Inside a power transformer you find the magnetic core, primary and secondary windings, insulation systems (paper, pressboard, spacers), clamping structures, core/coil assembly supports, oil channels or ducts, and, in oil-filled units, the insulating liquid itself. Bushings connect windings to external circuits, while internal leads route current to tap changers. Many designs include temperature sensors, winding supports, and internal shields to control electrical stress and stray flux. Each component is selected to withstand electrical, thermal, and mechanical stresses over decades.