1、BSI Standards PublicationClassification of environmental conditions Part 2-2: Environmental conditions appearing in nature Precipitation and windBS EN 60721-2-2:2013National forewordThis British Standard is the UK implementation of EN 60721-2-2:2013. It is identical to IEC 60721-2-2:2012. It superse
2、des BS 7527-2.2:1991, which will be withdrawn on 17 January 2016.The UK participation in its preparation was entrusted to TechnicalCommittee GEL/104, Environmental conditions, classification and testing.A list of organizations represented on this committee can be obtained onrequest to its secretary.
3、This publication does not purport to include all the necessary provisions ofa contract. Users are responsible for its correct application. The British Standards Institution 2013.Published by BSI Standards Limited 2013ISBN 978 0 580 73595 0ICS 19.040Compliance with a British Standard cannot confer im
4、munity fromlegal obligations.This British Standard was published under the authority of theStandards Policy and Strategy Committee on 31 August 2013.Amendments/corrigenda issued since publicationDate Text affectedBRITISH STANDARDBS EN 60721-2-2:2013EUROPEAN STANDARD EN 60721-2-2 NORME EUROPENNE EURO
5、PISCHE NORM August 2013CENELEC European Committee for Electrotechnical StandardizationComit Europen de Normalisation ElectrotechniqueEuropisches Komitee fr Elektrotechnische Normung Management Centre: Avenue Marnix 17, B - 1000 Brussels 2013 CENELEC - All rights of exploitation in any form and by an
6、y means reserved worldwide for CENELEC members. Ref. No. EN 60721-2-2:2013 E ICS 19.040 Supersedes HD 478.2.2 S1:1990 English version Classification of environmental conditions - Part 2-2: Environmental conditions appearing in nature - Precipitation and wind (IEC 60721-2-2:2012) Classification des c
7、onditionsdenvironnement - Partie 2-2: Conditions denvironnement prsentes dans la nature - Prcipitations et vent(CEI 60721-2-2:2012) Klassifizierung vonUmgebungsbedingungen - Teil 2-2: Natrliche Umgebungsbedingungen - Niederschlag und Wind(IEC 60721-2-2:2012) This European Standard was approved by CE
8、NELEC on 2013-01-17. CENELEC members are bound to complywith the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standardthe status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standar
9、ds may be obtained onapplication to the CEN-CENELEC Management Centre or to any CENELEC member. This European Standard exists in three official versions (English, French, German). A version in any otherlanguage made by translation under the responsibility of a CENELEC member into its own language an
10、d notifiedto the CEN-CENELEC Management Centre has the same status as the official versions. CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus,the Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germa
11、ny,Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland,Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom. BS EN 60721-2-2:2013EN 60721-2-2:2013 - 2 - Foreword The text of document 104/583/FDIS,
12、 future edition 2 of IEC 60721-2-2, prepared by IEC TC 104“Environmental conditions, classification and methods of test“ was submitted to the IEC-CENELECparallel vote and approved by CENELEC as EN 60721-2-2:2013. The following dates are fixed: latest date by which the document has to be implemented
13、at national level bypublication of an identical national standard or by endorsement (dop) 2014-02-02 latest date by which the national standards conflicting with the document have to be withdrawn (dow) 2016-01-17 This document supersedes HD 478.2.2 S1:1990. EN 60721-2-2:2013 includes the following s
14、ignificant technical changes with respect toHD 478.2.2 S1:1990: subclause Precipitation: simplified; data not possible to validate are removed; subclause Wind: text rewritten; Table 1 simplified and aligned with definition used by 1; subclause Hail: data added; formula changed; formula for impact en
15、ergy added; subclause Snow: text changed and aligned with definitions used by 1; Table 3 removed; subclause Normal rain: text has been modified and numeric values removed; subclause Driving rain: text has been modified and numeric values removed; subclause Formation of ice: text has been modified an
16、d numeric values removed; subclause Drifting snow: text added; subclause Wind force: formula changed; Figures 1 to 5 removed. Attention is drawn to the possibility that some of the elements of this document may be the subject ofpatent rights. CENELEC and/or CEN shall not be held responsible for iden
17、tifying any or all such patentrights. Endorsement notice The text of the International Standard IEC 60721-2-2:2012 was approved by CENELEC as a EuropeanStandard without any modification. BS EN 60721-2-2:2013- 3 - EN 60721-2-2:2013 Annex ZA (normative) Normative references to international publicatio
