Abstract: Quality supervision and evaluation were conducted on the grian-oriented (GO) silicon steel used for power transformers/reactors in the 220-1 000 kV substation project newly built and expanded by State Grid Corporation of China from 2020 to 2023. A total of 175 substation projects, 24 transformer manufacturing enterprises, and 3 GO steel production enterprises were involved. Based on the technical conditions and testing method standards of GO steels, over 20 000 pieces of GO steel samples, including 23 grades such as 20QH070, 23QH075, 27QH085, and 30QH100, were randomly inspected. Overall, the failure rate of performance has been decreasing year by year, and the problems in magnetic properties, coating performance, and appearance quality of batch supplied GO steels have been identified. By continuously conducting quality assessments of GO steels, we have provided strong support for strengthening the source control of power transformer quality and helping to build an inherently safe power grid. 

Key words: power transformer, grain-oriented silicon steel, quality assessment, source control