Superconductivity - Part 26: Critical current measurement - DC critical current of RE-Ba-Cu-O composite superconductors (IEC 61788-26:2020)

This part of IEC 61788 specifies a test method for determining the DC critical current of short
RE (rare earth)-Ba-Cu-O (REBCO) composite superconductor specimens that have a shape of
straight flat tape. This document applies to test specimens shorter than 300 mm and having a
rectangular cross section with an area of 0,03 mm2 to 7,2 mm2, which corresponds to tapes
with width ranging from 1,0 mm to 12,0 mm and thickness from 0,03 mm to 0,6 mm.
This method is intended for use with superconductor specimens that have critical current less
than 300 A and n-values larger than 5 under standard test conditions: the test specimen is
immersed in liquid nitrogen bath at ambient pressure without external magnetic field during the
testing. Deviations from this test method that are allowed for routine tests and other specific
restrictions are given in this document.

Supraleitfähigkeit - Teil 26: Messung des kritischen Stroms - Kritischer DC-Strom von RE-Ba-Cu-O-Kompositsupraleitern (IEC 61788-26:2020)

Supraconductivité - Partie 26: Mesurage du courant critique - Courant critique continu des composites supraconducteurs de RE-Ba-Cu-O (IEC 61788-26:2020)

L’IEC 61788-26:2020 spécifie une méthode d'essai pour la détermination du courant critique continu des échantillons de composites supraconducteurs RE (terre rare)-Ba-Cu-O (REBCO) courts en forme de ruban plat et rectiligne. Le présent document s'applique aux échantillons d’essai d'une longueur inférieure à 300 mm et d'une superficie de section rectangulaire de 0,03 mm2 à 7,2 mm2, ce qui correspond aux rubans d’une largeur de 1,0 mm à 12,0 mm et d’une épaisseur de 0,03 mm à 0,6 mm. Cette méthode est destinée à être utilisée avec des échantillons de supraconducteurs caractérisés par un courant critique inférieur à 300 A et des valeurs n supérieures à 5 dans les conditions d’essai normalisées: l’échantillon d’essai est immergé dans un bain d’azote liquide à pression ambiante sans champ magnétique externe pendant l’essai. Le présent document spécifie les écarts par rapport à cette méthode d’essai qui sont admis dans les essais individuels de série, ainsi que d'autres restrictions spécifiques.

Superprevodnost - 26. del: Meritve kritičnega toka - Enosmerni kritični tok pri superprevodnikih iz kompozita RE-Ba-Cu-O (IEC 61788-26:2020)

General Information

Status
Published
Publication Date
02-Sep-2020
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
12-Aug-2020
Due Date
17-Oct-2020
Completion Date
03-Sep-2020

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SLOVENSKI STANDARD
SIST EN IEC 61788-26:2020
01-oktober-2020
Superprevodnost - 26. del: Meritve kritičnega toka - Enosmerni kritični tok pri
superprevodnikih iz kompozita RE-Ba-Cu-O (IEC 61788-26:2020)

Superconductivity - Part 26: Critical current measurement - DC critical current of RE-Ba-

Cu-O composite superconductors (IEC 61788-26:2020)

Supraleitfähigkeit - Teil 26: Messung des kritischen Stroms - Kritischer DC-Strom von

RE-Ba-Cu-O-Kompositsupraleitern (IEC 61788-26:2020)

Supraconductivité - Partie 26: Mesurage du courant critique - Courant critique continu

des composites supraconducteurs de RE-Ba-Cu-O (IEC 61788-26:2020)
Ta slovenski standard je istoveten z: EN IEC 61788-26:2020
ICS:
17.220.20 Merjenje električnih in Measurement of electrical
magnetnih veličin and magnetic quantities
29.050 Superprevodnost in prevodni Superconductivity and
materiali conducting materials
SIST EN IEC 61788-26:2020 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN IEC 61788-26:2020
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SIST EN IEC 61788-26:2020
EUROPEAN STANDARD EN IEC 61788-26
NORME EUROPÉENNE
EUROPÄISCHE NORM
August 2020
ICS 17.220.20; 19.080; 29.050
English Version
Superconductivity - Part 26: Critical current measurement - DC
critical current of RE-Ba-Cu-O composite superconductors
(IEC 61788-26:2020)

