Voltage regulation of selected power transmission systems for shore- 

 based plants is of major importance because of the long cable lengths. Voltage 

 regulation for AC systems is affected the most by changing currents. Normally, 

 the AC voltages at each end of the system are kept within desired limits by 

 automatic tap changers on the transformers provided. 



DC high voltage is normally regulated by controlling the rectifier firing 

 angle to produce the required DC current and by operating the inverter with 

 the maximum firing angle necessary for safe commutation. 



The protection system for shore-based generator plants will be similar 

 to that of the surface plant system. Where DC transmission is required, the 

 protection system must also protect the DC equipment, which includes con- 

 verter, DC transmission cable, and inverter. The AC transformers at either 

 end of the DC system are protected with a differential relay circuit similar to 

 the surface plant arrangement. The inverter equipment would have failure 

 detectors, voltage sensors, and monitoring and control devices to cover such 

 conditions as commutation failure, pulse synchronization, and fire-through. 

 The converter or rectifier would also be similarly protected. All DC faults 

 are referred to the AC systems at both ends of the DC link. The protection 

 system should provide a means to differentiate between DC cable faults, 

 inverter faults, and load module faults. 



DEPLOYMENT CONCEPTS 



The deployment of the three underwater power transmission systems, 

 in-situ, surface- tendered, and shore-based, involves unique problems in the 

 emplacement of cable in the deep ocean. Some of the major problems include 

 induced cable oscillations due to ship or hull motion, high cable loading on 

 storage drums, twist induced in long cables, and the placement and recovery 

 of the large modules and associated components. 



A route and site survey is of utmost importance in obtaining data for 

 the design and deployment of an underwater power system. A bottom survey 

 should be conducted to determine topography, sediment characteristics, 

 temperature, and current profiles. Sediment information would also be 

 required to determine the correct anchoring configuration. Temperature 

 and current profiles are necessary to define the temperature effects on 

 structures and materials as well as the current forces which cables and 

 structures may be subjected to. 



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