1、BRITISH STANDARDBS EN 61788-9:2005Superconductivity Part 9: Measurements for bulk high temperature superconductors Trapped flux density of large grain oxide superconductorsThe European Standard EN 61788-9:2005 has the status of a British StandardICS 17.220; 29.050g49g50g3g38g50g51g60g44g49g42g3g58g4
2、4g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58BS EN 61788-9:2005This British Standard was published under the authority of the Standards Policy and Strategy Committee on 24 January 2
3、006 BSI 24 January 2006ISBN 0 580 46887 9National forewordThis British Standard is the official English language version of EN 61788-9:2005. It is identical with IEC 61788-9:2005.The UK participation in its preparation was entrusted to Technical Committee L/-/90, Superconductivity, which has the res
4、ponsibility to: A list of organizations represented on this committee can be obtained on request to its secretary.Cross-referencesThe British Standards which implement international or European publications referred to in this document may be found in the BSI Catalogue under the section entitled “In
5、ternational Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online.This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a
6、British Standard does not of itself confer immunity from legal obligations. aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep UK interests informed; monitor related international an
7、d European developments and promulgate them in the UK.Summary of pagesThis document comprises a front cover, an inside front cover, the EN title page, pages 2 to 20, an inside back cover and a back cover.The BSI copyright notice displayed in this document indicates when the document was last issued.
8、Amendments issued since publicationAmd. No. Date CommentsEUROPEAN STANDARD EN 61788-9 NORME EUROPENNE EUROPISCHE NORM August 2005 CENELEC European Committee for Electrotechnical Standardization Comit Europen de Normalisation Electrotechnique Europisches Komitee fr Elektrotechnische Normung Central S
9、ecretariat: rue de Stassart 35, B - 1050 Brussels 2005 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members. Ref. No. EN 61788-9:2005 E ICS 17.220; 29.050 English version Superconductivity Part 9: Measurements for bulk high temperature superconduct
10、ors - Trapped flux density of large grain oxide superconductors (IEC 61788-9:2005) Supraconductivit Partie 9: Mesures pour supraconducteurs haute temprature massifs Densit de flux rsiduel des oxydes supraconducteurs gros grains (CEI 61788-9:2005) Supraleitfhigkeit Teil 9: Messungen an massiven Hocht
11、emperatursupraleitern - Eingefrorene magnetische Flussdichte bei grobkrnigen oxidischen Supraleitern (IEC 61788-9:2005) This European Standard was approved by CENELEC on 2005-06-01. CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for givin
12、g this European Standard the status of a national 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 ve
13、rsions (English, French, German). A version 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
14、of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom. Foreword The text of docu
15、ment 90/167/FDIS, future edition 1 of IEC 61788-9, prepared by IEC TC 90, Superconductivity, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as EN 61788-9 on 2005-06-01. The following dates were fixed: latest date by which the EN has to be implemented at national level by
16、publication of an identical national standard or by endorsement (dop) 2006-03-01 latest date by which the national standards conflicting with the EN have to be withdrawn (dow) 2008-06-01 Annex ZA has been added by CENELEC. _ Endorsement notice The text of the International Standard IEC 61788-9:2005
17、was approved by CENELEC as a European Standard without any modification. _ EN 61788-9:2005 2 3 EN 61788-9:2005 CONTENTS INTRODUCTION.4 1 Scope 5 2 Normative references .5 3 Terms and definitions .5 4 Principle.5 5 Requirements.7 6 Apparatus.8 7 Measurement procedure .9 8 Precision and accuracy of th
18、e test method 9 9 Test report .10 Annex A (informative) Additional information related to Clauses 3 to 6 11 Annex B (informative) Measurements for levitation force of bulk high temperature superconductors .14 Annex C (informative) Test report (example) 17 Annex ZA (normative) Normative references to
19、 international publications with their corresponding European publications. 20 Bibliography .19 Figure 1 Principle of trapped flux density in bulk superconductor.6 Figure 2 Schematic view of the experimental set-up.7 Figure A.1 Thickness dependence of the trapped flux density (Bz) 11 Figure A.2 Gap
20、dependence of the field strength 13 Figure C.1 Distribution map of trapped flux density .18 EN 61788-9:2005 4 INTRODUCTION Large grain bulk high temperature superconductors (BHTSC) have significant potential for a variety of engineering applications, such as magnetic bearings, flywheel energy storag
21、e systems, load transports, levitation, and trapped flux density magnets. Large grain superconductors have already been brought to market worldwide. For industrial applications of bulk superconductors, there are two important material properties. One is the magnetic levitation force, which determine
22、s the tolerable weight supported by a bulk superconductor. The other is the trapped flux density, which determines the maximum field that a bulk superconductor can generate. The users of bulk superconductors must know these values for the design of their devices. However, these values are strongly d
23、ependent on the testing method, and therefore it is critically important to set up an international standard for the determination of these values both for manufacturers and industrial users. The test method covered in this standard is based on the VAMAS (Versailles Project on Advanced Materials and
24、 Standards) pre-standardization work on the properties of bulk high temperature superconductors. 5 EN 61788-9:2005 SUPERCONDUCTIVITY Part 9: Measurements for bulk high temperature superconductors Trapped flux density of large grain oxide superconductors 1 Scope This part of IEC 61788 specifies a tes
25、t method for the determination of the trapped field (trapped flux density) of bulk high temperature superconductors. This International Standard is applicable to large grain bulk oxide superconductors that have well defined shapes such as round discs, rectangular, and hexagonal pellets. The trapped
26、flux density can be assessed at temperatures from 4,2 K to 90 K. For the purpose of standardization, the trapped flux density will be reported for liquid nitrogen temperature. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated
27、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 Part 815: Superconductivity3 Terms and definitions For the purposes of this document, t
