Maximum power is limited by thermal and insulation constraints rather than just kVA math. At rated voltage and frequency, winding and core losses create heat; the transformer can only dissipate so much before insulation ages rapidly. Cooling class, ambient temperature, hot-spot temperature limits, and insulation class define how much current can safely flow. Short-term overload curves allow temporary higher loading, but continuous power must keep temperatures within design limits to avoid accelerating aging or triggering protective relays.