SIST EN ISO 17279-3:2021

SLOVENSKI STANDARD
01-maj-2021
Varjenje - Mikro spajanje visokotemperaturnih superprevodnikov druge generacije
- 3. del: Preskusne metode za zvarne spoje (ISO 17279-3:2021)
Welding - Micro joining of second generation high temperature superconductors - Part 3:
Test methods for joints (ISO 17279-3:2021)
Schweißen - Mikrofügen von Hochtemperatursupraleitern der 2. Generation - Teil 3:
Prüfverfahren von Fügeverbindungen (ISO 17279-3:2021)
Soudage - Micro-assemblage des supraconducteurs à haute température de deuxième
génération - Partie 3: Méthode d'essai des assemblages (ISO 17279-3:2021)
Ta slovenski standard je istoveten z: EN ISO 17279-3:2021
ICS:
25.160.40 Varjeni spoji in vari Welded joints and welds
29.050 Superprevodnost in prevodni Superconductivity and
materiali conducting materials
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 17279-3
EUROPEAN STANDARD
NORME EUROPÉENNE
March 2021
EUROPÄISCHE NORM
ICS 25.160.01
English Version
Welding - Micro joining of second generation high
temperature superconductors - Part 3: Test methods for
joints (ISO 17279-3:2021)
Soudage - Micro-assemblage des supraconducteurs à Schweißen - Mikrofügen von
haute température de deuxième génération - Partie 3: Hochtemperatursupraleitern der 2. Generation - Teil 3:
Méthode d'essai des assemblages (ISO 17279-3:2021) Prüfverfahren von Fügeverbindungen (ISO 17279-
3:2021)
This European Standard was approved by CEN on 4 March 2021.

CEN 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 CEN
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 CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 17279-3:2021 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 17279-3:2021) has been prepared by Technical Committee ISO/TC 44 "Welding
and allied processes" in collaboration with Technical Committee CEN/TC 121 “Welding and allied
processes” the secretariat of which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by September 2021, and conflicting national standards
shall be withdrawn at the latest by September 2021.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 17279-3:2021 has been approved by CEN as EN ISO 17279-3:2021 without any
modification.
INTERNATIONAL ISO
STANDARD 17279-3
First edition
2021-02
Welding — Micro joining of second
generation high temperature
superconductors —
Part 3:
Test methods for joints
Soudage — Micro-assemblage des supraconducteurs à haute
température de deuxième génération —
Partie 3: Méthode d'essai des assemblages
Reference number
ISO 17279-3:2021(E)
©
ISO 2021
ISO 17279-3:2021(E)
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
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Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved

ISO 17279-3:2021(E)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Test methods for joint . 1
4.1 General . 1
4.2 Visual testing . 2
4.2.1 General. 2
4.2.2 Qualification of test personnel . 2
4.2.3 Test equipment . 2
4.2.4 Surface condition and preparation . 2
4.2.5 Testing . 2
4.2.6 Acceptance criteria . 2
4.2.7 Test report . 3
4.3 Four-point-probe testing . 3
4.3.1 General. 3
4.3.2 Qualification of test personnel . 3
4.3.3 Test equipment . 3
4.3.4 Surface condition and preparation . 3
4.3.5 Testing . 3
4.3.6 Acceptance criteria . 9
4.3.7 Test report . 9
4.4 Field-decay testing . 9
4.4.1 General. 9
4.4.2 Qualification of test personnel . 9
4.4.3 Test equipment . 9
4.4.4 Surface condition and preparation . 9
4.4.5 Testing . 9
4.4.6 Acceptance criteria .12
4.4.7 Test teport.12
4.5 In-field testing .12
4.5.1 General.12
4.5.2 Qualification of test personnel .12
4.5.3 Test equipment .12
4.5.4 Surface condition and preparation .12
4.5.5 Testing .12
4.5.6 Acceptance criteria .15
4.5.7 Test report .15
4.6 Tensile testing .15
4.6.1 General.15
4.6.2 Qualification of test personnel .15
4.6.3 Test equipment .15
4.6.4 Surface condition and preparation .15
4.6.5 Testing .15
4.6.6 Acceptance criteria .16
4.6.7 Test report .16
4.7 Bend testing .16
4.7.1 General.16
4.7.2 Qualification of test personnel .16
4.7.3 Test equipment .16
4.7.4 Surface condition and preparation .16
4.7.5 Testing .16
ISO 17279-3:2021(E)
4.7.6 Acceptance criteria .17
4.7.7 Test report .17
4.8 Critical magnetic field testing .17
4.8.1 General.17
4.8.2 Qualification of test personnel .17
4.8.3 Test equipment .17
4.8.4 Surface condition and preparation .17
4.8.5 Testing .18
4.8.6 Acceptance criteria .18
4.8.7 Test report .18
4.9 Critical current density distribution testing .18
