Magnetic Properties of Simultaneously Excited Amorphous and Silicon Steel Hybrid-Cores for Higher-Efficiency Distribution Transformers.

摘要

Amorphous core transformers (AMT) have the major advantage of higher power efficiency due to lower iron loss (W_i) compared with that of grain-oriented silicon steel (GO) cores used in conventional transformers (SiT) ^{[1]. Some studies have attempted to increase the power capacity of AMTs to over 5 MVA [2]. However, the enlarged amorphous core, made from stacked foils 25-mm thick, is vulnerable; it requires structures to support its weight. Additionally, the saturated magnetic flux density (B_S) and the lamination factor of the amorphous core are approximately 18% and 10% lower, respectively, than those of the GO core. This results in the amorphous core having a larger cross-sectional area than that of the GO core with same the specifications. To enable the use of an amorphous core with lower W_i in large capacity distribution transformers, we investigated the practicality of a hybrid-configured annular core consisting of an amorphous core combined with a GO core, which has the advantages of a higher B_S, lamination factor, and mechanical strength than the amorphous core. The distributions of the magnetic flux density and W_i in the hybrid core were measured and calculated with electromagnetic analysis using the three-dimensional finite element method (FEM) while the two individual cores, amorphous and GO, were excited simultaneously. We then designed a prototype 5-MVA single-phase hybrid core transformer (HBT) on the basis of our investigation results. The prototype had improved power efficiency due to its lower W_i and reduced size enabled by the increased amplitude of magnetic flux density, B_m.}