where S^ = stress in volts per mil at a point in the insulation r mils from 

 the cylindrical axis of the cable 



D^ = outside diameter of insulation in mils 



Dj = inside diameter of insulation in mils 



r = point in the cable insulation measured from the cylindrical 

 axis of the cable 



Using the above formula, the maximum stress will occur at the conductor 

 surface (r = D2/2), or 



^ 0.868 Volt 



^vmax 



d log 



(a 



The voltage levels considered for transmission of power from shore- 

 based plants were 5 kv, 15 kv, 34.5 kv, 69 kv, and 1 15 kv. At 69 kv and 

 1 15 kv, single-conductor cables are recommended. The three-conductor 

 cables rated for these voltage levels at the selected power levels and cable 

 lengths exceed current manufacturing capabilities. Further, the single- 

 conductor cables for 69 kv or 1 15 kv require a cable separation from 90 to 

 600 feet, depending on retrieval, maintenance, and repair requirements. 

 This would require multiple passes with a cable-laying vessel, resulting in 

 excessive deployment costs. For the larger cable lengths (500 miles), the 

 inductive and capacitive reactances would cause a changing current of many 

 times the load current. In addition, the size and weight of transformers at 

 69 kv and 1 15 kv required in the load module would be prohibitive when 

 related to the added size and cost of the load module. Therefore, the 69 kv 

 and 1 1 5 kv were eliminated from the study. 



A trade-off analysis was made of AC versus DC power transmission 

 systems for shore-based plants. The cost of engineering and deploying the 

 AC and DC systems was assumed to be equal for purposes of this analysis. 

 The three items considered to have a major influence in a cost effective 

 analysis of the two systems were cable costs, DC conversion and inversion 

 equipment, and the cost of the containment hull needed to house the DC 

 inversion equipment in the load module. 



A DC transmission system has distinct advantages over an AC system 

 when related to transmission cable requirements at the voltage and power 

 levels considered in this trade-off. The DC transmission cable has practically 

 no changing current, no ionic motion in the insulation, no induced current 



73 



