This standard specifies the characteristic quantities of precipitation and wind that affect electrical and electronic products and the classification of environmental conditions. This standard is applicable to determining the severity of precipitation and wind parameters that electrical and electronic products will be exposed to during transportation, storage and use. GB/T 4797.5-1992 Natural environmental conditions for electrical and electronic products: precipitation and wind GB/T4797.5-1992 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Natural environmental conditions for electric and electronic products
Precipitation and wind
Environmental conditions appearing in natureof electric and electronic productsPrecipitation and wind
GB/T 4797.5—92
This standard adopts the international standard IEC721-2-2 (1988) "Classification of environmental conditions Part 2: Environmental conditions appearing in nature Precipitation and wind".
Subject content and scope of application
This standard specifies the characteristic quantities of precipitation and wind affecting electric and electronic products and the classification of environmental conditions. This standard is applicable to determining the severity level of precipitation and wind parameters that electric and electronic products will be exposed to during transportation, storage and use. 2 Reference standards
GB4796 Classification of environmental parameters for electrical and electronic products and their severity classification GB4797.1 Temperature and humidity of natural environmental conditions for electrical and electronic products GB11804 Terminology of environmental conditions for electrical and electronic products 3 Precipitation
Precipitation includes rain, snow, ice, sleet and rime, etc. 3.1 Precipitation intensity
The maximum one-minute precipitation in each climate type in my country is listed in Table 1. Table 1 Maximum one-minute precipitation
Climate type
Cold temperature 1
Cold temperature 1
Sub-humid heat
Note: The climate type adopts the classification in GB4797.1. Approved by the State Administration of Technical Supervision on August 19, 1992, Maximum one-minute precipitation
Implemented on April 1, 1993
GB/T4797.5-92
The characteristics of rain are represented by rainfall intensity, raindrop size, falling speed and raindrop temperature. The raindrop temperature is generally the same as the wet bulb temperature of the ventilated psychrometer, but rain composed of ice crystals may deviate at the beginning of precipitation. The relationship between the other three is listed in Table 2.
Table 2 Characteristics of rain
Maximum rainfall intensity
Typical droplet diameter
0. 01~~ 0. 1
Raindrop falling speed
3.3.1 The diameter of snow is about 1mm or more. When strong winds blow, snow can break into small particles with a diameter as small as 20μm and an average of 80μm.
3.3.2 The density of new snow is 70-150kg/m2, and the density of old snow is 200-400kg/m2. 3.3.3 The maximum snow depth of each climate type in my country is listed in Table 3. Table 3 Maximum snow depth
Climate type
Saiwen 1
Subhumid heat
3.3.4 Blowing snow
Maximum snow depth
Blowing snow is the combined effect of snow and wind. When blowing snow, snow can be divided into very small particles, which are enough to pass through the tiny gaps and interfaces on the product. The horizontal flow rate of snow decreases rapidly with the increase of the distance from the ground. The maximum horizontal flow rate of snow is given in Table 4. 70
Height from the ground
GB/T4797.5-92
Maximum horizontal flow rate of snow
The characteristics of the snow are determined by the diameter, density, falling speed and collision energy of the snow block. The density of the ice block is about 900 kg/m, and the falling speed is calculated by formula (1): = 5. 16 VD
Where: z-
-falling speed, m/s;
block diameter, mm.
Maximum snow horizontal flow
g/(m2·s)
The collision energy can be calculated based on the mass (diameter and density) and falling speed. Table 5 lists the characteristics of the ice block. Table 5 Block characteristics
Falling speed
Collision energy
The ice block is a spherical or conical (also irregular) ice block with a diameter greater than 5 mm, and there may be tumor-like protrusions on the surface. The diameter of the largest ice block in the country exceeds 10 cm.
3.5 Rime
The density of rime is 0.2-0.3g/cm. In mountainous areas, rime can grow at a speed of 33mm/h, or 30cm overnight. When rime appears together with snow, it causes large areas of snow covering suitable objects. The maximum diameter of rime in various climate types in my country is listed in Table 6.71
Climate type
Cold and warm!
