The power rating of a transformer describes how much apparent power (kVA or MVA) it can continuously deliver without exceeding thermal limits. It depends on conductor size, core cross-section, insulation class, cooling system, and allowable temperature rise. The rating ensures that both copper losses and core losses remain within design limits under nominal voltage and frequency. In power systems, ratings are often expressed in MVA to reflect the role of transformers in transferring apparent power between voltage levels without changing total system power.