SIST EN IEC 61788-24:2018

SLOVENSKI STANDARD
SIST EN IEC 61788-24:2018
01-november-2018
6XSHUSUHYRGQRVWGHO0HULWYHNULWLþQHJDWRND2EGUåDQLNULWLþQLWRNSR
GYRMQHPXSRJLEXSRVUHEUHQLK%LVXSHUSUHYRGQLKåLFSULVREQLWHPSHUDWXUL
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Superconductivity - Part 24: Critical current measurement - Retained critical current after
double bending at room temperature of Ag-sheathed Bi-2223 superconducting wires
(IEC 61788-24:2018)
Supraleitfähigkeit - Teil 24: Messung des kritischen Stroms - Verbleibender kritischer
Strom nach Doppelbiegung bei Raumtemperatur in Ag-ummantelten Bi-2223
supraleitenden Drähten
Supraconductivité - Partie 24: Mesurage du courant critique - Courant critique retenu
après double flexion à température ambiante des fils supraconducteurs Bi-2223 avec
gaine Ag
Ta slovenski standard je istoveten z: EN IEC 61788-24:2018
ICS:
17.220.20 0HUMHQMHHOHNWULþQLKLQ Measurement of electrical
PDJQHWQLKYHOLþLQ and magnetic quantities
29.050 Superprevodnost in prevodni Superconductivity and
materiali conducting materials
29.060.10 Žice Wires
SIST EN IEC 61788-24:2018 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN IEC 61788-24:2018

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SIST EN IEC 61788-24:2018


EUROPEAN STANDARD EN IEC 61788-24

NORME EUROPÉENNE

EUROPÄISCHE NORM
August 2018
ICS 29.050; 77.040.10; 17.220

English Version
Superconductivity - Part 24: Critical current measurement -
Retained critical current after double bending at room
temperature of Ag-sheathed Bi-2223 superconducting wires
(IEC 61788-24:2018)
Supraconductivité - Partie 24: Mesurage du courant critique Supraleitfähigkeit - Teil 24: Messung des kritischen Stroms
- Courant critique retenu après double flexion à température - Verbleibender kritischer Strom nach Doppelbiegung bei
ambiante des fils supraconducteurs Bi-2223 avec gaine Ag Raumtemperatur in Ag-ummantelten Bi-2223
(IEC 61788-24:2018) supraleitenden Drähten
(IEC 61788-24:2018)
This European Standard was approved by CENELEC on 2018-07-23. 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 national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application 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 other language made by translation
under the responsibility of a CENELEC member into its own language and notified to 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, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden,
Switzerland, Turkey and the United Kingdom.


European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2018 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
 Ref. No. EN IEC 61788-24:2018 E

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SIST EN IEC 61788-24:2018
EN IEC 61788-24:2018 (E)
European foreword
The text of document 90/402/FDIS, future edition 1 of IEC 61788-24, prepared by IEC/TC 90
"Superconductivity" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as
EN IEC 61788-24:2018.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2019-04-23
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2021-07-23
document have to be withdrawn


Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.

Endorsement notice
The text of the International Standard IEC 61788-24:2018 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following note has to be added for the standard indicated:
IEC 61788-3 NOTE Harmonized as EN 61788-3


2

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SIST EN IEC 61788-24:2018
EN IEC 61788-24:2018 (E)
Annex ZA
(normative)

Normative references to international publications
with their corresponding European publications
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
NOTE 1  Where an International Publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
NOTE 2  Up-to-date information on the latest versions of the European Standards listed in this annex is available here:
www.cenelec.eu.
Publication Year Title EN/HD Year
IEC 60050-815 2015 International Electrotechnical Vocabulary - - -
Part 815: Superconductivity




