280 



THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1957 



tant end only. Should the master end be switched off, the distant slave 

 unit will switch to master characteristic as soon as its output voltage 

 exceeds 2 kv. This abrupt disconnection of one equipment causes un- 

 necessary voltage surges on the cable, and when an equipment is re- 

 moved for normal maintenance purposes the following procedure is 

 adopted. The slave equipment is switched to the master characteristic 

 (an external key is provided for changing from master to slave or vice 

 versa, but see the limitation described in the next paragraph). This 

 leaves two master equipments feeding the cable, but any redistribution 

 of voltage is slow since the currents are approximately equal. An external 

 control (master/master shut-down), is then operated on the equipment 

 to be taken out of service, changing its characteristic to that shown in 

 Fig. 1(c). The output voltage of this unit will then be slowly reduced, 

 and when it is zero the equipment can be switched off without causing 

 surges on the cable. 



The current deviations occurring over the slave characteristic (c) 

 (from 4-2 per cent to —3 per cent) are the maximum permitted by the 

 tube design engineers for the tubes in the submerged repeaters, and 

 are permitted only for short periods. The circuit associated with the 

 manual switching of the equipment to the slave characteristic is there- 

 fore made inoperative if the output voltage exceeds 2 kv, since in this 

 range the slave characteristic is the extension of the line CAB on curve 

 (6) and the current is outside the permitted range. The slave characteris- 



CABLE 



TERMINATING 

 EQUIPMENT 



I 



REG 



POWER'" 

 EQUIPMENT 



ALT 



SYDNEY MINES 



14 

 REPEATERS 



GROUND 

 PLATE 



REPEATERS 



CABLE 

 TERMINATING 

 EQUIPMENT 

 I 



\ <? 



li 



I 



I SEA CABLE 



::::r\ 



It W 







REG 



GROUND 

 PLATE 



TERRENCE- 

 VILLE 



GROUND 

 PLATE 



LAND CABLE 



+> 



ALT 



_x_,. 



"■GROWER 

 EQUIPMENT 



CLARENVILLE 



Fig. 2 — Current paths on Clarenville-Sydney Mines link. 



