Circulating currents that cause unwanted heating in a transformer are called what?

• A. Eddy currents
• B. Thermal currents
• C. Magnetic currents
• D. Surface currents

Answer: (A)

Circulating currents in a transformer caused by a changing magnetic field are called eddy currents. When the magnetic flux in the core changes with every AC cycle, electric fields are induced inside the conducting metal. These fields drive small loop currents that swirl through the material rather than following the intended circuit paths. As these loops carry current, they dissipate power as heat (I^2R losses), leading to unwanted heating and reduced efficiency. To minimize them, the core is made of thin, insulated laminations; the insulation between laminations disrupts large loop formation and confines currents to smaller paths, cutting the heating. The other terms don’t fit this well-known phenomenon: they aren’t standard names for these induced circulating loops in transformer metal.