1、BRITISH STANDARDBS EN 61788-2:2007Superconductivity Part 2: Critical current measurement DC critical current of Nb3Sn composite superconductorsThe European Standard EN 61788-2:2007 has the status of a British StandardICS 17.220; 29.050g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3
2、g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58BS EN 61788-2:2007This British Standard was published under the authority of the Standards Policy and Strategy Committee on 28 February 2007 BSI 2007ISBN 978 0 580 5
3、0219 4National forewordThis British Standard was published by BSI. It is the UK implementation of EN 61788-2:2007. It is identical with IEC 61788-2:2006. It supersedes BS EN 61788-2:1999 which is withdrawn.The UK participation in its preparation was entrusted to Technical Committee L/-/90, Supercond
4、uctivity.A list of organizations represented on L/-/90 can be obtained on request to its secretary.This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application.Compliance with a British Standard cannot confer immunity from
5、 legal obligations. Amendments issued since publicationAmd. No. Date CommentsEUROPEAN STANDARD EN 61788-2 NORME EUROPENNE EUROPISCHE NORM January 2007 CENELEC European Committee for Electrotechnical Standardization Comit Europen de Normalisation Electrotechnique Europisches Komitee fr Elektrotechnis
6、che Normung Central Secretariat: rue de Stassart 35, B - 1050 Brussels 2007 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members. Ref. No. EN 61788-2:2007 E ICS 17.220; 29.050 Supersedes EN 61788-2:1999English version Superconductivity Part 2: Crit
7、ical current measurement - DC critical current of Nb3Sn composite superconductors (IEC 61788-2:2006) Supraconductivit Partie 2: Mesure du courant critique - Courant critique continu des supraconducteurs composites Nb3Sn (CEI 61788-2:2006) Supraleitfhigkeit Teil 2: Messen des kritischen Stromes - Kri
8、tischer Strom (Gleichstrom) von Nb3Sn-Verbundsupraleitern (IEC 61788-2:2006) This European Standard was approved by CENELEC on 2006-12-01. CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a na
9、tional standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CENELEC member. This European Standard exists in three official versions (English, French, German). A version
10、 in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the Central Secretariat has the same status as the official versions. CENELEC members are the national electrotechnical committees of Austria, Belgium, Cyprus, the Czech Repu
11、blic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom. EN 61788-2:2007 2 Foreword The text of document
12、 90/195/FDIS, future edition 2 of IEC 61788-2, prepared by IEC TC 90, Superconductivity, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as EN 61788-2 on 2006-12-01. This European Standard supersedes EN 61788-2:1999. Modifications made to EN 61788-2:1999 are mostly wording
13、 that essentially includes no technical changes and an addition of a new annex (normative Annex D) in which the specifications in the one-mandrel method are described. The following dates were fixed: latest date by which the EN has to be implemented at national level by publication of an identical n
14、ational standard or by endorsement (dop) 2007-09-01 latest date by which the national standards conflicting with the EN have to be withdrawn (dow) 2009-12-01 Annex ZA has been added by CENELEC. _ Endorsement notice The text of the International Standard IEC 61788-2:2006 was approved by CENELEC as a
15、European Standard without any modification. 3 EN 61788-2:2007 CONTENTS INTRODUCTION.5 1 Scope 6 2 Normative references .6 3 Terms and definitions .7 4 Principle.8 5 Requirements.8 6 Apparatus.9 6.1 Reaction mandrel material .9 6.2 Reaction mandrel construction.9 6.3 Measurement mandrel material 10 6
16、.4 Measurement mandrel construction10 6.5 Measurement set up 10 7 Specimen preparation.10 7.1 Specimen mounting for reaction heat treatment10 7.2 Reaction heat treatment 11 7.3 Specimen mounting for measurement 11 7.4 Specimen bonding .11 8 Measurement procedure .12 9 Precision and accuracy of the t
17、est method 13 9.1 Critical current.13 9.2 Temperature13 9.3 Magnetic field13 9.4 Specimen support structure .13 9.5 Specimen protection 13 10 Calculation of results 14 10.1 Critical current criteria .14 10.2 n-value (optional calculation, refer to A.7.2) .15 11 Test report .15 11.1 Identification of
18、 test specimen15 11.2 Report of Icvalues 15 11.3 Report of test conditions 16 Annex A (informative) Additional information relating to Clauses 1 to 10 .17 Annex B (informative) Strain effect of Nb3Sn conductors 29 Annex C (informative) Self-field effect 31 Annex D (normative) One-mandrel method .33
