20 THE DESIGN OF STATIC TRANSFORMERS 



increase will not be simply in proportion to the increased 

 annual turnover of electrical machinery, but will constitute a 

 much larger percentage of the total annual turnover than is 

 now the case. Hence manufacturers who refrain from -taking 

 up the building of transformers are, in my opinion, ill-advised, 

 since they will not be so well prepared to participate in the 

 increasing turnover in electrical machinery. 



The Relative Merits of Various Types of Transformers. 



The two main types of transformers are the core type and the 

 shell type. The iron circuit of the former is composed of a 

 rectangular frame, upon the vertical legs of which the primary 

 and secondary windings are placed. In the shell type of trans- 

 former the windings interchange places with the iron magnetic 

 circuit of the core type, and the magnetic circuit is built around 

 the two vertical sides of the more or less rectangular-shaped 

 windings. It will thus be seen that, as regards mechanical 

 construction, the characteristics of the two types are precisely 

 reversed. In the core type the copper windings envelope a 

 considerable portion of the magnetic circuit, while in the shell 

 type the magnetic circuit envelopes a considerable portion of 

 the copper windings. Practically the entire surface of the 

 windings of the core type are exposed to the surrounding 

 medium (either air or oil), while in the shell type a very large 

 portion of the surface of the core is thus exposed. 



In Fig. 1 is shown an outline sketch of a representative 

 design for a core-type transformer. In this type it will be seen 

 that the two long parallel legs of the rectangular magnetic 

 circuit carry the primary and secondary windings, the latter 

 generally being next the core. A representative design for a 

 shell-type transformer is shown diagrammatically in Fig. 2. 

 Another type, illustrated in Fig. 3 and adapted from an illus- 

 tration in Kittler's " Handbuch der Electrotechnik " (1892), 

 may be designated the " circular-shell type." The arrange- 



