EN 61788-8:2003

SLOVENSKI SIST EN 61788-8:2003

STANDARD
oktober 2003
Superconductivity - Part 8: AC loss measurements - Total AC loss measurement of
Cu/Nb-Ti composite superconducting wires exposed to a transverse alternating
magnetic field by a pickup coil method
ICS 17.220.20; 29.050 Referenčna številka
©  Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno

EUROPEAN STANDARD EN 61788-8
NORME EUROPÉENNE
EUROPÄISCHE NORM May 2003
ICS 17.220; 29.050
English version
Superconductivity
Part 8: AC loss measurements -
Total AC loss measurement of Cu/Nb-Ti composite superconducting wires
exposed to a transverse alternating magnetic field
by a pickup coil method
(IEC 61788-8:2003)
Supraconductivité Supraleitfähigkeit
Partie 8: Mesure des pertes Teil 8: Messung der
en courant alternatif - Wechselstromverluste -
Méthode de mesure par bobines Messung der gesamten
de détection des pertes totales Wechselstromverluste von
en courant alternatif des fils composites Cu/NbTi-Verbundsupraleiterdrähten
supraconducteurs de Cu/Nb-Ti in transversalen magnetischen
exposés à un champ magnétique Wechselfeldern mit Hilfe eines
alternatif transverse Pickupspulen-Verfahrens
(CEI 61788-8:2003) (IEC 61788-8:2003)

This European Standard was approved by CENELEC on 2003-05-01. 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 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 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 Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Czech Republic,
Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta,
Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels

© 2003 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 61788-8:2003 E
Foreword
The text of document 90/135A/FDIS, future edition 1 of IEC 61788-8, prepared by IEC TC 90,
Superconductivity, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC
as EN 61788-8 on 2003-05-01.
The following dates were fixed:

– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement dop) 2004-02-01

– latest date by which the national standards conflicting
with the EN have to be withdrawn dow) 2006-05-01

Annexes designated "normative" are part of the body of the standard.
Annexes designated "informative" are given for information only.
In this standard, annex ZA is normative and annexes A to E are informative.
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 61788-8:2003 was approved by CENELEC as a European
Standard without any modification.
__________
- 3 - «Field32»
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
This European Standard incorporates by dated or undated reference, provisions from other
publications. These normative references are cited at the appropriate places in the text and the
publications are listed hereafter. For dated references, subsequent amendments to or revisions of any
of these publications apply to this European Standard only when incorporated in it by amendment or
revision. For undated references the latest edition of the publication referred to applies (including
amendments).
NOTE When an international publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
Publication Year Title EN/HD Year
1)
IEC 60050-815 - International Electrotechnical - -
Vocabulary (IEV)
Chapter 815: Superconductivity

1)
Undated reference.
NORME CEI
INTERNATIONALE IEC
61788-8
INTERNATIONAL
Première édition
STANDARD
First edition
2003-04
Supraconductivité –
Partie 8:
Mesure des pertes en courant alternatif –
Méthode de mesure par bobines de détection
des pertes totales en courant alternatif des fils
composites supraconducteurs de Cu/Nb-Ti
exposés à un champ magnétique alternatif
transverse
Superconductivity –
Part 8:
AC loss measurements –
Total AC loss measurement of Cu/Nb-Ti composite
superconducting wires exposed to a transverse
alternating magnetic field by a pickup coil method
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For price, see current catalogue

61788-8 © IEC:2003 – 3 –
CONTENTS
FOREWORD . 5
INTRODUCTION .7
1 Scope . 9
2 Normative references. 9
3 Terms and definitions . 9
4 Principle .13
5 Apparatus .15
6 Specimen preparation.17
7 Testing conditions.17
8 Calculation of results .21
9 Precision and accuracy.25
10 Test report.25
Annex A (informative) Explanation of AC loss measurement with Poynting’s vector .31
Annex B (informative) Estimation of geometrical error in the pickup coil method .33
Annex C (informative) Recommended method for calibration of magnetization and
AC loss .35
Annex D (informative)  Coupling loss for various types of applied magnetic field .39
Annex E (informative)  Extension to three-component superconducting wires.41
Bibliography.43
Figure 1 – Standard arrangement of the specimen and pickup coils .29
Figure 2 – A typical electrical circuit for AC loss measurement by pickup coils .29
Figure B.1 − Examples of calculated contour line map of the coefficient G for a
radius R of the coiled specimen and a difference a between radii of the specimen and
each pickup coil .33
Figure C.1 − Evaluation of critical field from magnetization curves .37
Figure D.1 – Waveforms of applied magnetic field with a period T.39

