Prediction of no-load losses of stacked 3-phase, 3-limb transformer cores

The work presented in this thesis can be utilised by electrical steel manufacturers and transformer designers to design energy efficient transformer cores possessing lower life cycle costs, thereby increasing financial gains. A novel computer based algorithm to predict losses of 3-phase, 3-limb transformer cores built with high permeability grain oriented steel (HGO) and conventional grain oriented steel (CGO) is presented. The algorithm utilises parameters like transformer geometry, global flux distribution, localised loss data and material properties thus enhancing the accuracy of the predicted results which were 1% of the measured values. This algorithm has contributed to new knowledge in the no-load loss prediction approach. Six, geometrically identical, 350 kVA stacked five packet 3-phase, 3-limb transformer cores assembled with HGO, CGO and four mixed combinations of HGO and CGO laminations in multi step lap (MSL) joint configuration were tested for the global flux density distribution and no-load loss. The investigation results are novel and suggest that the bolt hole diameter (slot width) and lamination width ratio affects the packet to packet variation of . This is a new contribution to the flux distribution regime in transformer cores. The no-load loss experimental results are novel and suggest that the variation of no-load losses with CGO content in mixed cores was non-linear because of the packet to packet variation of . This is a new contribution of knowledge in the field of mixed core loss behaviour. Novel data sets of localised specific loss increase and localised relative permeability decrease around different sizes of holes and slots for HGO and CGO were processed from data obtained by two dimensional finite element (FE) analysis. The data sets are a new contribution in the field of predicting localised magnetic properties around holes and slots