Value chain · CLM-1101
In plain terms
Lightning will hit a ten-kilometre receiver often, so Rice designed a grounded conductor into its structure at every bay, costing under one per cent of the collecting area; a single diode survives an ordinary strike, but the forty-thousand-volt strings they are wired into do not, and need the same surge protection as any transmission line.
The claim as recorded
Rice's 1980 lightning study for the reference rectenna recommends a distributed protection system, a horizontal conductor with points and grounds at every bay 14.69 m apart, built as a structural member of the rectenna, whose microwave shadow "is approximately 0.6% of the rectenna area" as "a maximum estimate of the loss"; it takes the 25 W GaAs diodes, which "have not been produced and no failure data is available for these devices", scales the HP5082-2824 by the "Wunsch relationship", assumes 67 V operation and about 100 V breakdown, and finds that "single diode configuration near rectenna center is safe" against the 98th-percentile flash at 10 m while the edge diode is vulnerable, that against the average flash "the individual diodes are self-protecting", but that in series strings of 597 diodes (40,000 V) the bottom diodes must carry the whole string's induced current and "The diodes cannot safely carry these currents", so "Standard surge protection practices are necessary for the string"; and it notes that power industries attribute 10 per cent of the cost of transmission equipment to lightning protection, which "should be added" if not already in the estimates.
Evidence behind this: T3-university study for MSFC: computer simulation, scale-model tests and sample computations; the diode failure data are scaled from another diode by a stated relationship.
Scope and limits
NO DIODE OF THE DESIGN EXISTED TO TEST; the failure power is scaled from a small-signal diode by the Wunsch relationship, and the flash fields are computed, not measured. The 0.6 per cent is for the conductor cross-section assumed (2 cm wide, 1 mm tube) and is a maximum. No cost is computed ("dollars" zero), and no flash density is given for a named site in the pages read; the study converts thunderstorm days by Pierce's formula.
What it assumes
The reference rectenna of 1980: 23 mW/cm2 (230 W/m2) at the centre, 1 mW/cm2 (10 W/m2) at the edge, 25 W diodes, 597 x 67 V = 40,000 V strings; flash parameters from the study's Table 8.4.
Where it comes from
PDF 5 / printed iv, normalised: "The very high lightning flash density in many parts of the United States and the large size of the SPS rectenna require us to incorporate lightning protection systems in the rectenna design"; "should be incorporated as a structural member of the rectenna support system"; "these shadow areas are only a slight fraction of the collecting area"; "and those near the center of the rectenna are safe from extreme lightning"; "the series connection of the diodes to form 40,000 V strings creates a protection requirement for the string"; raw: "Standard surge protection practices are necessary for the string"; normalised: 10 per cent "of the cost of power transmission equipment to lightning protection requirements" (the layer prints "103" for "10%") and "If this factor is not already included in cost estimates, it should be added". PDF 6 / printed v, raw: "14.69 meters apart". PDF 46 / printed 37, normalised: "The assumed shadow of these structures is approximately 0.6% of the rectenna area" and "This is a maximum estimate of the loss"; PDF 47, Figure 30: bay 12.24 m x 14.69 m = 179.81 m2, shadow (0.04 m)(12.24 m + 14.69 m) = 1.08 m2 (layer, "l, 08M2"). PDF 48 / printed 39, normalised: the 25 W GaAs diodes "have not been produced and no failure data is available for these devices"; raw: "Wunsch relationship", "HP5082-2824". PDF 68 / printed 59, render read: "We assume that a diode designed to operate at 67 V will have a breakdown voltage of about 100 Volts"; the sample computation (250 W failure power x 3 x 10^-6 s = 7.5 x 10^-4 J; 7.5 x 10^-6 C across 100 V; 19.38 x 10^-6 C/m2 induced; 0.39 m2); area served per diode 25 W / 230 W/m2 = 0.11 m2 at the centre and 25 W / 10 W/m2 = 2.5 m2 at the edge; normalised: "single diode configuration near rectenna center is safe"; raw: "the diodes are to be put in series (597 to a string)"; normalised: "would require fast surge protection diodes (back to back zeners) on all diodes in the rectenna" and "This extent of protection may not be cost effective". PDF 69 / printed 60, normalised: "the individual diodes are self-protecting and able to take an" average flash; raw: "The diodes cannot safely carry these currents". PDF 72 / printed 63, normalised: "We have found it necessary to use the number-of-thunderstorm days as a proxy variable" with the Pierce formula.
Basis: per cent of collecting area shadowed; volts; watts; m2 of rectenna served per diode; diodes per string
Related records
- Answers question
- QST-007 not published in this release
Cite this
energyaperture.com/c/clm-1101
CLM-1101, Energy Aperture, as of 1980-11.