high voltage DC for transmission may involve first conversion to AC so that the voltage may be stepped up to transmission levels using conventional transformers. The AC power would then be rectified to produce DC power. A more straight-forward approach would be to produce high voltage DC directly from the rectenna output. This possibility is discussed below under Design Option No. 2. Design Option No. 1 In both options, low voltage subelements are series-connected to provide 1000 VDC outputs. In this option, low voltage feeders (1000 V) are paralleled to supply power to 500 inverters averaging 10 MWe each. The rectenna is made up of 1000 rows of rectenna elements as shown in Figure IV-D-2-2. The average length of these rows is 9 KM; with rectenna output of 5 GWe, the average power per row is 5 MWe. The insulation between structural support and subelements will be sufficient to maintain 1000 V dielectric strength so that branch circuit ampacity is the primary design consideration. For the purpose of evaluating this option, a linear arrangement of variable size inverters has been assumed. The range of these is 1-50 MWe so that for conductor requirements, one inverter serves four half-rows with a mean length of 4.5 KM. Each of the four 1000 V branch circuits would supply an average of 2.5 MW or 2,500 amperes. Although conductors could be tapered from the rectenna edge towards the inverter, the size of structural elements is sufficient. At a temperature rise in free air of 45°C, 3-inch standard aluminum pipe will conduct this current. The high voltage AC produced by the inverters would then be transmitted through suitable switchgear and transformers to the grid. Design Option No. 2 This design option utilizes the same rectenna design as used in Option No. 1. However, the 1000 VDC terminals are connected in series to achieve a feeder output voltage of 250 KV DC. The subelements of this configuration are connected in parallel so that the ampacity of the 250 KV feeder is 2000 amperes. This provides for a feeder capacity of 500 megawatts. The structural support system may also be used as conductor material for completing the circuits in this design. In order to produce this voltage and power, the feeders are connected radially from the center of the rectenna. The feeder voltage of 250 KV requires protection from faults to the ground. To achieve this protection, each 1000 volt terminal must be insulated from ground by the amount of voltage it is above the ground. A typical value of 2.5 CM/kilovolt for
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