Power Plants for Telephone Offices 



By R. L. YOUNG 



Synopsis: The present paper gives a brief discussion of some of the 

 more important problems connected with the supplying of power to tele- 

 phone offices, and developments which are being perfected to bring about 

 economies. Among the subjects discussed are the use of commercial 

 types of charging generators together with appropriate filters, power factor 

 correction, complete power unit assemblies for small installations, and the 

 development of more nearly automatically controlled power installations 

 with the object of reducing supervision. 



I. The Power Problems 



The purpose of the telephone power plant is to furnish energy of the 

 required character in proper amount and available 100 per cent of the 

 time. An elaborate telephone system, comprising buildings, central 

 office equipment, outside plant lines and substation apparatus, together 

 with a staff of operators, is rendered useless if the supply of power fails. 

 No conversations can be held. No calls can be made and none re- 

 ceived. In a way, the power plant might be termed the "heart" of 

 the system, since every line and connection will be "dead " the moment 

 the supply of power is interrupted. 



Coiitinuity 



In order to meet the vital need of ever-ready power it is necessary in 

 telephone power plants to arrange for some primary power source 

 which is usually a commercial electric service from outside. The 

 services are investigated with care to determine their reliability and, 

 wherever possible, two services connected to different generating sta- 

 tions or systems are brought into the telephone building. In those 

 cases where a single service only can be secured, a local means of charg- 

 ing such as an engine-generator set may be provided as a reserve on 

 this service. 



Even with the best commercial power services short interruptions 

 are experienced, so that it is necessary to pro\'ide another source which 

 shall be available at all times to operate the central office during 

 temporary failures of the outside service. This is accomplished by 

 the use of a storage battery of sufficient capacity to carry the load of 

 the office during failure of the sources of power supply, the battery 

 being continuously connected to the circuits so no interruption occurs. 

 Common practice and experience have resulted in batteries of certain 

 sizes being provided, these sizes being sufficient to carry the exchange 



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