TRANSATLANTIC CABLE POWER SYSTEM 143 



eluding difficulty in the location of a cable fault, could not be justified 

 for the sake of simplification of power-plant design and operation. 

 * The requirement that minimum cable potentials be maintained during 

 and after severe earth potential disturbances necessitates variable out- 

 put voltages from the supplies at both ends, and this introduces problems 

 in continuous voltage balance and regulation stability. The design 

 features which yield the required performance are described in a later 

 section. 



DC Cable Current Regulation 



The salient requirements in performance of the constant current 

 regulator are listed below : 



a. The regulator must have extremely fast response to hold the cable 

 current within a few milliamperes of its nominal value should a short 

 circuit develop in the cable. Thus damage to the heaters of the re- 

 peater tubes, as well as excessive induced transient voltages in the re- 

 peater transformers is avoided. The probability of a short circuit is higher 

 near the shore ends where the water is shallow and sea traffic a factor. 

 The regulator must be capable of absorbing the reduction in power to 

 the cable, while maintaining current control under normal conditions. 

 This sudden exchange in power from cable to regulator may be as much 

 as 2,000 volts at 0.25 ampere. 



b. The cable current should be maintained constant within 0.2 per 

 cent of its nominal value for normal variations in ac supply, gradual 

 earth potential changes, and ambient temperature changes. This degree 

 of regulation allows an adequate safety factor in maintaining a 

 constant transmission level. ^ 



c. The regulators, in conjunction with the power separation filters 

 and the rectifier filters, must limit the power supply noise at the cable 

 terminals to a peak-to-peak valueless than 0.02 percent of the dc supply 

 potential. 



d. The cable current must be adjustable over a range of 225 to 245 

 milliamperes to compensate for repeater tube aging. ^ 



e. The regulators must operate in parallel in such a way as to ensure 

 continuity of power should one fail or be removed from service for main- 

 tenance. This of course implies that regulators can be switched in and 

 out of service without causing surges in the cable current or voltage. 



f. The series-aiding arrangement, with rectifiers at each end of the 

 same cable, must be stable. 



g. The regulators should be capable of being serviced at low poten- 



