1、IEEE Std C57.144-2004IEEE StandardsC57.144TMIEEE Guide for Metric Conversion ofTransformer Standards3 Park Avenue, New York, NY 10016-5997, USAIEEE Power Engineering SocietySponsored by theTransformers CommitteeIEEE Standards22 October 2004Print: SH95259PDF: SS95259Recognized as anAmerican National
2、Standard (ANSI)The Institute of Electrical and Electronics Engineers, Inc.3 Park Avenue, New York, NY 10016-5997, USACopyright 2004 by the Institute of Electrical and Electronics Engineers, Inc.All rights reserved. Published 22 October 2004. Printed in the United States of America.IEEE is a register
3、ed trademark in the U.S. Patent (978) 750-8400. Permission to photocopy portions of any individual standard for educationalclassroom use can also be obtained through the Copyright Clearance Center.Note: Attention is called to the possibility that implementation of this standard may require use of su
4、bject mat-ter covered by patent rights. By publication of this standard, no position is taken with respect to the existence orvalidity of any patent rights in connection therewith. The IEEE shall not be responsible for identifying patentsfor which a license may be required by an IEEE standard or for
5、 conducting inquiries into the legal validity orscope of those patents that are brought to its attention.Copyright 2004 IEEE. All rights reserved. iiiIntroduction(This introduction is not part of IEEE Std C57.144-2004, IEEE Guide for Metric Conversion of Transformer Standards.)In 1995, IEEE implemen
6、ted a new metric policy (IEEE Policy 9.20), which directed that all IEEE publica-tions undergo a transition from U.S. Customary (or inch-pound) units of measure to metric or Le SystmeInternational dUnits (SI). The metric or SI system is the standard for science and engineering and in com-mon usage i
7、n nearly all countries of the world except for the United States. The IEEE Policy directed thatstandards published after January 2000 were to be expressed solely in metric units.Subsequently, the IEEE-SA Standards Board modified the policy on 11 September 2003 to allow somelatitude in conversion fro
8、m U.S. Customary to metric units. The revised policy is identified as Policy 9.19.The new policy states that standards should use metric units exclusively in the normative portions of thestandard, but the use of metric units with parenthetical inch-pound units are also permitted.Working groups and s
9、ubcommittees of the IEEE Transformers Committee tried to make these conversions,but when the work of one body was compared with another, it was found that conversions were often madeeither inconsistently or incorrectly. The existing guide, IEEE/ASTM SI 10TM-2002 and its predecessor,IEEE Std 268TM-19
10、92, were not being used as intended. Both documents are listed here because someimportant information regarding conversion of toleranced values has been omitted from the more recentguide. The Transformers Committee formed a Metric Conversion Task Force to address the problemsencountered by the worki
11、ng groups in revising their standards. The Task Force presented tutorials for Trans-formers Committee members and is hereby creating an IEEE guide to create a better understanding of metricusage and of conversion methods as they apply to Transformer Standards.Notice to usersErrataErrata, if any, for
12、 this and all other standards can be accessed at the following URL: http:/standards.ieee.org/reading/ieee/updates/errata/index.html. Users are encouraged to check this URL forerrata periodically.InterpretationsCurrent interpretations can be accessed at the following URL: http:/standards.ieee.org/rea
13、ding/ieee/interp/index.html.PatentsAttention is called to the possibility that implementation of this standard may require use of subject mattercovered by patent rights. By publication of this standard, no position is taken with respect to the existence orvalidity of any patent rights in connection
14、therewith. The IEEE shall not be responsible for identifyingpatents or patent applications for which a license may be required to implement an IEEE standard or forconducting inquiries into the legal validity or scope of those patents that are brought to its attention.iv Copyright 2004 IEEE. All righ
15、ts reserved.ParticipantsThe following is a list of participants in the Guide to Metric Conversion Working Group.Dudley L. Galloway, ChairTimothy W. Olson, Vice-ChairThe following members of the individual balloting committee voted on this guide. Balloters may have votedfor approval, disapproval, or
16、abstention. Gene BlackburnJohn BorstTommy CooperMichael CulhaneAli GhafourianBrian KaplonskiGael R. KennedyRon KirkerMichael MitelmanDaniel MulkeyRobert OlenEdwin OwenThomas PekarekStephen ShullRonald StaharaDonnie TrivittDavid AhoStan J. ArnotPeter M. BalmaRonald BarkerW. J. (Bill) BergmanEdward Be
17、rtoliniWallace BinderThomas E. Blackburn IIIWilliam BoettgerAlain BolligerJohn BorstCarl BushThomas CallsenMax CambreTommy CooperMichael CulhaneR. DaubertGuru Dutt DhingraWilliam DarovnyAlan DarwinByron DavenportPranathy DineshDieter DohnalAmir El-SheikhFred ElliottGary EngmannMehrdad EskandaryJorge
18、 Fernandez-DaherJoseph FoldiBruce ForsythMarcel FortinDerek FosterDudley GallowayWilliam GriesackerRandall GrovesErik GuillotBal GuptaMichael HaasRoger HayesAjit HiranandaniEdward Horgan, Jr.James D. Huddleston IIIRowland James, Jr.Charles JohnsonJoseph KellyGael R.KennedySheldon KennedyTanuj Khande
19、lwalBoyd LeuenbergerDonald LoweGregory LuriAl MaguireWilliam MajeskiJ. Dennis MarlowJohn MatthewsLee MatthewsSusan McNellyNigel McQuinJoseph MelansonG. MichaelDan MulkeyJerry MurphyRichard MusilKrste NajdenkoskiJeffrey NelsonJoe NimsT. W. OlsenThomas PekarekPaul PillitteriDonald PlattsAlvaro Portill
