EFFECTS OF DC-BIAS ON LOSS DISTRIBUTION OF MODEL TRANSFORMER CORE
Helmut Pfützner – Georgi Shilyashki – Franz Hofbauer – Damir Sabic – Edin Mulasalihovic – Viktor Galabov
By means of the rise-of-temperature method, the regional distribution of the local building factor BF was measured at 23 positions in a model transformer core assembled from grain oriented SiFe. In a systematic way, the case of mere AC excitation was compared with that of additional DC excitation in the middle S-limb. The mere AC case showed lowest BF in the central regions of the outer limbs, highest one in the corners and – in special – in the T-joints due to rotational magnetization (RM). DC bias yielded strongly increased BF in regions of alternating magnetization and lower ones in regions of RM, a tendency which is interpreted through domain theory. Energetic relevance is not expected for the case of geomagnetically induced currents, strong effects being restricted in time. On the other hand side, weak bias of long term may deteriorate the performance of 5-limb 3-phase cores and – in special – that of 1-phase cores.
Keywords: transformer cores, magnetic losses, DC bias, magnetic domains, energy problems