The laminations used in the core are made of which material?

• A. Grain-Oriented Silicon Steel
• B. Pure Copper
• C. Aluminum
• D. Stainless Steel

Answer: (A)

Lamination material in transformer cores is chosen to minimize energy losses from the changing magnetic field. The material needs high magnetic permeability to carry flux efficiently and high electrical resistivity to keep eddy currents small. Grain-oriented silicon steel fits this need: adding silicon increases resistivity and reduces hysteresis losses, and the grains are aligned to maximize magnetic properties in the direction of the flux. Thin sheets, insulated from one another, further suppress eddy currents by breaking conductive loops between laminations. Pure copper or aluminum would conduct too readily, causing large eddy currents; stainless steel has poorer magnetic properties and higher losses. So the laminations are made of grain-oriented silicon steel.