19、Annex ZA (normative) Normative references to international publications with their corresponding European publications37 Bibliography .36 EN 61788-2:2007 4 Figure 1 Intrinsic U-I characteristic .14 Figure 2 U-I characteristic with a current transfer component 14 Figure A.1 Instrumentation of specime
20、n with a null voltage tap pair.22 Figure B.1 Uniaxial (tensile) strain dependence of critical current for a typical Nb3Sn composite wire shown with various magnetic fields 7.30 Table A.1 Thermal contraction data of Nb3Sn superconductor and selected materials .28 5 EN 61788-2:2007 INTRODUCTION The cr
21、itical currents of composite superconductors are used to establish design limits for applications of superconducting wires. The operating conditions of superconductors in these applications determine much of their behaviour and tests made with the method given in the present standard may be used to
22、provide part of the information needed to determine the suitability of a specific superconductor. Results obtained from this method may also be used for detecting changes in the superconducting properties of a composite superconductor due to processing variables, handling, ageing or other applicatio
23、ns or environmental conditions. This method is useful for quality control, acceptance or research testing if the precautions given in this standard are observed. The critical current of composite superconductors depends on many variables. These variables need to be considered in both the testing and
24、 the application of these materials. Test conditions such as magnetic field, temperature and relative orientation of the specimen, current and magnetic field are determined by the particular application. The test configuration may be determined by the particular conductor through certain tolerances.
25、 The specific critical current criterion may be determined by the particular application. It may be appropriate to measure a number of test specimens if there are irregularities in testing. The test method covered in this standard is based on that for the determination of the critical current of Cu/
26、Nb-Ti composite superconductors (IEC 61788-12 1)and the VAMAS (Versailles project on advanced materials and standards) prestandardization work on the critical current of Nb3Sn composite superconductors. The critical current of Nb3Sn superconductors is known to be highly sensitive to mechanical strai
27、n compared to Cu/Nb-Ti superconductors. Hence, some modifications are made on the test procedures which may affect the strain state of a test specimen. See Annex B for the background to these modifications. 1)Figures in square brackets refer to the Bibliography. EN 61788-2:2007 6 SUPERCONDUCTIVITY P
28、art 2: Critical current measurement DC critical current of Nb3Sn composite superconductors 1 Scope This part of IEC 61788 covers a test method for the determination of the d.c. critical current of Nb3Sn composite superconductors which are fabricated by either the bronze process or the internal tin d
29、iffusion process and have a copper/non-copper ratio larger than 0,2. This method is intended for use with superconductors which have critical currents of less than 1 000 A and n-values larger than 12 under standard test conditions and at magnetic fields of less than or equal to 0,7 times the upper c
30、ritical magnetic field. The test specimen is immersed in a liquid helium bath at a known temperature during testing. The Nb3Sn composite test conductor has a monolithic structure with a total round-cross-sectional area that is less than 2 mm2. The specimen geometry used in this test method is an ind
31、uctively coiled specimen. Deviations from this test method which are allowed for routine tests and other specific restrictions are given in this standard. Nb3Sn conductors with critical currents above 1 000 A or total cross-sectional areas greater than 2 mm2can be measured with the present method wi
32、th an anticipated reduction in precision and a more significant self-field effect (see Annex C). Other, more specialized, specimen test geometries may be more appropriate for larger conductor testing which have been omitted from this present standard for simplicity and to retain precision. The test
33、method given in this standard should in principle apply to Nb3Sn composite wires fabricated by any other process. This method is also expected to apply to other superconducting composite wires after some appropriate modifications. 2 Normative references The following referenced document is indispens
34、able for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60050-815:2000, International Electrotechnical Vocabulary (IEV) Part 815: Superconductivity 7
