278 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1957 



For the Clarenville-Sydney Mines link a new and more reliable de- 

 sign of equipment has been developed. An automatic no-break system 

 provides an uninterrupted supply to repeaters unless equipments at 

 both ends of the link simultaneously fail to deliver power. 



The main improvement in the reliability of the equipment is the re- 

 placement of all high-power electron tubes by electromagnetic compo- 

 nents. The automatic no-break system takes advantage of the fact that 

 the rating of the repeater isolating capacitors has been chosen to permit 

 single-end feeding. Normally the link is fed from both ends, but in the 

 event of one equipment failing to deliver power the link is powered from 

 the other end without interruption to the cable suppl^^ If the failure is 

 due to a power-equipment fault, double-end feeding can rapidly be re- 

 established by manual switching to the standby. During an ac-supply 

 failure, single-end feeding must be maintained until the supply is re- 

 stored. In view of the very reliable no-break ac supply provided at both 

 stations, the possibility of a simultaneous ac supply failure at both ends 

 of the link is extremeh' remote. 



The power equipments at each end of the link must be capable of 

 suppl^dng the whole of the power to the cable should one end fail, which 

 requires that each should be capable of operating as a constant-current 

 generator. If two constant-current generators are connected in series, 

 unless precautions are taken, an unstable combination will result and 

 the unit suppl3'ing the higher current will driA-e the other unit 'off load.' 

 Manual adjustment could be provided to equalize the currents fed from 

 the two ends, but a different solution has been developed in which one 

 of the units is a constant-current master and controls the line current, 

 while the other unit is a slave whose voltage/current characteristic in 

 the normal operating range is such that its current is always equal to 

 that of the master unit. If the slave unit fails, the master will take over 

 the suppl}^; if the master unit fails, the slave unit will take over the 

 suppl}' and automatically assume the role of a master unit. The first 

 unit sAvitched on to an unenergized link operates as a master generator 

 and the other unit, on being switched on, automatically operates as a 

 slave. Other than ensuring that the link is safe for energizing, there is no 

 need for any cooperation between the two ends when putting the equip- 

 ment into service. 



DETAILS OF METHOD EMPLOYED 



The Master-Slave System of Operations 



The output-current/output-voltage characteristics for the equipments 

 are shown in Fig. 1, and are the same for both regular and alternate 