Subhumid and hot
GB/T4797.5—92
Table 6 Maximum diameter of rime
Maximum true diameter of rime
Note: In high mountainous areas above 1000m above sea level, due to the special climate, the maximum diameter of rime can reach more than 270mm. 3.6 Frost
Frost has a uniform and transparent ice layer. The thick frost often breaks the wires due to wind vibration. The maximum diameter of frost in various climate types in my country is listed in Table 7. Table 7 Maximum diameter of frost
Climate type
Cold and warm!
Subhumid and hot
Maximum diameter of frost
The wind in the atmosphere transports a large amount of moisture and heat, blows up sand and snow flakes, penetrates and damages equipment, and also causes air pollution and wind loads on overhead equipment.
4.1 Wind speed
The instantaneous maximum wind speed in various climate types is listed in Table 8. Table 8 Maximum wind speed (10m above the ground)
Climate type
Cold temperature 1
Maximum wind speed
Climate type
Cold temperature I
Subhumid heat
GB/T4797.5—92
Continued Table 8
Maximum wind speed
The terrain and altitude have a great influence on the wind speed. The rougher the surface, the smaller the wind speed near the ground. The wind speed decrease rate at an altitude of 500m is listed in Table 9.
Table 9 Relative wind speed at different heights in different regions Relative wind speed in different regions, expressed as a percentage of the wind speed at 500 m above ground Height above ground
4.2 Wind force
Town center high-rise buildings
Suburban forest area
Flat land, sea surface
The force exerted by wind on a component depends on the average wind speed, the shape and size of the object. The force on a plate perpendicular to the wind direction is calculated by formula (2).
F - 0. 65 vA
Where: F——force, N,
-average wind speed, m/s;
A——area of ​​the plate, m2.
· (2)
Gusts produce short-term force shocks, sometimes periodic, which can cause large amplitudes when they are in harmony with the natural response frequency of the object. The frequency of such gusts is usually less than 1 Hz.
The cylinder facing the wind releases a double row of vortices at the rear due to the action of the wind, which reacts on the cylinder perpendicular to the wind direction as a periodic force. The frequency of this force is given by formula (3): f= 0.195
Where:
Frequency, Hz;
Wind speed, m/s;
d-cylinder diameter, m.
A1 Rain, snow and flying
GB/T 4797.5-92
Appendix A
Occurrence of precipitation and wind
(reference)
The earth's atmosphere is in constant motion, so it will heat up, cool down and become humid locally. As a result, a gradient appears in density, resulting in high and low pressure areas. The existence of high and low pressure areas generates wind. Due to the Coriolis force of the earth's rotation, wind does not blow directly from high pressure areas to low pressure areas. The continuous horizontal movement of air causes a slow upward movement over a wide area. Or the surface heats up, causing the hot air to rise locally. The upward movement of the air causes the air pressure and temperature to drop. When both drop enough, precipitation will form. Various precipitation, rain, or snow are the result of complex processes in the cloud. The temperature of the cloud varies in the vertical direction. The layer where the temperature appears is called the freezing height. Above this, the temperature is below 0°C, and the temperature below this layer is above 0°C. In the clouds above the freezing height, supercooled water droplets often appear in the temperature range of 0 to 13°C, and can reach -50°C in special cases. The formation of raindrops or ice crystals depends on the vertical airflow, temperature distribution, and the synthesis process of droplets or ice crystals in the cloud. When the water droplets or ice crystals in the cloud are falling, the temperature changes from negative to positive through the cloud layer and remains positive. At this time, the water droplets or ice crystals become raindrops and fall to the ground. They continue to grow in size during the falling process, and the falling speed increases with the increase in the diameter of the raindrops. The relationship between the two is shown in Figure A1.
s/u"
Raindrop diameter, mm
Figure A1 at air pressure 101.At 3kPa and +20℃, the final velocity of raindrops in still air is 5-6mm in size and 9m/s in speed. Large raindrops will split into smaller raindrops, which will grow larger as they continue to fall. This is why the upper limit of the raindrop size distribution is 5-6mm. Raindrops will evaporate partially or completely during their fall. Usually, higher ground temperatures and higher relative humidity result in larger raindrops, so raindrops in tropical areas are larger than in temperate areas. The change in raindrop size due to evaporation at different relative humidities is shown by the curve in Figure A2.