4.9.1 General.18
4.9.2 Qualification of test personnel .18
4.9.3 Test equipment .19
4.9.4 Surface condition and preparation .19
4.9.5 Testing .19
4.9.6 Acceptance criteria .19
4.9.7 Test report .19
4.10 Microscopic and X-ray diffraction testing .19
4.10.1 General.19
4.10.2 Qualification of test personnel .19
4.10.3 Test equipment .19
4.10.4 Surface condition and preparation .19
4.10.5 Testing .20
4.10.6 Acceptance criteria .20
4.10.7 Reporting .20
Annex A (informative) Report of visual testing results .21
Annex B (informative) Report of four-point-probe testing results .23
Annex C (informative) Report of field-decay testing results .26
Annex D (informative) Report of in-field testing results .29
Annex E (informative) Report of tensile testing results .33
Annex F (informative) Report of bend testing results .36
Annex G (informative) Report of critical magnetic field testing results .39
Annex H (informative) Report of critical current density distribution testing results .41
Annex I (informative) Report of microscopic and X-ray diffraction testing results .43
Bibliography .45
iv © ISO 2021 – All rights reserved

ISO 17279-3:2021(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 44, Welding and allied processes,
Subcommittee SC 10, Quality management in the field of welding, in collaboration with the European
Committee for Standardization (CEN) Technical Committee CEN/TC 121, Welding and allied processes,
in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
A list of all parts in the ISO 17279 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
Official interpretations of ISO/TC 44 documents, where they exist, are available from this page: https://
committee .iso .org/ sites/ tc44/ home/ interpretation .html.
ISO 17279-3:2021(E)
Introduction
The increasing use of second-generation high temperature superconductors (2G HTSs) and invention
of resistance-free joining on 2G HTSs have created the need for the ISO 17279 series in order to ensure
that joining is carried out in the most effective way and that appropriate control is exercised over all
aspects of the operation. ISO standards for micro-joining and joint evaluation procedure are accordingly
essential to get the best and uniform quality of 2G HTS joint.
Superconductor is a material that conducts electricity without resistance and has diamagnetism below
critical temperature (T ), critical magnetic field (B ) and critical current density (J ). Once set in motion,
c c c
electrical current flows forever in a closed loop of superconducting material under diamagnetism.
2G HTS constitutes of multi-layers and total thickness is around 60 μm to 90 μm and the superconducting
layer made from REBa Cu O is only 1 μm to 3 μm thick depending on manufacturer’s specifications.
2 3 7-x
Figure 1 shows schematic drawing of typical multiple layers, and the constituents and thicknesses of
each layer in the 2G HTS.
Dimensions in micro-meters
Key
1 Cu stabilizer t thickness of layer 1
2 Ag overlayer t thickness of layer 2
3 REBCO-superconducting layer t thickness of layer 3
4 buffer stack t thickness of layer 4
5 hastelloy®C-276 substrate t thickness of layer 5
NOTE Not to scale.
Figure 1 — Typical 2G HTS multi-layers, and the constituents and thicknesses of each layer
vi © ISO 2021 – All rights reserved

ISO 17279-3:2021(E)
Currently soldering, brazing or any filler is applying in superconducting industry as shown in Figure 2,
which shows high electrical resistance at the joint providing fatal flaw in the superconductor.
a)  Lap joint b)  Bridge joint
Key
1 REBCO-superconducting layer
2 solder
Figure 2 — Soldering to join 2G HTS
However, the ISO 17279 series focuses on the direct autogenous joining of 1 μm to 3 μm thick
superconducting layers of 2G HTSs as shown in Figure 3 without filler metals and recovery of
superconducting properties by oxygenation annealing process, which shows almost none electrical
resistance at the joint.
a)  Lap joint b)  Bridge joint
Key
1 REBCO-superconducting layer
Figure 3 — Direct autogenous joining of 1 μm to 3 μm thick superconducting layers of 2G HTSs
for superconducting joint
ISO 17279-1 specifies requirements for the qualification of 2G HTS joining procedure. 2G HTS joints
should be capable of performing required electric, magnetic and mechanical properties and free from
serious imperfections in production and in service. To achieve that goal, it is necessary to provide
controls during design and fabrication.
