Furuno WR2120 Installation Manual page 53

2.2.2. Assessment of annual number
According to the statistic information provided by the National Environment Agency of Singapore,
average thunderstorm days per year (
will be leaded as follows:
2.2.2.1. Number of dangerous events
may be evaluated as the product:
where
is the lightning ground flash density
is the collection area of the structure
is the location factor of the structure, 0.5 for CWRP
1) Determination of the collection area
For isolated structures on flat ground, the collection area
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
For an isolated rectangular structure with length L, width W, and height H on flat ground, the
collection area is then equal to:
where L, W and H are expressed in meters.
Figure A-2: Collection area
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
(Structure surrounded by objects of the same height or smaller).
2.2.2.2. Assessment of the average annual number of dangerous events
structure
may be evaluated as the product:
where
is the collection area of flashes striking near the structure
of dangerous events
for the structure
will be performed graphically or mathematically.
H
is the lightning ground flash density
) at Changi is 168. The lightning ground flash density
1:3
3H
V
L
IEC 2637/10
of an isolated structure (IEC 62305-2)
11
S2E-17-0209_IM_WR2120_C
is the area defined by the
. For the weather radar at CWRP,
due to flashes near a