GB/T 4797. 592
Raindrop diameter, mm
Relative humidity 50%www.bzxz.net
Relative humidity 90%
Figure A2 Change in raindrop size with height due to evaporation at different relative humidities Sometimes, raindrops may pass through a temperature transition layer in the atmosphere, where the temperature drops below zero again, and the raindrops freeze into blocks and fall to the ground. Alternatively, the raindrops remain as supercooled water droplets and freeze immediately when they hit the surface. In another case, the rising air currents carry the raindrops to a higher area with a temperature below zero, where they freeze. These blocks can be further enlarged by the formation of ice crystals on the surface, and when continuous freezing and melting processes occur, the blocks can reach very large sizes. If the temperature remains below zero throughout the fall, the ice crystals remain solid. They fall to the ground in the form of snowflakes. A42
Rime, rime and pure ice
Supercooled water drops or raindrops freeze on the surface to form rime, rime or pure ice. The three types of freezing depend on the air temperature, wind speed, diameter of the supercooled water droplets and the liquid water content. The relationship between the freezing type and the droplet diameter, wind speed and temperature is shown in the curves of Figures A3 and A4. n
Pure icing
Air overflow,
Figure A3 Three types of freezing as a function of air temperature and droplet diameter 75
"Thaw zone
GB/T4797.5---92
Pure icing
Air temperature, ℃
Figure A4 Three types of freezing as a function of air temperature and wind speed Rime is formed when supercooled water droplets are formed when the wind speed is low and the temperature is low. Rime appears when the raindrop temperature is slightly higher. Pure icing is formed under conditions between the two.
For a cylinder, there is an extreme when the wind speed and droplet diameter are different. Limit radius, beyond which there will be no or little freezing, Figure A5 shows the relationship between them.
Wind range, m/s
Figure A5 Cylinder limit radius (R,), beyond which there will be no or little freezing When the cylinder radius is small, supercooled water droplets will only freeze when the wind speed and droplet diameter are relatively small. On the contrary, when the cylinder radius is large, the droplet diameter and wind speed required for freezing can be increased accordingly. A3 Wind
The global wind system of the atmosphere is caused by high temperatures in the equatorial region and low temperatures in the polar regions, accompanied by the influence of the earth's rotation. Products are transported, stored and used. The wind conditions at a certain height above the ground should be considered for some applications. The wind in the lower atmosphere also depends on possible local heating caused by solar radiation and the shape of the surface, including buildings and other obstacles. Due to the influence of these local conditions such as friction and wind shear, thermal vortices and mechanical vortices are generated. The airflow near the surface during the day is the combined effect of these two conditions, and at night it is mainly mechanical vortices. GB/T4797.5—92
The influence of these vortices on the surface wind leads to an increase in gusts. The frequency of this gust is Random, usually with a time interval of several seconds. In atmospheric storms, wind speeds can reach very high. In tropical and subtropical storms, gusts of more than 80m/s have been measured on the ground. In land tornadoes, wind speeds may reach 125m/s, but the probability is very small. Additional notes:
This standard is proposed and coordinated by the National Standardization Committee for Environmental Conditions and Environmental Testing of Electrical and Electronic Products. This standard was drafted by the Guangzhou Electric Science Research Institute of the Ministry of Machinery and Electronics Industry, the Fifth Institute of the Ministry of Machinery and Electronics Industry, and the Seventh Institute of the China Shipbuilding Corporation.
The drafters of this standard are Xu Mengde, Li Zhiqing, and Huang Yuzhou.
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