An improved method for virtual air gap length computation

This paper presents an analytical approach to the analysis of a single-phase transformer with a virtual air gap. Four auxiliary windings with dc currents that locally saturate the core are embedded in the transformer core. Due to changes in the magnetic characteristics of the core a virtual air gap is created. The method focuses on the change in transformer core reluctance with local saturation and on obtaining the equivalent mechanical length of the virtual air gap. The accurate calculation of the magnetic field in the core is necessary to obtain both the operating point of the core and the change in core reluctance. Results obtained from the proposed method are compared with experimental and analysis results available in the literature.