The paper deals with special types of power transformers for electrical equipments. Climatic and altitude problems are examined in so far as they affect transformers. Transformer design and constructional features are presented with a view to obtaining the smallest possible transformer for a given rating. It is suggested that high-grade magnetic materials should be used for the cores, and that high-temperature insulating materials, such as the silicone products, be used to replace organic insulating materials. A design for a 500-VA 1 600-c/s transformer is given in the Appendix.