POWER PLANTS FOR TELEPHONE OFFICES 



703 



load for intervals ranging from a few hours to several days, depending 

 upon conditions. The present practices have been successful in main- 

 taining continuous power supply, and central offtces generally through- 

 out the country haAe been ready to serve, even during periods of storm, 

 fire or other calamities. 



Type of Poiver Needed 

 Power as furnished by the public service companies is not of the sort 

 suitable for operating telephone power plants, but must be converted 

 from a relatively high voltage alternating or direct current to a lower 



p'ig. 1 — Incoming direct-current power for large telephone building. About 

 1,000 h.p. of this is provided to drive motor-generators for reserve central office use, 

 the regular power being alternating current. Both direct- and alternating-current 

 services are duplicated. This panel provides four feeders direct to substation and 

 four to network, capacity 3,480 kw. 



voltage direct current for talking, supervisory and signaling purposes 

 and to alternating current of various voltages for signaling. This 

 conversion is commonly made by means of motor-generator sets or some 

 type of rectifier, of either the mercury arc, hot cathode or other types. 

 Since it is impossible to use outside power as furnished, suitable reserve 

 machine equipment must be provided capable of replacing the regular 

 machines before the reserve energy in the central office battery is ex- 

 hausted. 



