10. Cooling Type ONAN (Oil Natural Air Natural) •
Transformer oil circulates naturally (by convection) inside the tank, transferring heat from windings to tank walls; air cools the tank naturally. No fans or pumps required; it relies on natural convection and radiation. Standard cooling method Distribution transformers. Simple and reliable, but limited cooling capacity compared to forced methods.
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• Designation - “O” = Oil, “N” = Natural circulation, “A” = Air cooling, “N” = Natural air flow. KNAN (K-Class Oil Natural Air Natural) • Same cooling principle as ONAN, but uses K-class fluid (such as FR3 natural ester) instead of mineral oil. • Designation - “K” = K-class fluid, “N” = Natural circulation, “A” = Air cooling, “N” = Natural air flow.
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