412 



ALTERNATING CURRENTS 



within a sub-station may require a large building and hence a 

 considerable investment. The investment in equipment and 

 in buildings situated along transmission lines and supply ing small 

 loads may be large compared with the kilowatt-hours consumed. 

 Sub-stations for small loads would not be economically possible 

 were it necessary to place all the apparatus within a building. 

 Transformers, switches, lightning arresters, have been designed 



FIG. 375. Outdoor sub-station, showing transformers, oil switches, bus-bars, 

 etc. (Dallas Power and Light Co.) 



so that it is possible to operate them out of doors. The building 

 needs only to house the switchboard and the operator, if one is 

 necessary. The oil switches, the lightning arresters, the trans- 

 formers, and the bus-bars can all be placed out of doors. The 

 apparatus must be practically air tight to keep out moisture. 

 Outdoor sub-stations on a large scale are highly developed at the 

 present time. Figure 375 shows an outdoor sub-station of 

 moderate size. 



