For those believing that voltage problems in space are minimal, the third option is attractive. The solar array and transmission line are operated at 400 kV, and power conditioners are provided to reduce the voltage for the transmitter tubes. Although this appears to be a high technology risk option, it cannot be rejected until more is known about high voltage effects and specific tube requirements. The final option considered was similar to terrestrial transmission systems where power conditioners are provided at each end of a high voltage de transmission line. This option allows independent selection of operating voltage for the transmitter tubes and the solar array as may be necessary depending on technology development. The mass required for power conditioning at each end of the transmission line makes this option the highest weight approach. 7.1.4.3 SWITCH GEAR In-line circuit protection is required for each 22 MW module in the system, as shown previously in Figure 7-15, to prevent power feedback from the main lateral buses. Crossed-field (Penning) discharge circuit breakers rated at 20 kV, 1.1 kA were tentatively selected. One feature of the distribution system is that lateral feed buses are not tied together (multiple circuit slip rings are required); therefore, excessively large circuit breakers are not required for isolation of the vertical feed buses. Solid state shorting switches are provided on the solar array to short circuit array sections during maintenance. 7.1. 4.4 POWER CONDITIONING The system voltage is regulated to within 1 percent to satisfy requirements of the amplitrons. The voltage of a solar array varies as a function of connected load, solar array orientation, solar cell temperature, and aging. The method selected for voltage regulation is to sequentially short out sections of the array. The location of the partial shunt regulators is indicated in Figure 7-15. The effects of solar array faults need to be analyzed also. 7.1. 4. 5 MAGNETIC FORCES A brief analysis was performed to estimate magnetic forces acting on power conductors. A model, consisting of a ring of four positive and four negative thin walled tubular conductors, was developed for the analysis. The total current was 105 A. Based on preliminary calculations, the forces appeared to be of a manageable level. The radial pressure tending to collapse each tubular conductor is 138 N/m2. Differential forces are 2. 2 N/m and 1. 8 N/m. The outward radial force on the eight conductors comprising the ring was 4.4 N/m.
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