IEEE 3-1962 - AIEE Guiding Principles for the Selection of Reference Values for Electrical Standards.pdf

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1、IEEE STANDARDSARCHIVESDO NOTR!EMOVGUIDING PRINCIPLES FOR THEAlEENo.3Dec. 1962SELECTION OF REFERENCE VALUESFOR ELECTRICAL STANDARDSPublished byAMERICAN INSTITUTE OF ELEcrRlCAL ENGINEERS345 East 47 Street, New York 17, N. Y.CONTENTS Purpose 3 TemperaturesBarometric Pressure 4 AltitudeRelative Air Dens

2、ityHumidity 5 Absolute Humidity 6 Relative HumidityBibliography 7 ACKNOWLEDGMENT The Institute wishes to acknowledge its indebtedness to those who have so freely given of their time and knowledge and have conducted experimental work on which many of the AIEE publications are based. The major work of

3、 preparing this publication was carried out by the Standards Coordi nating Committee No. 1 of AIEE Standards Committee. Personnel of Standards Coordinating Committee No. 1 P. H. McAuley, Chairman F. M. Defandorf J. H. Hagenguth H. P. Walker 2 GUIDING PRINCIPLES FOR THE SELECTION of REFERENCE VALUES

4、FOR ELECTRICAL STANDARDS 3-1 PurposeTest results and general perform ance of electric apparatus, conductors and ma terials frequently are influenced by conditions such as Temperature, Pressure, Altitude, Den sity and Humidity of the surrounding air or other medium. For comparative results, it is nec

5、essary to standardize the conditions under which tests are made or to which test results are corrected. Other conditions which may affect tests or operating performance for par ticular apparatus are Contamination, Surges, Vibration, Shock or Radiation. Since these are not of general application, sta

6、ndardization should be left to the apparatus groups con cerned. This pamphlet serves as a guide in the prepa ration or revision of standards for testing or performance* of apparatus or materials of spe cific types or fields of use. If a particular exist ing standard calls for other provisions, the e

7、xisting standard should be followed. The values given are not mandatory, but are recommended for use in preference to other values unless there are good technical or economic reasons for using others. The values recommended have in general been selected to agree with well-established practices parti

8、cularly in the power and industry fields. Provisions are made for a great variety of conditions and for widely different apparatus and materials, some of which may be of prac tical importance only under unusual circum stances. In an individual standard, only those quantities of real practical import

9、ance in the particular case should be used. When ranges are suggested, it is generally with the thought that acceptance tests may be made within that range. Tests may be made outside the range, if acceptable, and agreed-upon correction factors are available. For various good reasons different refere

10、nce values have become firmly established some times in the same field for the same type of tests. Dielectric tests on insulation are an ex ample. Flashover tests in International usage are referred to 20C and 11 grams per cubic meter absolute humidity (65 percent relative humidity). In the U.S.A. t

11、he references for flashover tests are 25 C and 0.6085 inch of mer cury vapor pressure (65 percent relative humid ity). For a standard laboratory atmosphere and for conditioning and weathering insulating ma terials, 23C and 50 percent relative humidity have been selected. Although a single set of ref

12、erences might be considered desirable, the effects on such considerations as laboratory practices, catalog data and insulation levels would seem to preclude changes. 3-11 Range of Ambient Temperatures for Tests are values defining a range of temperatures considered suitable for acceptance and check

13、tests. * For standard temperatures for rating purposes, see AIEE Standard No. 1. h* Current usage in electrical standards prescribes the use of the Centigrade temperature scale. TEMPERATURES * Definitions 3-10 Standard Reference Temperature is a suitably selected temperature value for which test rec

14、 ords or performance data are given in records and standards of various kinds and to which the results of tests made at different tempera tures are corrected for purposes of comparison and standardization. Preferred Values 3-15 Standard Reference TemperaturesPrefer ence should be given to 20 C (68 F

15、), 23 C (73.4 F) and 25 C (77 F). (Although a single value would be desirable, these values have become firmly rooted in their respective fields and universal adoption of one or the other may not be practicable. More defi nite recommendation of one value may be made in future issues of this report i

16、f a substantial unanimity of opinion can be developed. In order to avoid further diversification of values, one of these values should be used unless there are compelling reasons for not doing so. Where International Standards give one of these values and United States Standards another, it is rec o

17、mmended that both sets of values be tabulated in some cases, for example, sparkover values for sphere gaps. In specific fields, the following values have been used, although the list is by no means complete: Dielectric tests on apparatus: 20C (68 F) International Dielectric tests on apparatus: 25C (

