Eddy Currents in Magnetic Cores and Laminations
Magnetic core materials, like silicon steel used in power transformers, are conductive, allowing the magnetic field to induce eddy currents within the material. These eddy currents lead to heating, necessitating measures to limit them. Power transformer cores are commonly constructed from stacked laminations—thin layers of magnetic material—arranged in shapes such as E-I, E-E, D-I, or L-L. The laminations are interlaced and coated with insulating material, preventing the core from appearing as a solid conductive block. This stacking method introduces gaps at the E-I interfaces, preventing eddy currents from flowing between laminations.
Audio transformers, requiring functionality across a broad frequency range, have core sizes related to lower-frequency voltages. Since flux swings at higher frequencies are minimal, lamination thickness doesn’t need to accommodate high-frequency losses. While solid-state circuitry has replaced many audio transformers, some higher-end equipment still uses them for the distinctive tone quality they provide.
Power distribution transformers, especially those dealing with electronic loads high in harmonic content, are often rated with a “k factor” to account for increased transformer core and copper losses. The k factor must be sufficiently high to prevent overheating caused by these loads. Despite advancements in technology, the unique characteristics of transformers still find applications in specific scenarios where their performance is valued.