Furuno WR110, Руководство по установке

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52
Assessment of annual number
𝑵
𝑿
of dangerous events:
According to the statistic information provided by the National Environment Agency of Singapore,
average thunderstorm days per year (
𝑇
𝐷
) at Changi is 168. The lightning ground flash density
𝑁
𝐺
will be leaded as follows:
𝑁
𝐺
≁ 𝐸. 1 𝑇
𝐷
= 16.8 [𝑓𝑙𝑎𝑠ℎ𝑒𝑠/𝑘𝑚
2
/𝑦𝑒𝑎𝑟]
I. Number of dangerous events
𝑁
𝐷
for the structure
𝑁
𝐷
may be evaluated as the product:
𝑁
𝐷
= 𝑁
𝐺
× 𝐴
𝐷
× 𝐶
𝐷
× 10
−6
where
𝑁
𝐺
is the lightning ground flash density
[𝑓𝑙𝑎𝑠ℎ𝑒𝑠/𝑘𝑚
2
/𝑦𝑒𝑎𝑟]
𝐴
𝐷
is the collection area of the structure
[𝑚
2
]
𝐶
𝐷
is the location factor of the structure, 0.5 for CWRP
1) Determination of the collection area
𝐴
𝐷
For isolated structures on flat ground, the collection area
𝐴
𝐷
is the area defined by the
intersection between the ground surface and a straight line with 1/3 slope which passes
from the upper parts of the structure (touching it there) and rotating around it. Determination
of the value of
𝐴
𝐷
will be performed graphically or mathematically.
For an isolated rectangular structure with length L, width W, and height H on flat ground, the
collection area is then equal to:
𝐴
𝐷
= 𝐿 × 𝑊 + 2 × (3 × 𝐻) × (𝐿 + 𝑊) + π × (3 × 𝐻)
2
where L, W and H are expressed in meters.
Figure A. 2: Collection area
𝑨
𝑫
of an isolated structure (IEC 62305-2)
2) Relative location of the structure
The relative location of the structure, compensating for surrounding structures or an
exposed location, will be taken into account by a location factor
𝐶
𝐷
. For the weather radar at
CWRP,
𝐶
𝐷
= 0.5
(Structure surrounded by objects of the same height or smaller).
II. Assessment of the average annual number of dangerous events
𝑁
𝑀
due to flashes near
a structure
𝑁
𝑀
may be evaluated as the product:
𝑁
𝑀
= 𝑁
𝐺
× 𝐴
𝑀
× 10
−6
where
[𝑓𝑙𝑎𝑠ℎ𝑒𝑠/𝑘𝑚
2
/𝑦𝑒𝑎𝑟]𝑁
𝐺
is the lightning ground flash density
[flashes/km
2
/year]
𝐴
𝑀
is the collection area of flashes striking near the structure
[𝑚
2
]
1:3
H
V
3H
L
IEC 2637/10