSPPS) is established using FLUX 3D and verified by comparing the simulated data with the measured data. Second, short-circuit impedances of four typical winding arrangements (PSSPPS, SPSPPS, PSPSPS, PPPSSS) are obtained by simulation. The results show that the errors between the simulation and calculation are less than 10%, which proves the validity of the method. Finally, an analysis of the magnetic field parameters of the staggered transformers with different winding structures shows that the number of parallel branches of leakage flux magnetic circuits increases with the complexity of the winding structure, which is consistent with the theory.