Intermediate Voltage Variation-Based Interconnecting Transformer Design for Voltage and Phase Angle Control With Coupled Field FEA Studies

A 160-MVA, 220/132/33-kV autotransformer is commonly used as an intermediate connecting transformer (ICT) in an electrical power transmission network. The modified design of such an ICT in order to get a phase angle control along with the voltage control, by intermediate voltage variation, is reported in this paper. Estimation of stray loss and core loss is done both by analytically and realizing 2-D and 3-D models by a finite-element analysis (FEA) method. A 3-D FEA design is further extended with arrangement of shunts to limit the stray loss and the thermal impact. Multiphysics simulation platform is used to link magnetostatic, steady-state thermal and structural FEA models. The composite FEA simulation approach used in this study enables steady-state thermal analysis of a transformer by importing stray loss from the magnetostatic model and the structural deformation in the transformer due to hot-spot temperature. To validate the proposed design, a 1-kVA, 415/230-V, three-phase transformer is designed, built, and tested in the laboratory. Voltage and phase angle at various operating conditions calculated analytically, obtained through FEA and measured experimentally, are in close agreement.