TRANSMISSION OF POW1-: I! KY ALTERNATING CURRENT \ 1 1 



oil switches, etc., on some form of balcony or else inside an 

 enclosure so that the possibility of personal contact is minimized. 

 177. Automatic Sub-stations. In order to eliminate the cost 

 of having an attendant in the smaller sub-stations, automatic 

 sub-stations have been developed. These are particularly 

 adapted to electric railway work. After the trolley voltage in the 

 vicinity of the station has fallen below a predetermined value 

 and remained there for a minute or so, a combination of relays 

 and switches starts up one of the synchronous converters or 



7\. Automatic railway sul>--tation. Pacific Hailway, showing KlOO-kw. 

 hrormus converter and automatic control equipment. 



motor-L'enerator sets and connects it to the trolley line. If the 

 load on tli.- >tation exoeedfl the safe load of the machine in 

 06 at that time, another machine starts up automatically 

 and after it i- .-..rmected across the line, the field rheostat up. 

 to make it take it- share of the load. Likewise, the machines 

 drop out of service automat ically after I he ]uad has fallen below a 

 predetermined value. I'IL:. :!74 shows the interior of one <f these 

 stati< 



178. Outdoor Sub-stations. When the voltage is high, the 

 required by the high-tension leads and bus-bare 



