multi-conductor cables, and one must usually be satisfied with a lumped 

 circuit analytical approach using experimentally derived electrical 

 parameters. 



Single-Conductor Cable . Most E-M cables have at least two conduc- 

 tors. Single-conductor cables mostly include seafloor telegraph cables 

 and seafloor power cables. A detailed discussion of the electromagnetic 

 and lumped-circuit characteristics of ocean power cables is beyond the 

 scope of this report. However, it should be mentioned that an important 

 parameter in the single-conductor power cable is capacitance- to-ground, 

 which is the reason that AC-powered transmission over great distance is 

 not cost effective beyond a certain point, because of the per-cycle 

 energy required to charge capacitance. This is true of all single- 

 conductor and multi-conductor cable systems. For this reason, considerable 

 development effort is being devoted to AC-to-DC high-voltage conversion 

 techniques. AC is required to convert generator voltage to high voltage; 

 high voltage is required to minimize I^R losses over great distances; and 

 DC is required to minimize energy losses due to capacitive transmission 

 sys terns . 



The simplest design of a single-conductor ocean power cable is an 

 insulated copper rod pipe filled with oil maintained at pressures between 

 150 psi and 500 psi. Two separate pipe/conductor lines would be used for 

 a single-phase power system and three separate lines for a three-phase 

 system. Voltage is usually 69 kV or greater, and power ratings are on the 

 order of 100 MVA and above. The insulated conductor is usually shielded 

 (in the case of non-metallic pipes) with lead-alloy or aluminum sheaths 

 and sometimes metallized or carbon-black tape. 



Another type of single-conductor ocean power cable, which uses a 

 hollow conductor filled with oil, is stranded or contains openings which 

 allow the oil to penetrate through into the surrounding insulation. An 

 example of the hollow-conductor oil-filled power-cable system is the 

 seven-cable Long Island Sound submarine cable interconnection. *- u Rated 

 voltage and nominal power for this system are 138 kV and 300 MVA, respec- 

 tively. The single-conductor cables in this system could be regarded as 

 E-M types in that each cable has a layer of stranded steel armor, giving 

 the cable a weight of around 8 pounds/foot and a breaking strength of 

 approximately 50,000 pounds. The maximum depth for the cable is 200 feet 

 and the undersea distance is about 11 nautical miles. The cable can be 

 manufactured in splice-free lengths up to 35 nautical miles. For the 

 main crossing in deeper water, the cables are exposed to the sea and lie 

 directly on the bottom. 



Coaxial Cable . For wide-band long-distance signal transmission the 

 coaxial system is the most efficient. It is basically a circular-cross- 

 section wave guide with an axial conductor. The central conductor elimi- 

 nates the main disadvantage of the hollow-tube transmission line by allow- 

 ing the existence of a principal mode and, hence, propagation of signals 

 at all frequencies. In the hollow tube, only wavelengths on the order of 

 the tube diameter, or less, are allowed; hence, power frequencies and a 

 rather wide band of signal frequencies would be excluded in a hollowed 

 tube line of reasonable diameter. 



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