20、oCharles RaymondJohannes RickmannPeter RisseOleg RoizmanJohn RossettiJames RuggieriSurya SantosoDevki SharmaStephen ShullH. Jin SimJames E. SmithJames E. SmithJerry SmithThomas SpitzerAllan St. PeterRonald StaharaPeter StewartJohn TeixeiraMalcolm V. ThadenJuan Luis ThierryThomas TraubAlan TrautJohn
21、VandermaarJoe WatsonAlan WilksJames WilsonWilliam WimmerCopyright 2004 IEEE. All rights reserved. vWhen the IEEE-SA Standards Board approved this guide on 24 June 2004, it had the following membership:Don Wright, ChairSteve M. Mills, Vice ChairJudith Gorman, Secretary*Member EmeritusAlso included ar
22、e the following nonvoting IEEE-SA Standards Board liaisons:Satish K. Aggarwal, NRC RepresentativeRichard DeBlasio, DOE RepresentativeAlan Cookson, NIST RepresentativeSavoula AmanatidisIEEE Standards Managing EditorChuck AdamsH. Stephen BergerMark D. BowmanJoseph A. BruderBob DavisRoberto de BoissonJ
23、ulian Forster*Arnold M. GreenspanMark S. HalpinRaymond HapemanRichard J. HollemanRichard H. HulettLowell G. JohnsonJoseph L. Koepfinger*Hermann KochThomas J. McGeanDaleep C. MohlaPaul NikolichT. W. OlsenRonald C. PetersenGary S. RobinsonFrank StoneMalcolm V. ThadenDoug ToppingJoe D. Watsonvi Copyrig
24、ht 2004 IEEE. All rights reserved.Contents1. Overview 11.1 Scope 11.2 Purpose. 12. References 13. Guidelines 23.1 Application of converted values 23.2 “Hard” and “soft” conversion 23.3 Use convenient numbers 23.4 Convert fractions 23.5 Determine tolerance . 23.6 Maintain original minimums and maximu
25、ms 23.7 Significant digits should be less than 10% of the overall tolerance 33.8 Method for conversion of toleranced values 33.9 Gauge and absolute pressure 33.10 Maintain significant digits . 33.11 The precision of a value. 43.12 Trade sizes . 43.13 Standard for rounding 43.14 Conversion math 43.15
26、 Writing unit symbols . 43.16 Capitalization . 43.17 Units of force and mass . 43.18 Specifying a quantity with a tolerance. 53.19 Dual dimensioning . 53.20 Temperature conversion 53.21 Default tolerances 53.22 Convenience and drawing clarity 53.23 Separate + and tolerances . 63.24 Safety issues. 6A
27、nnex A (normative) Conversion of quantities common to transformer standards 7Annex B (normative) Guideline background and development 9Annex C (informative) Bibliography. 11Copyright 2004 IEEE. All rights reserved. 1IEEE Guide for Metric Conversion of Transformer Standards1. Overview1.1 ScopeThe int
28、ent of this guide is to assist the working groups within the IEEE Transformers Committee; thus,specific examples were taken from the transformer-related standards. It should be recognized thatidentification of general principles and procedures could have broader application.1.2 PurposeThe purpose of
29、 this guide is to assist Transformer Working Groups in the interpretation of IEEE/ASTM SI 10TM-20021and other appropriate standards as they convert their documents to the use of SI units.This guide is concerned only with the conversion of existing standards, where a manufacturers product thatmeets t
30、he existing standards limits in U.S. Customary units will always meet the new standards limits in SIunits. With the exception of a few very specific examples in A.3, there has been no attempt to make themetric values more rounded or more convenient. Making such changes to a standard may affect thequ
31、alification of existing designs and should come only from a consensus of the interested parties in theappropriate working groups.2. ReferencesThis guide shall be used in conjunction with the following standard.IEEE/ASTM SI 10-2002, American National Standard for Use of the International System of Un
32、its (SI):The Modern Metric System.21Information on references can be found in Clause 2.2IEEE publications are available from the Institute of Electrical and Electronics Engineers, Inc., 445 Hoes Lane, Piscataway, NJ 08854,USA (http:/standards.ieee.org/).IEEEStd C57.144-2004 IEEE GUIDE FOR METRIC CON
33、VERSION OF TRANSFORMER STANDARDS2 Copyright 2004 IEEE. All rights reserved.3. Guidelines3.1 Application of converted valuesEnsure converted values do not suggest a precision (repeatability or confidence interval) that you do notneed or cannot measure. For example, the precision of a tape measure or
34、other manual measuring method islimited to about 1/32 in (0.031 in) or 1 mm (0.039 in).3.2 “Hard” and “soft” conversionAlthough the use of these terms is not recommended, the concepts should be understood: “Soft” conversionis a statement of mathematical identity, without regard to significant digits
35、. For example, a soft conversionof 100 ft = 30.480 m. A “hard” conversion, on the other hand, will be rounded to a more convenient valuethat is easy to work with, such as 100 ft = 30.5 m. Hard conversions may maintain a consistent number ofsignificant digits in both values, but the definition does n
36、ot specifically state this possibility (seeSmith B4).33.3 Use convenient numbersOverall, 16.5 L/s is handier than 1.65 E-02 m3/s. The liter (or litre) is equal to 0.001 m3and is recommendedfor common volumes where the use of m3is unwieldy. For such volumes, use the symbols “L,” “mL,” and“L” only. Do
37、 not use units such as “cm3”.3.4 Convert fractionsDimensions presently in fractional inches should be expressed as decimals to a reasonable level of precisionprior to any conversion. Where a prior conversion from fractions is suspected, an exact conversion may havekept excessive decimal places, over
38、stating the precision attainable. For example, a dimension now shown as0.1875 in probably originated as 3/16 in and should have been expressed as 0.19 in when first decimalized.3.5 Determine toleranceBefore any conversion, try to determine the stated, implied, or inherent tolerance on the quantity.
