What does the second letter 'N' denote in the cooling class of transformers?

The second letter 'N' in the cooling class designation of transformers signifies "Natural convection through cooling equipment and windings." In transformer cooling classifications, letters are used to indicate the method of heat dissipation. The designation 'N' specifically refers to cooling that relies on the natural movement of heated fluid—such as air or oil—around the transformer.

In practical terms, this means that the heat generated by the transformer is dissipated into the environment without the use of fans or pumps to enhance circulation. Instead, the process relies on natural convection, where warmer fluid rises and cooler fluid moves in to replace it, allowing for effective cooling through passive means. This is commonly found in smaller transformers, where major cooling systems are not necessary, making operation simpler and often more economical.

This understanding is crucial in transformer design and operation, as it has significant implications for the efficiency and thermal management of the equipment.