Abstract: The development of S15 type ultrahigh energy efficiency transformer based on low loss grainoriented (GO) silicon steel is of great significance for further promoting energy saving and efficiency enhancing of power grid. The magnetic properties and magnetostrictive characteristics of 0.18 mm GO steel, 1K101-S and 1K102-P amorphous alloy were studied using measurement system under arbitrary waveform of magnetic induction. The core losses of 0.18 mm GO steel under harmonic and DCbias were analyzed, and the modeling and simulation analysis of iron core as well as winding of S15 type transformer were carried out by using the MagNet finite element software. When the magnetic flux density is 1.35 T, the core loss of 18QH065 GO steel is as low as 0.349 W/kg, which is approach to the level of amorphous alloy. The magnetic induction B800 of GO steel is 0.32-0.40 T higher than that of amorphous alloy strip. The magnetostrictive coefficient of GO silicon steel is 0.29×10-6, which is lower than that of amorphous alloy by one order of magnitude. Besides, the harmonic loss of 0.18 mm silicon steel is significantly lower than that of 0.23-0.30 mm silicon steels, and the third and fifth harmonic losses under content of 10 % increased by 12.9 % and 16.0 % respectively. DC bias (0-150 A/m) has an obvious effect on the core loss of 0.18 mm GO steel under low magnetic flux density (MFD), while the loss is almost the same after MFD higher than 1.9 T. Finally, the noload loss of designed 10 kV/630 kVA transformer is 392.5 W (31.1 % lower than that of transformer with firstgrade energy efficiency in standard of GB 20052-2013), and the noise is about 10 dB lower than that of amorphous alloy transformer with the same capacity, which means significant advantages of energy conservation and environmental protection.

Key words: ultra-low power loss, grain-oriented silicon steel, simulation analysis, ultra-high energy efficiency