3

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SIST EN IEC 61788-24:2018




IEC 61788-24

®


Edition 1.0 2018-06




INTERNATIONAL



STANDARD




NORME



INTERNATIONALE
colour

inside










Superconductivity –

Part 24: Critical current measurement – Retained critical current after double

bending at room temperature of Ag-sheathed Bi-2223 superconducting wires




Supraconductivité –

Partie 24: Mesurage du courant critique – Courant critique retenu après double


flexion à température ambiante des fils supraconducteurs Bi-2223 avec gaine Ag













INTERNATIONAL

ELECTROTECHNICAL

COMMISSION


COMMISSION

ELECTROTECHNIQUE


INTERNATIONALE




ICS 17.220; 29.050; 77.040.10 ISBN 978-2-8322-5801-9




Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

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SIST EN IEC 61788-24:2018
– 2 – IEC 61788-24:2018 © IEC 2018
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Principle . 8
5 Apparatus . 8
5.1 General . 8
5.2 Bending mandrel . 8
5.3 Critical current measurement holder . 8
5.4 Critical current measuring system . 9
6 Specimen preparation and set up . 9
6.1 Length of specimen . 9
6.2 Mounting of the specimen . 10
7 Measurement procedures . 10
7.1 Critical current measurement . 10
7.2 Double bending . 10
7.3 Retained critical current after bending . 11
8 Calculation of results . 11
8.1 Critical current criteria. 11
8.2 n-value (optional) . 11
9 Test report . 11
9.1 Identification of test specimen . 11
9.2 Report of I values and/or retained I ratio . 12
c c
9.3 Report of I test conditions . 12
c
Annex A (informative) Additional information relating to Clauses 1 to 9 . 13
A.1 General . 13
A.2 Measurement condition . 13
A.3 Apparatus measurement holder material . 13
A.4 Specimen preparation . 16
A.5 Measurement procedures . 16
A.5.1 Critical current measurement . 16
A.5.2 Bending . 18
A.6 Calculation of results . 19
A.6.1 Critical current criteria . 19
A.6.2 n-value . 19
A.7 Relative standard uncertainty . 20
Annex B (informative) Evaluation of combined standard uncertainty for the retained I
c
after double bending . 22
B.1 Practice of critical current measurement . 22
B.2 Model equation . 22
B.3 Operation for the retained I measurement . 23
c
B.4 Combined standard uncertainty . 23

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IEC 61788-24:2018 © IEC 2018 – 3 –
B.5 Evaluation of standard uncertainty (SU) for each measurand . 24
B.5.1 Voltage tap length (L) . 24
B.5.2 Voltage (U) . 24
B.5.3 Current (I) . 25
B.6 Evaluation of combined standard uncertainty . 26
Bibliography . 29

Figure 1 – Sample holder . 9
Figure 2 – Intrinsic U-I characteristic . 12
Figure 3 – U-I characteristic with a current transfer component . 12
Figure A.1 – Measurement configuration for a few hundred ampere class conductor . 15
Figure A.2 – Clips . 15
Figure A.3 – Additional strain caused by voltage tap wires and solders . 16
Figure A.4 – Boiling temperature of liquid nitrogen versus atmospheric pressure . 17
Figure A.5 – Critical current versus temperature for a typical Bi-2223 wire . 18
Figure A.6 – Bending process . 19
Figure B.1 – U-I diagram . 22
Figure B.2 – Bending diameter dependence of the retained I and , where the
c COV
calculated curve of I /I gives Equation (B.24). 28
c c0

Table A.1 – Thermal expansion data of Bi-2223 superconductors and selected
materials . 14
Table A.2 – Average of the degree of retained critical current (I /I ), their relative
c c0
standard uncertainty and coefficient of variance. 21
Table B.1 – Precondition for evaluating standard uncertainty . 22
Table B.2 – Partial sum (Equation (B.17) of standard uncertainty as related to the
current measurement) . 26
Table B.3 – Budget table of standard uncertainty for each component . 27
Table B.4 – Combined standard uncertainty . 27

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SIST EN IEC 61788-24:2018
– 4 – IEC 61788-24:2018 © IEC 2018
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

SUPERCONDUCTIVITY –

Part 24: Critical current measurement –
Retained critical current after double bending at room
temperature of Ag-sheathed Bi-2223 superconducting wires

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
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agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61788-24 has been prepared by IEC technical committee 90:
Superconductivity:
The text of this standard is based on the following documents:
FDIS Report on voting
90/402/FDIS 90/406/RVD

Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

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SIST EN IEC 61788-24:2018
IEC 61788-24:2018 © IEC 2018 – 5 –
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.

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SIST EN IEC 61788-24:2018
– 6 – IEC 61788-24:2018 © IEC 2018
INTRODUCTION
In 1988, a new class of high critical temperature (T ) copper oxide superconductors,
c
Bi-Sr-Ca-Cu-O, was discovered. After nearly three decades, (Bi,Pb) Sr Ca Cu O (Bi-2223)
2 2 2 3 x
is now being utilized as a commercial high-T superconducting wire.
c
Superconducting wires are often subjected to bending deformation during production and
application, e.g. during wire processing, magnet construction, cable fabrication, etc. The wire
is bent towards both the upper and lower directions as it passes through several pulleys.
These production processes are carried out at room temperature. Critical current of the wire is
likely influenced through such bending, and may be accompanied by irreversible degradation
in case of large deformation. The easiest way to evaluate the influence of bending on critical
current is to carry out comparative measurement with the wire in the straight form before and
after bending to a specific diameter.
After a wire is made into a coil or a cable, critical current is often measured under bending
conditions or a more complex deformation state. In these cases, change in critical current
may include both reversible and irreversible contributions depending on the amount of
deformation. Irreversible degradation usually originates from a fracture in the superconducting
component. In order to evaluate only irreversible contributions, measuring the retained critical
current after the wire is straightened back from its deformed shape is necessary.
The critical bending diameter below which wire performance degrades significantly is typically
specified for use of commercial superconducting wire. Thus, it is important to standardize
measurement methods for the retained critical current after double bending. This document
can be applied to other similar bending tests such as single bending, cyclic bending, etc.
This document consists of two fundamental technologies of the critical current measurement
and the double bending process.

