Dry Type
Dry-type transformers are usually air cooled with winding insulation of class A, B, C, or H. The dry-type transformer can be either self-cooled or forced air cooled.
Self-cooled: A self-cooled transformer of the dry type is cooled by natural circulation of air through the transformer case. The cooling class designation for this transformer is AA.
Forced air cooled: A forced air-cooled transformer of dry type is cooled by means of forced circulation of air through the case. Transformers of this type have air-blast equipment such as fans with louvered or screened openings. These transformers are rated at 133% of the rating of the self-cooled dry-type transformers. The cooling class designation for this transformer is FA. Dry- type transformers can be obtained with both self-cooled and forced air-cooled rating. The designation for such a transformer is AA/FA. Dry-type trans- formers can also be cooled by gas instead of air. For such transformers, a sealed tank is required.