18、77 F) U.S.A. Dielectric tests on materials: 23C (73.4 F) U.S.A. Ohmic resistance (except in machines and apparatus) 20 C (68 F) 3 Ohmic resistance (in machines and apparatus) 25C (77 F) Physical and electrical constants 25C (77 F) 20C (68 F) 15C (59 F) OC (32 F) Mechanical 20C (68 F) Mil Specs -55C

19、(-67 F) 71C (160 F) 100C (212 F) ASTM Standard Laboratory Atmosphere 23 2C (73.4 3.6 F) ISA Measurements Standard Laboratory 23C (73.4 F) Range of Ambient Temperatures for Tests 3-20 Following are the preferred ranges for use: 1st preference 10 C to 40 C (50 F to 104 F)* 25 C to 40 C (13 F to 104 F)

20、* 30 C to 55 C (22 F to 131 F) 2nd preference 20 C to 30 C (68 F to 86 F)* 0 C to 40 C (32 F to 104 F)* 55 C to 85 C (67 F to 185 F) Jiduicfumm UseFrefenedTciupeialuTes hi -line Wllli Appendix I. BAROMETRIC PRESSURE, ALTITUDE, AND RELATIVE AIR DENSITY Barometric Pressure Definitions 3-50 Standard Re

21、ference Pressure is a suitable se lected value for which test and performance data are given in Standards and to which the results of tests made at different barometric readings are corrected for purposes of compari son and standardization. 3-51 Range of Testing Pressure are values defining the rang

22、e of barometric conditions considered suitable for acceptance and check tests. Preferred Values 3-60 Standard Reference PressureThe reference value for barometric pressure has been estab lished at 29.92 inches (760 mm) of mercury, which corresponds to the average barometric pressure at sea level. (T

23、his value is universally recognized and established as the standard * Permits work in normally heated indoor spaces all year except 1 percent of time, depending on locality. This range is now specified in many electrical Standards. * Permits outdoor testing all except a small percentage of the year.

24、 * Narrower ranges for indoor and outdoor conditions where these may be desirable and applicable. reference in United States and International practice.) 3-61 Range of Testing PressureSince altitude is the main natural factor affecting air pressure, it is customary to specify a range of altitude for

25、 testing rather than air pressure. For pressures and altitudes encountered near the earths sur face, the preferred ranges for use are: 1st PreferenceSea level to 3300 feet (1000 meters) altitude, corresponding to average pressures of 29.92 inches (760 mm) to 26.53 inches (674 mm) of mercury. 2nd Pre

26、ferenceSea level to 6000 feet (1800 meters) altitude corresponding to average pressures of 29.92 inches (760 mm) to 23.98 inches (609 mm) of mercury. Test values obtained outside these ranges of conditions often can be made comparable by means of suitable correction factors, which cor rect to the St

27、andard Reference Pressure. Established practices in dealing with the effect of pressure and altitude vary with the nature of tests. In temperature rise tests on apparatus no corrections are made for altitudes in a specified range. In flashover and sparkover tests, corrections are made at all non-sta

28、nd ard pressures. For dielectric tests involving solid or liquid insulation only, pressure has a negligible effect. Also, where suitable correction factors have been estab lished, no limits are necessary. This permits obtaining comparable results at locations throughout the range of altitudes at the

29、 earths surface. Altitude Definitions 3-75 Standard Reference Altitude is a suitable se lected value for which performance data are given in Standards and which is established for purposes of standardization, particularly in the application of apparatus at different altitude levels. 3-76 Altitude Te

30、sting Range are values defining the range of altitudes considered suitable for acceptance and check tests. Preferred Values 3-80 Standard Reference AltitudeSea level is uni versally accepted as the reference value for alti tude. This value corresponds to the reference barometric pressure 29.92 inche

31、s (760 mm) of mercury. 3-81 Altitude Testing RangeWhere it is desirable to establish a range of altitude for testing pur poses, use, preferably, (a) Sea level to 3300 feet (1000 meters) alti tude. (b) Sea level to 6000 feet (1800 meters) alti tude. 4 The establishment of range (a) for tem perature r

32、ise and certain dielectric tests without correction factors is customary. Where suitable correction factors are available, no limits need be specified. Acceptance tests usually are made at manufacturing establishments or laboratories located at altitudes within this range. Range (b) includes most pl

33、aces on the earths surface where standard tests may be made. 3-82 Altitudes Above the Earths SurfaceDiffer ent groups have presented values for a standard atmosphere giving temperature, pressure and specific weight data of air for different altitudes above sea level. Table I extracted from the NACA

