TRANSATLANTIC CABLE POWER SYSTEM 



141 



ure of this two-motor alternator set has been essentially eliminated by 

 using two such sets, cross-connected to the rectifiers supplying power to 

 the two cables, with a continuously operating spare for each set, auto- 

 matically switched in upon failure of the regular set. 



The regulating features of the rectifiers will be described in a later 

 section. In the present discussion of reliability it is sufficient to note 

 that series regulating tubes are used, which are capable of acting as high- 

 speed switches, through which two rectifiers can be paralleled. Thus 

 either rectifier can accept instantaneously the entire load presented by 

 the cable. In each regulator the series tubes carrying the cable current 

 are furnished in duplicate and connected in parallel to share the cable 

 load, a single tube being capable of carrying the entire load. These cur- 

 rent regulators are operated from separate ac sources to protect against 

 loss of cable power because of failure of one of the sources of ac power. 



Cable Potentials 



To minimize the cable potentials, half of the dc power is supplied 

 at each end of each cable, the supplies being connected in series aiding. 

 With this arrangement, as shown in Fig. 1, the dc cable potential at one 

 end of each cable is positive with respect to ground while at the other 

 end the potential is negative. This places the maximum potential and 

 risk on the repeaters near the shore ends, which are more readily re- 

 trieved, while the repeaters in the middle of the cable, in deeper water, 

 have potentials very near to ground. The power equipment would be 

 simpler with a single-ended arrangement, but at the penalty of doubling 

 the dielectric stresses in the entire system, which would be prohibitive. 

 A balanced power feed could have been attained at the expense of 

 power separation filters in the middle of the cable or a shunt impedance 

 of appropriate size at the midpoint. The resulting complications, in- 



CLARENVILLE 



1950 VOLT 

 DC SUPPLY 



1950 VOLT 

 DC SUPPLY 



RECEIVING ^ 



I TRANSMISSION 

 DC POWER 



a 



SUBMARINE CABLE 



TRANSMITTING 



-3900 VOLTS 



TRANSMITTING 



s 



SUBMARINE CABLE 



RECEIVING 



-* — DC POWER 

 TRANSMISSION 



OBAN 



Fig. 1 — Cable voltage supplj', 