ISO 17279-2 specifies requirements for the qualification of personnel performing welding and testing.
INTERNATIONAL STANDARD ISO 17279-3:2021(E)
Welding — Micro joining of second generation high
temperature superconductors —
Part 3:
Test methods for joints
1 Scope
This document specifies the requirements for the test methods for joint of micro-joining of 2G HTS to
fulfil the requirements of ISO 17279-1 and ISO 17279-2.
This document specifies test methods for determining the capability of joints for the production of the
specified quality. It defines specific test requirements, but does not assign those requirements to any
specific product group.
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.
ISO 17279-1:2018, Welding — Micro joining of 2nd generation high temperature superconductors — Part 1:
General requirements for the procedure
ISO 15607:2019, Specification and qualification of welding procedures for metallic materials — General rules
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 17279-1 and ISO 15607 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Test methods for joint
4.1 General
ISO 17279-1:2018, 5.5.4, describes requirements for qualification of test personnel, for test methods,
witness during testing and retesting. Especially, ISO 17279-1:2018, Table 1, shows the type of testing,
the extent of testing, the confirmation of testing, and required tests for the procedure qualification
according to ISO 17279-1. ISO 17279-1:2018, 5.9, requires the acceptance criteria of the tests. The
manufacturer can have at their disposal sufficient competent personnel for the testing and operating
the test equipment, or can contract the specific tests to the specialized organizations. The manufacturer
can witness the tests from specimen preparation to data acquisition and analysis according to
manufacturer’s quality assurance requirements.
The operating procedures and cautions of the test equipment shall be applied when the equipment is
used for testing according to this document. The operator of the specific equipment shall establish the
capability to perform the required test, and calibration and qualification of the test equipment shall
ISO 17279-3:2021(E)
be maintained up-to-date according to an appropriate quality management program. Qualification
records and certificates shall be kept up-to-date.
The tests except visual testing shall be performed at the cryogenic environment and do not purport to
address the safety concerns associated with its use. It is the responsibility of whoever uses this method
to establish appropriate safety and health practices prior to use.
4.2 Visual testing
4.2.1 General
This subclause defines the method of visual testing of materials and joints used in 2G HTS.
4.2.2 Qualification of test personnel
Testing shall be conducted by qualified personnel. Personnel qualification shall be done according to
an appropriate quality management program. Personnel conducting visual testing shall annually pass
an examination where their vision, with or without correction, meets the Jaeger J2 near vision test at a
distance not less than 30,5 cm as well as a colour perception test. The vision examination records shall
be maintained for the current year and shall be available for review.
4.2.3 Test equipment
Calibrated instruments shall be used for testing, wherever required, this includes all necessary
measuring instruments and gauges.
4.2.4 Surface condition and preparation
The surface for the test shall be uniform and smooth and shall be clean and free of scale, rust, oil,
grease, detrimental oxides and other deleterious foreign materials such as Ag or Cu spots of 2G HTS.
The surfaces of the finished joints shall be suitable to permit proper testing. All joint preparations
shall meet drawing specified dimensions (whether provided via dimensions on the drawing or in a
welding specification). If no dimensions are provided as part of the drawing or ordering documents, the
dimensions shall meet dimensions specified by approved welding procedure specification (WPS).
4.2.5 Testing
Testing shall be performed in accordance with a written procedure or method applicable under testing.
The testing area shall include the joint and the accessible adjacent heat-affected zone (HAZ) for some
distance from the joint edge of the base metal. The testing shall be in the after joining and final heat-
treated condition (oxygenation annealing), or otherwise required, and be free of all coatings and other
surface conditions such as paint, plating, etc. The joints shall be tested in the as-welded condition.
Testing will be conducted with specimen suitable dimensions.
Direct visual testing shall be used. If required, mirrors and magnifying lenses are used to improve the
angle of vision and to assist. The minimum light intensity at the surface is 1 000 lux (100 foot-candles).
The written procedure or method shall include, at a minimum and either directly or by reference to
applicable document(s), procedure identification number and date, revision number, identification of
joints, complete testing requirements including lighting and method of testing, evaluation of indications,
acceptance criteria, disposition of joints after evaluations.