61788-8 © IEC:2003 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
__________
SUPERCONDUCTIVITY –
Part 8: AC loss measurements –
Total AC loss measurement of Cu/Nb-Ti composite
superconducting wires exposed to a transverse alternating
magnetic field by a pickup coil method
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the 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, the IEC publishes International Standards. Their preparation is
entrusted to technical committees; any IEC National Committee interested in the subject dealt with may
participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. The IEC collaborates closely with the International
Organization for Standardization (ISO) in accordance with conditions determined by agreement between the
two organizations.
2) The formal decisions or agreements of the 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 National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical specifications, technical reports or guides and they are accepted by the National
Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61788-8 has been prepared by IEC technical committee 90:
Superconductivity.
The text of this standard is based on the following documents:
FDIS Report on voting
90/135A/FDIS 90/140/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged
until 2008. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
61788-8 © IEC:2003 – 7 –
INTRODUCTION
Magnetometer and pickup coil methods are proposed for measuring the AC losses of Cu/Nb-
Ti composite superconducting wires in transverse time-varying magnetic fields. These
represent initial steps in standardization of methods for measuring the various contributions to
AC loss in transverse fields, the most frequently encountered configuration.
It was decided to split the initial proposal mentioned above, into two documents covering two
standard methods. One of them describes the magnetometer method for hysteresis loss and
low frequency (or sweep rate) total AC loss measurement in a slowly varying magnetic field,
and the other describes the pickup coil method for total AC loss measurement in higher
frequency (or sweep rate) magnetic fields. The frequency range is 0 Hz to 0,06 Hz for the
magnetometer method and 0,005 Hz to 1 Hz for the pickup coil method. The overlap between
0,005 Hz and 0,06 Hz is a complementary frequency range for the two methods.
This standard covers the pickup coil method. The test method for standardization of AC loss
covered in this standard is partly based on the Versailles Project on Advanced Materials and
Standards (VAMAS) pre-standardization work on the AC loss of NbTi composite super-
conductors [1] .
___________
Figures in square brackets refer to the Bibliography.

61788-8 © IEC:2003 – 9 –
SUPERCONDUCTIVITY –
Part 8: AC loss measurements –
Total AC loss measurement of Cu/Nb-Ti composite
superconducting wires exposed to a transverse alternating
magnetic field by a pickup coil method
1 Scope
This part of IEC 61788-8 specifies the measurement method of total AC losses by the pickup
coil method in Cu/Nb-Ti composite superconducting wires exposed to a transverse alternating
magnetic field. The losses may contain both hysteresis and coupling losses. The standard
method to measure only the hysteresis loss in DC or low-sweep-rate magnetic field is
specified in IEC 61788-13 [2].
The specimen shall be a multifilamentary round or rectangular wire, expected to be mainly
used for pulsed coil applications with relatively higher frequencies or sweep rates up to 1 Hz
or 4 T/s, with diameter or average size from 0,2 mm to 1,0 mm, filament diameter from 1 µm
to around 50 µm, and a coupling time constant less than about 40 ms.
The present method can be also extended to the AC loss measurement in a higher range of
frequency and sweep rate up to more than 10 Hz or 40 T/s for three-component
superconducting wires (IEV 815-04-33) with a shorter coupling time constant down to about
0,1 ms (see Annex E).
2 Normative references
The following referenced documents are indispensable 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, International Electrotechnical Vocabulary (IEV) – Part 815: Superconductivity
3 Terms and definitions
For the purposes of this part of IEC 61788, the definitions of IEC 60050-815 and the following
apply.
3.1
AC loss
P
power dissipated in a composite superconductor due to application of time-varying magnetic
field or current
[IEV 815-04-54]
61788-8 © IEC:2003 – 11 –
3.2
hysteresis loss
P
h
loss of the type whose value per cycle is independent of frequency arising in a super-
conductor under a varying magnetic field
NOTE This loss is caused by the irreversible magnetic properties of the superconducting material due to pinning
of flux lines.
[IEV 815-04-55]
3.3
eddy current loss
P
e
loss arising in the normal matrix of a composite superconductor or the structural material
when exposed to a varying magnetic field, either from an applied field or from a self-field
[IEV 815-04-56, modified]
3.4
(filament) coupling (current) loss
P
c
loss arising in multi-filamentary superconducting wires with a normal matrix due to coupling
current
[IEV 815-04-59]
3.5
coupling time constant
ττττ
characteristic time constant of coupling current directed perpendicularly to filaments within
a strand for low frequencies
[IEV 815-04-60]
3.6
shielding current
current induced by a change of external magnetic field applied to a superconductor and which
includes coupling current and eddy current in composite superconductors
3.7
critical field strength
H
c
magnetic field strength corresponding to the superconducting condensation energy at zero
magnetic field strength
[IEV 815-01-21]
3.8
magnetization of a superconductor
magnetic moment divided by the volume of the superconductor
NOTE The macroscopic magnetic moment is also equal to the product of the shielding current and the area of
the closed path in a composite superconductor together with the magnetic moment of any penetrated trapped flux.

