1. Maximum Winding Temperature Above Ambient at Rated Load This rating is the highest temperature rise of transformer windings above the surrounding ambient temperature when operating at rated load. •
Rated Load is the maximum continuous load (in kVA) that the transformer is designed to handle under standard conditions without exceeding temperature limits.
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Typical Limits o
Average winding rise: 65°C above ambient Hot-spot rise: 85°C above ambient Ambient temperature design is typically 30°C
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Standard Conditions o
Within designed cooling method parameters
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Total Hot-Spot Temperature permissible is Ambient (30°C) + Hot-spot rise (85°C) = 115°C maximum Standard Reference is IEEE C57.12.00 and C57.12.90 for liquid-filled transformers. Higher temperatures accelerate insulation aging Maintaining limits ensures expected service life and reliability under normal operating conditions.
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