35、 EN 61788-2:2007 3 Terms and definitions For the purposes of this document, the terms and definitions given in IEC 60050-815, some of which are repeated here for convenience, and the following apply: 3.1 critical current Icmaximum direct current that can be regarded as flowing without resistance NOT
36、E Icis a function of magnetic field strength and temperature. IEV 815-03-01 3.2 critical current criterion Iccriterion criterion to determine the critical current, Ic, based on the electric field strength, E, or the resistivity, NOTE E = 10 V/m or E = 100 V/m is often used as the electric field stre
37、ngth criterion, and = 10-13m or = 10-14 m is often used as the resistivity criterion. IEV 815-03-02 3.3 n-value (of a superconductor) exponent obtained in a specific range of electric field strength or resistivity when the voltage (U) current (I) curve is approximated by the equation U InIEV 815-03-
38、10 3.4 quench uncontrollable and irreversible transition of a superconductor or a superconducting device from the superconducting state to the normal state NOTE A term usually applied to superconducting magnets. IEV 815-03-11 3.5 Lorentz force (on fluxons) force applied to fluxons by a current NOTE
39、1 The force per unit volume is given by J x B, where J is the current density, and B is the magnetic flux density. IEV 815-03-16 NOTE 2 “Coulomb-Lorentz force“ is defined in IEV 121-11-20 1. 3.6 stress effect strain effect change in superconducting properties upon application of mechanical, thermal
40、or electro-magnetic stress to the superconductor IEV 815-03-14 EN 61788-2:2007 8 3.7 bending strain bstrain in percent arising from pure bending defined as b= 100r/R, where r is a half of the specimen thickness and R is the bending radius IEV 815-08-03 3.8 current transfer (of composite superconduct
41、or) phenomenon that a d.c. current transfers spatially from filament to filament in a composite superconductor, resulting in a voltage generation along the conductor NOTE In the Icmeasurement, this phenomenon appears typically near the current contacts where the injected current flows along the cond
42、uctor from periphery to inside until uniform distribution among filaments is accomplished. 3.9 constant sweep rate method U-I data acquisition method where a current is swept at a constant rate from zero to a current above Icwhile frequently and periodically acquiring U-I data 3.10 ramp-and-hold met
43、hod U-I data acquisition method where a current is ramped to a number of appropriately distributed points along the U-I curve and held constant at each one of these points while acquiring a number of voltages and current readings 4 Principle The critical current of a composite superconductor is dete
44、rmined from a voltage (U) current (I) characteristic measured at a certain value of a static applied magnetic field strength (magnetic field) at a specified temperature in a liquid helium bath at a constant pressure. To get a U-I characteristic, a direct current is applied to the superconductor spec
45、imen and the voltage generated along a section of the specimen is measured. The current is increased from zero and the U-I characteristic generated is recorded. The critical current is determined as the current at which a specific electric field strength (electric field) criterion (Ec) or resistivit
46、y criterion (c) is reached. For either Ecor c, there is a corresponding voltage criterion (Uc) for a specified voltage tap separation. 5 Requirements The specimen shall be wound on a cylindrical reaction mandrel with a helical groove and after reaction, transferred to a measurement mandrel of the sa
47、me diameter on which the helical angle is preserved. An alternate one-mandrel method is given in Annex D. The specimen shall be longer than 430 mm. The specimen shall be affixed to the measurement mandrel by tightening the specimen and/or bonding with a low temperature adhesive. In this test method,
48、 the applied magnetic field shall be parallel to the measurement mandrel axis. 9 EN 61788-2:2007 The target precision of this method is a coefficient of variation (standard deviation divided by the average of the critical current determinations), that is less than 3 % for the measurement at 12 T and
49、 near 4,2 K. The use of a common current transfer correction is excluded from this test method. Furthermore, if a current transfer signature is pronounced in the measurement, then the measurement shall be considered invalid. It is the responsibility of the user of this standard to consult and establish appropriate safety and health practices, and determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given below. H