28、he terms and definitions given in IEC 60050(815) and the following apply. 3.1 trapped flux density strength of the magnetic flux density (T) trapped by a bulk high temperature superconductor (BHTSC) at a defined gap and at a defined temperature 3.2 maximum trapped flux density peak value of the trap
29、ped flux density NOTE For most measurements, only the z component of the flux density is measured, which is strongly affected by the sample geometry or the demagnetizing effect (see Clause A.2). Thus the total flux density, which is the integration of all the field components, may also be regarded a
30、s the materials property to stand for the trapped flux density (see Clause A.1). 4 Principle Superconductors that exhibit flux pinning are capable of trapping magnetic fields, as shown in Figure 1. Here the internal magnetic flux density rotation ( B ) in the BHTSC is proportional to the critical cu
31、rrent density (Jc), as expressed by the following equation: c0JB = EN 61788-9:2005 6 In one dimension, the equation is reduced to yzJxBc0dd = in rectangular coordinates or to c0dd JrBz= in cylindrical coordinates. The maximum value of the trapped flux density in the z component (Bz,max) in an infini
32、te cylinder (2 R in diameter) is given by the following equation: RJBzc0max,= In practical samples, this value is reduced by the demagnetizing effect or the geometrical effect as follows: RJtRDBzc0max,)/( = where D(R/t) is a geometrical constant that depends on the shape (the ratio of radius/thickne
33、ss) of the BHTSC. Bzx dBz/dx = JcyIEC 557/05 Figure 1 Principle of trapped flux density in bulk superconductor 7 EN 61788-9:2005 Figure 2 shows a schematic diagram of the experimental set-up for trapped flux density measurements 11). There are several ways to measure the trapped flux density of BHTS
34、C. A typical measurement procedure is as follows. Firstly, the field is applied on the superconductor. Secondly, the sample is fixed on the cold head of a cryostat, which is cooled to the target temperature by using a cooling device. After reaching the target temperature, the external field is remov
35、ed. The distribution of the field trapped by the BHTSC is then measured by scanning a Hall sensor over the specimen surface at a defined gap. This is the so-called field-cooled (FC) method of magnetization. y x Hall sensor SuperconductorSuperconducting magnet Cryostat z x IEC 558/05 Figure 2 Schemat
36、ic view of the experimental set-up 5 Requirements Upon removal of the external field, the trapped flux density will decay with time from its initial value. This is due initially to flux flow and later to flux creep (collectively termed flux relaxation). The initial peak value shall not be used for t
37、he design of machines. The trapped flux density values are those measured after a sufficiently long time has passed since the appropriate measurement conditions were reached. The trapped flux density values shall be measured at least 15 min after the external field is removed from the specimen under
38、 test. The target precision of this method is that the coefficient of variation in any inter-comparison test shall be 5 % or less for measurements performed within 1 month of each other 2. It is the responsibility of the user of this standard to consult and establish appropriate safety and health pr
39、actices and to determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given below. 1)Figures in square brackets refer to the bibliography. EN 61788-9:2005 8 Hazards exist in this type of measurement. Very large direct currents with very low voltages
40、 do not necessarily provide a direct personal hazard, but strong magnetic fields trapped by the BHTSC may cause the problem. It is imperative to shield magnetic fields. Also the energy stored in the superconducting magnets commonly used for generating the magnetic field can cause large current and/o
41、r voltage pulses, or deposit a large amount of thermal energy in the cryogenic systems causing rapid boil-off or even explosive conditions. Direct contact of skin with cold liquid transfer lines, storage dewars or apparatus components can cause immediate freezing, as can direct contact with a spille
42、d cryogen. It is imperative that safety precautions for handling cryogenic liquids be observed. 6 Apparatus 6.1 Cryostat The cryostat shall include a BHTSC specimen support and a liquefied cryogen reservoir for the measurements. Other cooling devices can also be used for the temperature control of t
43、he specimens. Before measurements, the specimen shall be held at the measured temperature for a sufficient amount of time to cool, since large grain BHTSC specimens in typical size (greater than 3 cm in diameter) require a long time for the entire body to reach the target temperature. The recommende
44、d waiting time can be estimated by considering the size and thermal conductivity coefficient of the BHTSC. For a large grain BHTSC, the temperature tends to increase during the measurements, so the power of the cooling device shall be large enough to avoid a temperature rise of the specimen. 6.2 Act
45、ivation magnet In principle, any activation magnet or a magnetizing device can be used as long as the trapped flux density is saturated (see Clause A.3). The activation magnet shall have a working area larger than the dimension of BHTSC. The magnetizing field required to saturate the field trapping
46、ability of BHTSC is determined by the demagnetizing factor of the sample (see Clause A.3). If the field strength of the activation magnet is high enough, the applied field does not need to be uniform. Pulse field activation is not recommended for standardization, since the error associated with this
47、 magnetization process is very large and its results are generally non-reproducible. 6.3 Support of BHTSC During trapped flux density measurements, large electromagnetic forces will act on the BHTSC. Therefore, the BHTSC shall be firmly fixed to the support, which shall be non-magnetic and have a hi
48、gh enough mechanical strength to withstand the electromagnetic force. The BHTSC shall be fixed to the support, in most cases, with materials that harden at low temperatures. If the uniformity of the BHTSC is sufficiently good with the c-axis aligned to the external field, the measurements can be per
49、formed by simply placing the BHTSC on a non-magnetic substrate. Due to the large anisotropy, induced currents mainly flow within the a-b plane. When the c-axis is not parallel to the external field, a large torque acts on the BHTSC so as to align the c-axis of the specimen parallel to the direction of external field. The BHTSC often tilts with such torque force that an extra support is necessary to withstand the torque. 9 EN 61788-9:2005 A large electromagnetic force act