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SIST EN IEC 61788-24:2018
IEC 61788-24:2018 © IEC 2018 – 7 –
SUPERCONDUCTIVITY –

Part 24: Critical current measurement –
Retained critical current after double bending at room
temperature of Ag-sheathed Bi-2223 superconducting wires



1 Scope
This part of IEC 61788 describes a test method for determining the retained critical current
after double bending at room temperature of short and straight Ag- and/or Ag alloy-sheathed
Bi-2223 superconducting wires that have the shape of a flat or square tape containing mono-
or multicores of oxides. The wires can be laminated with copper alloy, stainless steel or Ni
alloy tapes.
The test method is intended for use with superconductors that have a critical current less than
300 A and an n-value larger than 5. The test to determine the retained critical current is
carried out without an applied magnetic field, with the test specimen immersed in a liquid
nitrogen open bath.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements 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 60050-815:2015, International Electrotechnical Vocabulary – Part 815: Superconductivity
(available at http://www.electropedia.org/)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-815 and the
following apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
double bending
bending in one direction to a certain diameter followed by the subsequent bending in the
opposite direction to the same diameter
Note 1 to entry: Bending diameter is defined as the diameter of the bending mandrel.
Note 2 to entry: The definition of bending diameter is in principle the sum of the mandrel diameter and
superconductor thickness. In the engineering process, however, the minimum diameter of the pulleys through
which the wire is passed should also be considered.

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3.2
constant sweep rate method
voltage-current data (U-I data) acquisition method where a current is swept at a constant rate
from zero to a value above critical current (I ) while continuously or frequently and
c
periodically acquiring U-I data
3.3
ramp-and-hold method
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 of these points while
acquiring a number of voltages and current readings
4 Principle
The principle of the double bending method is described as follows. Critical current at 77 K
under self-field shall be measured in a straight configuration with no mechanical strain. After
measurement the specimen shall be warmed up to room temperature.
Hereafter, the specimen shall be bent in one direction to the specified diameter and then
returned to the straight configuration. Successively, the specimen shall be bent in the
opposite direction to the same diameter and returned to the straight configuration again.
Critical current of the specimen at 77 K under self-field shall be measured after double
bending and straightening. The time interval between critical current measurements before
and after bending should be as short as possible.
Critical current is determined from voltage-current (U-I) characteristic measured in a liquid
nitrogen open bath under a constant pressure. Critical current is determined as the current at
a specific electric field strength criterion (electric field criterion) (E ), which corresponds to the
c
voltage criterion (U ) for a specified voltage tap separation.
c
5 Apparatus
5.1 General
The apparatuses required for the present test methods include the following:
• mandrels with necessary bending diameters;
• critical current measuring system.
5.2 Bending mandrel
Bending diameter shall be defined as the diameter of the bending mandrel. Bendable length
shall be longer than the distance between the voltage taps.
5.3 Critical current measurement holder
The measurement holder is constructed from an insulating material.
Critical current may inevitably depend on the measurement holder material due to specimen
strain induced by the difference of thermal contraction between specimen and holder.
The structure of the measurement holder shall be one which does not induce a local excess
strain. The specimen strain induced by the difference of thermal contraction between
specimen and holder during cooling from room temperature to 77 K shall be minimized to
within ± 0,1 %. This thermal strain can be evaluated in cases where the thermal expansion

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SIST EN IEC 61788-24:2018
IEC 61788-24:2018 © IEC 2018 – 9 –
coefficients of constituent materials are known. To minimize the thermal strain, the holder
shall be constructed from material which has a thermal contraction similar to the specimen.
NOTE Recommended measurement holder materials are described in A.3.
5.4 Critical current measuring system
The apparatus to measure U-I characteristics consists of a specimen probe, an open bath of
liquid nitrogen and a U-I measurement system.
The specimen probe, which consists of a specimen, a measurement holder and a specimen
support structure, is inserted in the open bath filled with liquid nitrogen. The U-I measurement
system consists of a direct current source, a recorder and necessary preamplifiers, filters or
voltmeters, or a combination thereof.
A computer-assisted data acquisition system is recommended.
6 Specimen preparation and set up
6.1 Length of specimen

The length (L) of the specimen to be measured shall be determined as follows (see Figure 1):
L = 2 × L + 2 × L + L + 2 × L > 5 × W (1)
2 4 1 3
L ≥ W, L ≥ W, L ≥ W (2)
1 2 3
where
L is the distance between the voltage taps;
1
L is the length of the current contact;
2
L is the shortest distance from the current contact to the voltage tap;
3
L is the width of the voltage tap;
4
W is the width of the specimen to be measured.
L L L L L L L
2 3 4 1 4 3 2

Current
Current Voltage
Voltage
IEC

Figure 1 – Sample holder
For a specimen with a larger current-carrying capacity/width, L shall be longer than 3W. In
2
cases where the specimen is laminated with stainless steel or laminated with another highly
resistive material, L shall be larger. For measurement which requires higher voltage
2
sensitivity, L shall be larger. In cases where current transfer voltage cannot be ignored, L shall
1 3
be larger.

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1
In Table 2 of [1] , five successful double bend test conditions are shown. Typically, specimen
length L ranges from 90 mm to 150 mm, L from 18,25 mm to 50 mm, L from 10 mm to
1 2
20 mm, L from 12,5 mm to 20 mm, and
...