The single-phase distribution transformer consists of a primary winding and a secondary winding wound in a _____________ core.

• A. Laminated Paper
• B. Porcelain
• C. Polycarbonate
• D. Laminated Steel

Answer: (D)

Magnetic cores for distribution transformers must provide a low-reluctance path for flux while keeping losses down. A laminated steel core achieves this because steel has high permeability, so magnetic flux can pass with less resistance. Laminating the steel—insulating between thin sheets—limits eddy currents to small loops within each sheet, drastically reducing eddy current losses and heating. Silicon steel laminations are commonly used to also reduce hysteresis losses and improve overall efficiency. The other materials wouldn’t form an effective magnetic path: laminated paper doesn’t carry magnetic flux well, porcelain and polycarbonate are insulators or structural materials, not suitable for the magnetic core. Therefore, the appropriate core material is laminated steel.