Iron losses and acoustic noises of the model transformer under DC-biased magnetization were empirically investigated. To clarify the influence of magnetic properties of transformer core materials, two types of grain oriented electrical steels—high permeability grade (HGO) and conventional grade (CGO)—were used as core materials. Iron losses increased with superimposing DC-bias magnetic field (HDC) in both materials, and the iron loss increment in HGO was larger than that in CGO. Acoustic noises increased with increasing HDC in both materials; however, noises emitted from the core of HGO were smaller than those of CGO.
The iron losses and acoustic noises of a model transformer core made of grain-oriented electrical steel sheets were investigated under DC biased magnetization while altering the amplitude of magnetic flux density, Bm, and the DC biased magnetic field, HDC, applied by the third windings. The iron loss increased as HDC increased up to 100 A/m, while over 100 A/m, the increment of iron loss by DC biased field rapidly decreased. The increase in iron loss at the same HDC was largest at Bm:1.1-1.5 T. Meanwhile, the acoustic noise increased monotonically as HDC increased. The acoustic noise of odd-order harmonics was drastically increased under DC biased magnetization, and this is the primary cause of the increase in acoustic noise.
A three-legged wound transformer core is composed of two inner cores and one outer core, and the interlaminar flux occurs between inner and outer cores in three-phase excitations. Past analyses of magnetic properties of three-legged wound transformer cores were based on the model of independent magnetic paths in the individual core, and did not factor the influence of interlaminar flux in the calculations. This paper shows experimental results of interlaminar flux between cores and iron loss increase caused by that. Results show that the interlaminar flux between the inner and outer core increases the local iron loss in the boundary region of the inner and outer core.
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