4.2.6 Acceptance criteria
The requirements of ISO 17279-1:2018, Table 4, shall be met. Lack of bonding, lack of fusion, cracks and
pin holes are not acceptable.
2 © ISO 2021 – All rights reserved

ISO 17279-3:2021(E)
4.2.7 Test report
After the completion of the testing, the results shall be entered in the test report. A form of a test report
is shown in Annex A.
4.3 Four-point-probe testing
4.3.1 General
This subclause defines the method of four-point-probe testing of base materials and joints used in
2G HTS. Critical current (I ), critical current density (J ) and n-value can be measured from the test.
c c
NOTE Typically, the resistance of the point of contact (contact resistance) is far smaller than the resistance
of the test specimen, and can thus be ignored. However, for superconductors under cryogenic conditions, the
contact resistance can dominate and completely obscure changes in the resistance of the test specimen itself.
The effects of contact resistance are eliminated with the use of four-point-probe testing.
4.3.2 Qualification of test personnel
Testing shall be conducted by qualified personnel. Personnel qualification shall be done according to an
appropriate quality management program.
4.3.3 Test equipment
Calibrated instruments shall be used for testing.
4.3.4 Surface condition and preparation
Subclause 4.2.4 shall apply.
4.3.5 Testing
4.3.5.1 General
Testing shall be performed in accordance with a written test procedure or method applicable to the
2G HTS. The written test procedure or method shall include, at a minimum and either directly or
by reference to applicable document(s), procedure identification number, date, revision number,
identification of joints, complete testing requirements including method of testing, evaluation and
reporting after evaluations.
The testing area shall include the joint and the accessible adjacent HAZ of base material for some
distance from the joint edge. The total length of specimen shall be at least 60 mm including 20 mm
joint. The test shall be done after joining and final heat-treated condition (oxygenation annealing),
or otherwise required, and is carried out at the LN2 cryogenic environment or other temperature
determined by the manufacturer. The test shall be done at weld reinforced condition with commercially
available materials considering thermal shrinkage coefficient so as not for joints to be damaged during
the test.
Schematic of two superconducting layers with lap-joint in 2G HTS is shown in Figure 4. When current
passes through a superconducting layer (1 μm to 3 μm thick) of 2G HTS from superconducting layer 1 to
joint to superconducting layer 2, the current generates a voltage difference between superconducting
layer 1 and superconducting layer 2. 2G HTS without joint and HAZ is resistance-free in cryogenic
environment, thus the most voltage difference comes from joint and HAZ.
ISO 17279-3:2021(E)
Dimensions in micro-meters
Key
1 upper superconducting layer
2 bottom superconducting layer
3 joining area
w width of superconducting layer
t thickness of superconducting layer (1 μm~3 μm)
t almost 2 t or slightly less than 2 t depending on pressure during joining
2 1 1
A cross-sectional area of superconducting layers 1 and 2 (A = t × w)
1 1 1
A cross-sectional area of lap-joined two superconducting layers (A = t × w)
2 2 2
Figure 4 — Typical 2G HTS multi-layers, and the constituents and thicknesses of each layer
Figure 5 is a schematic of four-point-probe testing in lap-joined 2G HTS. Four probes are attached to the
test specimen as shown in the figure. A current is made to flow the length of the test specimen through
probes labelled a and b in the Figure 5. This can be done using a current source or a power supply
having current output readout. If the test specimen has any resistance to the flow of electrical current,
then there is a drop of potential (or voltage) as the current flows along the test specimen, for example
between the two probes labelled c and d in the figure. The voltage drop between probes c and d can be
measured by a digital voltmeter. The resistance of the test specimen between probes c and d is the ratio
of the voltage registering on the digital voltmeter to the value of the output current of the power supply.
The high impedance of the digital voltmeter minimizes the current flow through the portion of the
circuit comprising the voltmeter. Thus, since there is no potential drop across the contact resistance
associated with probes c and d, only the resistance associated with the joint and associated HAZ of
superconductor between probes c and d is measured as a function of current. 2 HAZ lengths adjacent
to the joint are about twice of joint length. However, the HAZ is dependent on the heat input and dwell
time during joining. Manufacturer may determine the HAZ length by four-point-probe testing.
4 © ISO 2021 – All rights reserved

ISO 17279-3:2021(E)
Key
1 joining area
2 heat-affected zone (HAZ)
R electrical resistance of the joint
j
a
Current lead 1.
b
Current lead 2.
c
Voltage tap 1.
d
Voltage tap 2.