39、Thistolerance may depend on the available measurement methods or on the typical manufacturing technologyused. For example, the typical manufacturing tolerance for linear dimensions for sand-casting with acopper alloy is 1/32 in 0.031 in 0.8 mm.3.6 Maintain original minimums and maximumsDo not violat
40、e original minimum and maximum values when converting without considering theconsequences. For mating parts that must fit together, expanding a tolerance limit can have severeconsequences. For situations where mating parts are not involved, the expansion of tolerances by smallamounts, e.g., fraction
41、s of a millimeter, will probably be inconsequential.3The numbers in brackets correspond to those of the bibliography in Annex C.IEEEIEEE GUIDE FOR METRIC CONVERSION OF TRANSFORMER STANDARDS Std C57.144-2004Copyright 2004 IEEE. All rights reserved. 33.7 Significant digits should be less than 10% of t
42、he overall toleranceThis general rule for “10% accuracy in the rounding of tolerances” is arbitrary, but it works well for theapplications considered here. This rule is the basis for Table C.1 in IEEE Std 268TM-1992 B2 used for con-verting tolerances in inches to millimeters. This table is repeated
43、in B.4 for convenience. The “10%accuracy” chart states that any total tolerance 0.4 in should produce values rounded to the nearest 1 mm,which is consistent with 3.1.Another source is F2.4 of CSA Z234.1-2000 B1, which shows how to calculate the rounding fineness forconversion of any units to any pre
44、cision. Annex B of this guide has the background for development of“fineness of rounding” limits used herein.3.8 Method for conversion of toleranced valuesOnce the “fineness of rounding” is established, the conversion of a toleranced value in one system can beconverted to another as illustrated with
45、 the following example:To convert a pressure of 200 15 psi using a 10% accuracy of agreement:a) Determine total tolerance; total tolerance is 15 psi or a total of 30 psi.b) Find conversion factor: to convert pound-force per square inch (psi) to kilopascal (kPa), multiply by6.894757.c) Convert 10% of
46、 the total tolerance; 10% of 30 psi is 3 psi. 3 6.8948 = 20.68 kPa.d) To be less than 10%, both the nominal value and the tolerance value must be expressed to the nearest10 kPa because 100 20.68 but 10 =IEEEStd C57.144-2004 IEEE GUIDE FOR METRIC CONVERSION OF TRANSFORMER STANDARDS10 Copyright 2004 I
47、EEE. All rights reserved.Thus, for 0.04 T 0.4 and a 10% accuracy of rounding, the nominal value and tolerance in millimetersshould be rounded to the precision value greater than or equal to 0.10 mm and less than 1.0 mm, that is,rounded to the nearest 0.1 mm.B.4 Table for conversion of tolerancesThe
48、following example demonstrates the method for rounding presented in B.3 applied to transformer com-ponents. Bushing spacings are given as 6.5 in, 4.5 in, and 6.0 in, with a standard tolerance of 0.25 in. Thetotal tolerance is 0.5 in, which implies a fineness of 1 mm, according to Table B.1.The conve
49、rted limits of 6.5 0.25 in are 158.75 mm and 171.45 mm. The nominal value converts toexactly 165.1 mm with a tolerance of 6.35 mm. When rounded to 1 mm, the conversion yields165 6 mm. In this case, the tolerance is rounded down so the original limits are not exceeded. Similarly,4.5 0.25 in = 114 6 mm and 6.0 0.25 in = 152 6 mm. In this last example, the lower limit,146 mm, is 5.7480 in, which is 0.002 in outside the original lower limit. This small discrepancy is unlikelyto cause any problem.Table B.1Inches to millimeters
