Recent Advances in Transformers in China

In recent years, the prices of core and conductive materials used in electronic transformers have risen steadily, creating a seller’s market for upstream raw materials. Meanwhile, downstream power‑supply users of electronic transformers enjoy the flexibility to source globally, resulting in a buyer’s market. Situated in the middle, the electronic transformer industry can only break free from this double‑edged predicament by pursuing technological innovation. However, in a mature sector like electronic transformers, driving innovation is challenging. Still, even minor improvements at each stage can give rise to fresh ideas and new products.

　　Pursuing technological innovation requires keeping the ultimate objective firmly in mind. Like all commercial products, electronic transformers used in power supplies must, under specific operating conditions and while fulfilling their intended functions, strive for the best possible performance‑to‑cost ratio. Today’s power‑supply products generally trend toward miniaturization and portability, characterized by being “lightweight, thin, short, and compact.” Consequently, electronic transformers must meet the size and weight requirements of the end‑user’s power‑supply applications. At the same time, the prices of raw materials—both core materials and conductive materials—are rising. As a result, reducing volume and weight while lowering costs has become the primary focus of electronic transformer development in recent years.

　　Silicon steel is the core material widely used in power-frequency electronic transformers. To reduce the amount of core material in such transformers, it is essential to increase the operating magnetic flux density (B‑value). The operating B‑value of silicon steel depends both on its saturation flux density and on its core losses. Since efficiency is a critical performance parameter for electronic transformers, many power‑supply products now impose stringent standby‑loss requirements to promote energy savings. Core losses account for the majority of standby losses; accordingly, strict and well‑defined limits are set for transformer efficiency or loss levels.

　　In recent years, prices for both grain-oriented and non‑grain‑oriented cold‑rolled silicon steel have risen. Compared with R‑type, CD‑type, and EI‑type cores, wound toroidal cores consume less material, reducing core‑material costs by more than 20% and thereby expanding their application in electronic transformers. Wound toroidal cores fully exploit the performance of grain‑oriented cold‑rolled silicon steel, achieving a significantly higher operating magnetic flux density than non‑grain‑oriented cold‑rolled steel. Moreover, unlike R‑, CD‑, and EI‑type cores, they make efficient use of silicon‑steel material, generating no edge‑cut scrap and attaining a material utilization rate exceeding 98%.

　　As a major category of electronic transformers, power-frequency transformers, when equipped with core materials featuring high magnetic flux density, can reduce the number of winding turns and copper usage without decreasing the core cross-sectional area or volume. Given that copper prices currently far exceed those of core materials, this approach may represent a more advantageous design improvement.