18、nswith their corresponding European publications The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undatedreferences, the latest edition of the referenced docu
19、ment (including any amendments) applies. NOTE When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HDapplies. Year Publication EN/HD Title Year IEC 60721-1 - Classification of environmental conditions - Part 1: Environmental parameters and
20、theirseverities EN 60721-1 - BS EN 60721-2-2:2013 2 60721-2-2 IEC:2012 CONTENTS 1 Scope . . 5 2 Normative references . 5 3 Terms and definitions . 5 4 General . 5 4.1 Introductory remark . 5 4.2 Precipitation . 5 4.3 Wind . . 6 5 Characteristics . . 6 5.1 Rain . . 6 5.2 Hail . 7 5.3 Snow . 8 5.4 Win
21、d . . 8 6 Classification 8 6.1 General . 8 6.2 Normal rain 8 6.3 Driving rain . 9 6.4 Formation of ice . . 9 6.4.1 General . 9 6.4.2 Air hoar . 9 6.4.3 Rime . 9 6.4.4 Clear ice . . 9 6.4.5 Glaze ice . 9 6.4.6 Process of ice formation . 9 6.5 Hail . 10 6.6 Snow load 10 6.7 Drifting snow . 10 6.8 Wind
22、 force 10 Bibliography . 12 Table 1 Characteristics of rain (average over long periods) . 6 Table 2 Characteristics of hailstones . 8 BS EN 60721-2-2:201360721-2-2 IEC:2012 5 CLASSIFICATION OF ENVIRONMENTAL CONDITIONS Part 2-2: Environmental conditions appearing in nature Precipitation and wind 1 Sc
23、ope This part of IEC 60721 presents fundamental properties, quantities for characterization, and a classification of environmental conditions dependent on precipitation and wind relevant for electrotechnical products. It is intended to be used as background material when selecting appropriate severi
24、ties of parameters related to precipitation and wind for product applications. When selecting severities of parameters related to precipitation and wind for product application, the values given in IEC 60721-1 should be applied. 2 Normative references The following documents, in whole or in part, ar
25、e normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60721-1, Classification of environmental conditions
26、 Part 1: Environmental parameters and their severities. 3 Terms and definitions Terms and definitions are defined, in context, throughout the present standard. 4 General 4.1 Introductory remark The atmosphere of the Earth is in permanent motion. It is locally heated, cooled and moistened. The result
27、ing gradients in density create high and low pressure areas. The equalizing winds do not blow directly from high to low pressure areas, but are deflected by Coriolis force due to the rotation of the Earth. The continuous horizontal movement may cause slow upward motion over wide areas, or surface he
28、ating may give more localized updrafts in thermals. The air cannot maintain its water content in vaporous form if the reduction of pressure and temperature is sufficient, and precipitation may form. As an example, an air mass at +20 C temperature is able to contain water in a quantity of 17,3 g/m3in
29、 vaporous form. If it cools to 0 C the maximum water content is only 4,8 g/m3. 4.2 Precipitation The specific kind of precipitation (rain, hail or snow) is a result of complicated processes in the clouds. BS EN 60721-2-2:2013 6 60721-2-2 IEC:2012 Formation of raindrops or ice crystals depends on var
30、ious conditions, for instance vertical air currents, temperature distribution, and the resulting course of droplets or ice crystals within the cloud. 4.3 Wind Wind is defined as lateral movement of the Earths atmosphere from high-pressure areas to low-pressure areas. Winds are often referred to by t
31、heir strength and the direction from which the wind is blowing. Gusts are short bursts of high speed wind. Winds of long duration have various names associated with their average strength, such as breeze, gale, storm, hurricane and typhoon. Wind occurs on a scale ranging from thunderstorm flows, las
32、ting tens of minutes, through local breezes generated by heating of land surfaces and lasting a few hours, to global winds resulting from the difference in absorption of solar energy between the climate zones on Earth. The two main causes of large scale atmospheric circulation are the differential h
33、eating between the equator and the poles and the rotation of the planet. 5 Characteristics 5.1 Rain Rain is characterized by the following physical parameters: rain intensity measured in millimetres per hour (as the height accumulated on a horizontal surface without drain); drop size distribution; t
34、ypical 1 mm to 2 mm in diameter, in thunderstorms the size could be up to 5 mm to 8 mm; falling velocity distribution; typical 2 m/s to 12 m/s; raindrop temperature. Other parameters such as dissolved impurities due to air pollution, sea salts, etc., are not considered here, even though they may hav
