Transformers at power line substations adjust voltage levels between transmission and distribution tiers. Step-down units reduce high transmission voltages (e.g., 110-400 kV) to medium voltages for feeders, while auxiliary transformers supply station loads. Their purpose is efficient long-distance transfer of power with minimal losses, impedance matching between network levels, and system protection coordination. Tap changers provide voltage regulation, while cooling systems maintain thermal stability under fluctuating grid loads.