34、standard atmosphere data is typical. For additional data and the underlying assump tions and formulas, the NACA standard atmos phere is given in Tables 63 and 68, Smithsonian Meteorological Tables, 1951 edition, Smith sonian Institution, Washington, D. C. TABLE I Variation of Temperature Pressure an

35、d Density of Air with Altitude. Based on Average Conditions over U.S.A. at 40 Latitude. Relative Altitude Temperature Pressure Specific ft. C F In. mm Weight* 0 15* 59 29.92 760 1 1000 13 55 28.86 732 0.972 2000 11 52 27.82 706 0.943 3000 9 48 26.81 681 0.915 3300 8.5 47 26.53 674 0.908 4000 7 45 25

36、.84 656 0.888 5000 5 41 24.89 632 0.861 6000 3 38 23.98 609 0.836 8000 1 30 22.22 565 0.785 10000 5 23 20.58 523 0.738 12000 9 16 19.03 483 0.693 15000 14 6 16.88 429 0.628 18000 21 5 14.94 380 0.570 20000 24 12 13.75 350 0.533 25000 32 30 11.10 282 0.448 30000 44 48 8.88 226 0.374 35000 54 66 7.04

37、179 0.310 40000 55 67 5.54 141 0.244 50000 55 67 3.44 86 0.152 60000 55 67 2.13 54 0.094 65000 55 67 1.68 43 0.074 Relative Air Density 3-100 Relative Air DensityThe effects of tempera ture and pressure on the density of the air have been combined into a single factor known as “relative air density“

38、, which is unity for the standard conditions of temperature and pressure, 25 C (77 F) and 29.92 inches (760 mm) of mercury. For other conditions the relative air density is given by the formula 0.392 b (mm) 17.93 b (inches) * For relative air density based on 25C 77 F), the relative specific weight

39、should be multiplied by 1.035. 273 +1 (C) 459 +1 (F) in which b is barometric pressure and t is temperature. The quantity thus defined is strictly the density of a given mass of air relative to that of the same mass of air at standard pressure and tem perature and with the same content of water vapo

40、r. It does not indicate the true density of the gas which is influenced by water vapor content. 3-101 Corrections for Relative Air DensityRelative air density affects the electrical characteristics of air, particularly the flashover and sparkover of insulation and corona losses and radio influ ence

41、voltages on conductors. These quantities have been found to vary with relative air den sity to some power less than one. Windage losses in rotating machinery also vary with relative air density. In all cases, for the-small departures from unity usually encountered, values may be considered to vary d

42、irectly with the relative air density, and the relative density automatically includes altitude considerations through the medium of the barometric pres sure. For variations from unity relative air density greater than approximately 10 percent, it is sometimes desirable to specify correspond ing cor

43、rection factors as in Table II, AIEE Standard No. 4, Measurement of Voltage in Dielectric Tests. Where insulation temperatures are involved, it is on the other hand the practice to consider temperatures and altitudes separately. United States Weather Bureau data for the earths surface show an averag

44、e decrease of tempera ture of 0.55 C (1 F) for each 330 feet increase in altitude (Reference 3). HUMIDITY Definitions 3-150 Standard Reference Humidity is a suitable selected value for which performance data are given in records and Standards and to which results of tests made at different humiditie

45、s are corrected for purposes of comparison and stand ardization. 3-151 Range of Testing Humidity is the zone of humidity conditions considered suitable for ac ceptance and check tests. Humidity is designated in terms known as 5 Relative and Absolute humidity. Relative humid ity is the amount or pres

46、sure of water vapor in air at any given dry bulb temperature expressed as a percentage of the maximum amount or pressure of water vapor that the air can sustain at this temperature. Absolute humidity prefer ably is given as the pressure of water vapor in air in inches of mercury. Weight of water vap

47、or per unit volume in such units as grains per cubic foot or grams per cubic foot also has been used. The effects of humidity on electric apparatus and insulating materials are complex. Some phenomena correlate better for influence by using relative humidity, others by absolute humidity. In many cas

48、es exact relations have not been established, although variations have been observed. The electric breakdown of air in non-homogeneous electric fields varies with humidity, and correction factors have been evaluated and correlated for values of absolute humidity for many types of apparatus. On the o

49、ther hand, the conditioning of insulating mate rials for test, the testing of finishes, cements and adhesives are generally based on values of relative humidity. Therefore, it is necessary to recognize these practical conditions by estab lishing reference and limiting values for both absolute and relative humidity. Absolute Humidity Preferred Values 3-160 Standard Reference Absolute HumidityThe reference value for absolute humidity in com mon use in the United States for dielectric tests is 0.608S inch (15.45 mm) mercury vapor pr