35、e important effects on products. A survey of characteristic parameters for different types of rain is given in Table 1 below, in accordance with 1. Table 1 Characteristics of rain (average over long periods) Type of rain Rain intensity upper limit mm/h Very light rain Light rain Moderate rain Heavy
36、rain Very heavy rain Extreme rain 0,25 1,0 4,0 16 50 50 The raindrop temperature will normally be the same as the wet bulb temperate of an aspirated psychrometer but deviations may occur, for instance in a rain established from ice crystals or at the beginning of a period of rainfall. BS EN 60721-2-
37、2:201360721-2-2 IEC:2012 7 5.2 Hail Hail is characterized by the following physical parameters of the hailstones: null diameter; typical 5 mm to 15 mm; null density; typical large hail greater than 800 kg/m3and small hail less than 800 kg/m3; null falling velocity; null impact energy; null typical d
38、rag coefficient (Cd) is 0,6 but depends on hail size, irregularities in shape and in surface roughness 2. Only stones of larger diameter are considered here because of their damaging effect but stones of smaller diameter are by far the most frequent 1. The falling velocity is determined by the formu
39、la: ACWv =0 d2where is the falling velocity in metres per second; W is the weight (massacceleration); Cdis the drag coefficient; 0is the atmospheric density in kg per cubic metres; A is the frontal area in square metres. 0 = 1,225 kg/m3(standard atmosphere for dry air at sea level and at +15 C). The
40、 impact energy is then calculated from the mass (diameter, density) and the falling velocity. The impact energy is determined by the formula: 2m2vE =where E is the impact energy in Joules; m is the mass of the hail in kg; is the falling velocity in metres per second. Table 2 gives the characteristic
41、s of hailstones with diameters from 20 mm upwards. BS EN 60721-2-2:2013 8 60721-2-2 IEC:2012 Table 2 Characteristics of hailstones Diameter mm Mass g Falling velocity m/s Impact energy J 20 4 18 1 50 59 28 24 60 102 31 49 70 162 34 91 80 241 36 155 90 344 38 248 100 471 40 378 NOTE Values are in rou
42、nd figures. The following values are used in Table 2: Cd= 0,6; = 900 kg/m3 (for hailstones). 5.3 Snow Snow is generated as snow crystals are formed by freezing water droplets. If blown by strong winds, however, snow crystals are broken and abraded into small particles. Freshly fallen snow has a dens
43、ity ranging from 70 kg/m3to 150 kg/m3whereas the density of old snow could be in a range of 400 kg/m3to 500 kg/m3, even up to 910 kg/m3. If the density exceeds 910 kg/m3, snow is considered as ice. Firm snow will normally have a density of 600 kg/m3. Wind exposure will often increase the density by
44、breaking the snow flakes; temperature will also increase the density. Density will also increase over time due to settling 1. 5.4 Wind Wind speed is greatly influenced by details of the local landscape and height above the ground. The greater the roughness of the ground surface, the more the wind sp
45、eed close to this surface is reduced; thus there may be considerable differences between wind speeds near the ground surface and those at greater heights above the ground surface. 6 Classification 6.1 General Rain, hail, snow and wind may have various effects on products, either separately, mutually
46、 combined or in combination with other environmental parameters. Some examples of single and combined parameters are given below. 6.2 Normal rain Rain occurs with very different intensities which vary considerably with latitude, climate and season. Generally, the highest rates occur in tropical thun
47、derstorms and in hurricane-type storms. Normal rain consists of drops of different sizes and velocities. The characteristics of the drops depend mainly on the temperature and the moisture content in the atmosphere. These atmospheric features result in partial or complete vaporization of the falling
48、drops. In general, higher ground temperatures and higher relative humidity give greater median drop size. BS EN 60721-2-2:201360721-2-2 IEC:2012 9 Consequently, tropical rain generally consists of drops larger than those of rain in, for example, a north European location. 6.3 Driving rain Driving ra
49、in is a combination of rain and wind. The wind adds a horizontal velocity component to the falling velocity, and may further create underpressure in an encapsulation. The rain itself may also create such underpressure by cooling due to low rain temperature. 6.4 Formation of ice 6.4.1 General Formation of ice occurs as a combination of rain falling on a surface cooled below 0 C (for example, due to radiation towards a clear night sky), or by super-cooled
