Abstract: The grain-oriented silicon steel, once being processed into transformer core, has a direct impact on power network’s energy use and safety. This paper provides a thorough evaluation of the properties of used silicon steel. Our results show that serious product quality issues exist with used silicon steel sheet. For sample sheets from three regions of A, B and C, the highest core loss (P1.7) was 1.91 W/kg (high no load losses), the highest magnetostrictive coefficient (λ1.7T) was 3.9×10-6 (high noise), the lowest surface insulation resistance was only 1~2 Ω·cm2 per sheet(low insulation between sheets is a direct threat on the safety of the steel core), and the coating adhesive property was at D level or worse. The sustained use of used silicon steel in grid connected transformers presents a serious quality and safety concern. Whether or not the transformer core was made from used silicon steel can be determined through a comprehensive inspection of the surface quality, magnetic performance, coating property and microstructure of the silicon steel sheet.

Key words: distribution transformer, grain-oriented silicon steel, performance evaluation, inspection