Figure 5 — Schematic of four-point-probe testing in lap-joined 2G HTS CC
The test procedure is as follows.
a) Attach c and d (joint fusion line each) probes to the test specimen and connect to a digital voltmeter
and attach a and b (5 mm from the c and d each) probes to an ammeter and a power supply. A strip
chart recorder may be connected between probes c and d.
b) Set the thermocouple reader to read the K thermocouple and read the symbol of the thermocouple
attached to the thermocouple. Do not bend the thermocouple.
c) Place the container, test specimen with attached probes, and thermocouple. Pour liquid nitrogen or
other cryogen into the container. Read the potential across the thermocouple.
d) When the container is completely cooled and the temperature drops to about 70 K or whatever
decided, turn the power supply on. When the resistance of the superconductor changes with
variable current, the voltage output changes. Read the potential difference on the voltmeter.
The ratio of the voltage to the current flowing through the test specimen is the resistance of the
superconductor between the two voltage probes (c and d).
In Figure 5, current (I) passes through the two end probes (a and b) and voltage (V) is measured
between the two centre probes (c and d) which is for joint and HAZ. The average resistance, R, between
the two centre probes (c and d) is calculated from Formula (1).
I = V / R (1)
where
V is the voltage difference;
I is the current flow between the two centre probes (c and d).
ISO 17279-3:2021(E)
R is also given by Formula (2) because most voltage difference comes from joint and HAZ.
R = ρ × l / A or R = ρ × l / A (2)
j j j 2 HAZ HAZ HAZ 1
where is
ρ is the resistivity of the joint in Ω-cm;
j
ρ is the resistivity of the HAZ in Ω-cm;
HAZ
l is the length of the joint measured in cm;
j
l is the length of the HAZ measured in cm;
HAZ
A and A is the cross-sectional areas of superconducting layer and lap-joined two superconduct-
1 2
ing layers in cm , respectively.
Thus, total resistance of the test specimen with lap-joint is as Formula (3).
I = V / (R + R) (3)
j HAZ
4.3.5.2 Self-field critical current (I )
c
Critical current value of joint (I ) is extremely important to confirm joint integrity. The self-field
c,j
critical current (I ) values of the joined superconductor shall be measured using a standard four-point-
c
probe testing and in a bath of liquid nitrogen (LN ) or other pre-determined cryogenic environment.
Although this method is not an ultimate method, it is quite effective in the first-round evaluation. If the
current is plotted versus the voltage reading in 2G HTS, the result is similar to that shown in Figure 6.
1)
The V-I curve is obtained from a commercially available data acquisition system (DAS) and LabVIEW .
The DAS and LabVIEW shall be calibrated.
1) LabVIEW is the trademark of a product. This information is given for the convenience of users of this document
and does not constitute an endorsement by ISO of the product named. Equivalent products may be used if they can
be shown to lead to the same results.
6 © ISO 2021 – All rights reserved

ISO 17279-3:2021(E)
Key
X current in A
Y voltage in V
Figure 6 — Examples of V-I curve measured in joint of 2G HTS CC
Figure 6 a) and b) show resistance and are not superconducting joints. However, Figure 6 c) and d) shows
perfect superconducting joint, of which the slope of V−I curve is zero (zero voltage and resistance) till
around its critical current (I ). Figure 6 c) is lower than the virgin (heat-unaffected base metal) and
c
Figure 6 d) is same of the virgin, respectively. The self-field I values of the 2G HTS joint shall be measured
c
using a 1 μV/cm criterion from the V-I curve obtained by four-point-probe testing. When the distance
between voltage taps [Figure 6 c) and d)] is 8 cm, the current value at 8 μV is critical current (I ).
c
4.3.5.3 Critical current density (J )
C
J characterizes the maximum electrical transport current per cross-sectional unit area that the
c
superconductor is able to maintain without resistance and is expressed in terms of I divided by joined
c
cross-sectional area. The cross-sectional areas of virgin (base metal) and joint in Figure 4 are A and A
1 2
respectively and expressed as Formula (4).
J = I / A or J = I / A (4)
c,v c,v 1 c,j c,j 2
For example, when the thickness and width of superconducting layer in 2G HTS are 1 μm and 4 μm,
2 2
respectively, and I of 84 A in Figure 6 d) is applied, A and A are 4 μm and 8 μm . Then, J and J can
c 1 2 c,v c,j
2 2
be calculate
...