61788-8 © IEC:2003 – 13 –
3.9
magnetization method for AC loss
method to determine the AC loss of materials from the area of the loop of the magnetization
curve
NOTE When pickup coils are used to measure the change in flux, which is then integrated to get the
magnetization of stationary coiled specimens, the method is called the pickup coil method.
[IEV 815-08-15, modified]
3.10
pickup coil method
method to determine the AC loss of materials by evaluating electromagnetic power flow into
the materials by pickup coils
NOTE The pickup coil arrangement consists essentially of a primary winding (a superconducting magnet supplied
with a time varying current) and a pair of secondary windings (pickup coils), one of which (the main pickup coil)
contains the specimen to be measured and the other (the compensation coil) plays two roles: 1) it compensates the
signal from the main pickup coil when empty; 2) it supplies the field sweep information.
Here the coaxial and concentric arrangement of the pickup coils as shown in Figure 1 is used as the standard one
for the AC loss measurement. In order to obtain sufficient volume of the wire specimen to be measured and at the
same time to expose it to a transverse magnetic field, it must be wound into a coil. The specimen so prepared is
also referred to as the “coiled specimen”.
3.11
background loss
apparent loss obtained by the pickup coil method in the case where no specimen is located
inside the pickup coils
NOTE The background loss gives the experimental error in the system of the AC loss measurement by the pickup
coil method. It results from phase shift of electrical signal in the compensation process, an additional magnetic
moment induced in many components of experimental hardware, and imbalance in the pickup coils.
3.12
effective cross-sectional area of the coiled specimen
total specimen volume divided by the larger of the specimen coil height or the pickup coil
height
3.13
bending strain
εεεε
b
strain in percent arising from pure bending defined as ε = 100 r / R, where r is a half of
b
the specimen thickness and R is the bending radius
[IEV 815-08-03]
4 Principle
The test consists of applying an alternating transverse magnetic field to a specimen and
detecting the magnetic moment of shielding currents induced in the specimen by means of
pickup coils for the purpose of estimating the AC losses defined in Clause 3.

61788-8 © IEC:2003 – 15 –
5 Apparatus
5.1 Testing apparatus
The testing apparatus shall be constructed such that the pickup coils and a coiled specimen
are arranged in a uniform alternating magnetic field applied by a superconducting magnet.
The coils of the testing apparatus are arranged as described below. Typically, the main pickup
and compensation coils are coaxially positioned on the outside and inside of the coiled
specimen, respectively.
The applied alternating magnetic field shall have a high uniformity as shown in 7.1.5.
The testing apparatus has a sub-system that calculates the magnetization and the AC loss of
the specimen by integrating the signal of the pickup coils. A typical electrical circuit for the AC
loss measurement is given in Figure 2.
5.2 Pickup coils
Pickup coils shall be made of very fine insulated wire, such as insulated copper wire with
a diameter of 0,1 mm, to avoid eddy currents at low temperatures.
The pickup coil forms shall be made of non-metallic and non-magnetic material such as glass
fiber reinforced plastic, phenol resin, etc.
The main pickup coil shall be arranged coaxially and adjusted concentrically outside the
compensation coil. The standard arrangement is shown schematically in Figure 1, where the
height of the compensation coil is the same as that of the main pickup coil. The number of
turns in the compensation coil shall be usually adjusted to be a little larger than the balance
level in which the total interlinkage flux of the applied magnetic field into the compensation
coil is equal to that into the main pickup coil.
The pickup coil system shall be constructed so that the coiled specimen can be taken in and
out easily from the system.
The pickup coil method has geometrical error in relation with the arrangement of the coiled
specimen and the pickup coils. The geometrical error is mentioned briefly in Annex B. For a
reduced geometrical error of less than 1 %, the following arrangement for the coiled specimen
and the two pickup coils shall be the standard one; a height of 30 mm for the coiled specimen,
a height of 10 mm for the pickup coils, a coil radius of 18 mm for the specimen, and a
difference 2 mm between the radii of the specimen and each pickup coil. In the case where
the arrangement of the specimen and pickup coils are a little different from the above
standard one, the geometrical error in the arrangement shall be estimated, as shown in
Annex B. If the geometrical error cannot be estimated quantitatively, the calibration
indicated in Annex C may need to be performed.
5.3 Compensation circuit
The total interlinkage flux of the applied field in the compensation coil is usually a little larger
than that in the main pickup coil by adjusting the number of turns. The signal from the main
pickup coil is counterbalanced against a reduced signal of the compensation coil by means of
the compensation circuit. For delicate adjustment of the reduction ratio, called the
–4 –5
compensation coefficient, the compensation circuit has an accuracy of 10 to 10 to modify
the signal without a phase shift. For the conditions mentioned above, the compensation circuit
usually has the structure of a resistive potential divider.

61788-8 © IEC:2003 – 17 –
6 Specimen preparation
6.1 Coiled specimen
6.1.1 Winding of specimen
A coil form shall be used to wind the specimen into a single-layer solenoidal coil. When the
specimen has an insulation layer, the turns of the coil shall be tightly wound right next to
adjacent turns. When the specimen surface is not coated with an insulating material, the
specimen shall be wound with an equal space between turns by inserting a non-metallic and
non-magnetic spacer such as a fishing line to achieve turn-to-turn insulation of the specimen.
The diameter of the spacer shall be approximately half the specimen diameter.
6.1.2 Configuration of coiled specimen
The coil height of the specimen shall be more than three times as high as that of the pickup
coil in order to reduce geometrical error coming from the end effects of the coiled specimen.
6.1.3 Maximum bending strain
The maximum bending strain induced in the winding of the specimen shall not exceed 5
...