How are transformers classified?

Transformers are classified based on several criteria that reflect their design and application in the electrical system. The correct classification includes service, purpose, and method of mounting and cooling, which encompasses a wide range of transformers used in different contexts and for various functionalities.

Service refers to the operational role a transformer plays in a circuit—whether it's used for stepping up or stepping down voltage levels, thus impacting its design and manufacturing considerations. Purpose identifies what the transformer is intended for, such as power generation, distribution, or other specialized applications, informing its specifications and performance characteristics. The method of mounting and cooling relates to how transformers are physically installed in a given environment and how they dissipate heat—important factors in ensuring reliability and efficiency in operation.

This comprehensive classification allows for a structured approach to understanding transformers and their capabilities, making it essential for professionals in the field to grasp these distinctions to select the appropriate transformer for specific applications.

In contrast, the other choices may reference important characteristics of transformers but do not cover the classification as holistically as the correct answer. For instance, aspects like kilo-volt amperage rating or installation method are specific technical details rather than broad categories guiding classification.