Supraconductivité - Partie 26: Mesurage du courant critique Supraleitfähigkeit - Teil 26: Messung des kritischen Stroms

- Courant critique continu des composites - Kritischer DC-Strom von RE-Ba-Cu-O Komposit

supraconducteurs de RE-Ba-Cu-O Supraleitern
(IEC 61788-26:2020) (IEC 61788-26:2020)

This European Standard was approved by CENELEC on 2020-07-16. 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, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the

Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, 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

© 2020 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.

Ref. No. EN IEC 61788-26:2020 E
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SIST EN IEC 61788-26:2020
EN IEC 61788-26:2020 (E)
European foreword

The text of document 90/455/FDIS, future edition 1 of IEC 61788-26, prepared by IEC/TC 90

"Superconductivity" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as

EN IEC 61788-26:2020.
The following dates are fixed:

• latest date by which the document has to be implemented at national (dop) 2021-04-16

level by publication of an identical national standard or by endorsement

• latest date by which the national standards conflicting with the (dow) 2023-07-16

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 61788-26:2020 was approved by CENELEC as a European

Standard without any modification.
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SIST EN IEC 61788-26:2020
EN IEC 61788-26:2020 (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 - International Electrotechnical Vocabulary - - -
Part 815: Superconductivity
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SIST EN IEC 61788-26:2020
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SIST EN IEC 61788-26:2020
IEC 61788-26
Edition 1.0 2020-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Superconductivity –
Part 26: Critical current measurement – DC critical current of RE-Ba-Cu-O
composite superconductors
Supraconductivité –
Partie 26: Mesurage du courant critique – Courant critique continu des
composites supraconducteurs de RE-Ba-Cu-O
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.220.20; 19.080; 29.050 ISBN 978-2-8322-8436-0

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 61788-26:2020
– 2 – IEC 61788-26:2020 © IEC 2020
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 Critical current measuring system ........................................................................... 8

6 Specimen preparation and setup ..................................................................................... 8

6.1 Length .................................................................................................................... 8

6.2 Mounting of the specimen ....................................................................................... 9

7 Critical current measurement ........................................................................................... 9

8 Calculation of results ....................................................................................................... 9

8.1 Critical current criteria............................................................................................. 9

8.2 n-value (optional) .................................................................................................. 11

9 Uncertainty of measurement .......................................................................................... 11

10 Test report ..................................................................................................................... 11

10.1 Identification of test specimen ............................................................................... 11

10.2 Reporting of I values ........................................................................................... 11

10.3 Reporting of I test conditions ............................................................................... 11

Annex A (informative) Additional information relating to measurement, apparatus, and

calculation ............................................................................................................................ 12

A.1 General information .............................................................................................. 12

A.2 Measurement condition ......................................................................................... 12

A.3 Apparatus ............................................................................................................. 13

A.3.1 Measurement holder material ........................................................................ 13

A.3.2 Measurement holder construction .................................................................. 13

A.4 Specimen preparation ........................................................................................... 14

A.5 Measurement procedure ....................................................................................... 14

A.5.1 Voltage leads ................................................................................................. 14

A.5.2 Cooling process ............................................................................................. 14

A.5.3 Temperature of liquid nitrogen bath ............................................................... 14

A.5.4 System noise and other contributions to the measured voltage ...................... 15

A.6 Calculation of n-value ........................................................................................... 16

Annex B (informative) Evaluation of combined standard uncertainty for REBCO

I measurement [8] ............................................................................................................... 17

B.1 Practical critical current measurement .................................................................. 17

B.2 Model equation ..................................................................................................... 18

B.3 I measurement results ......................................................................................... 19

B.4 Combined standard uncertainty [11] ...................................................................... 21

B.5 Type B uncertainty evaluation ............................................................................... 22

B.5.1 General ......................................................................................................... 22

B.5.2 Uncertainty of L measurement ...................................................................... 22

B.5.3 Uncertainty of voltage measurement .............................................................. 22

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SIST EN IEC 61788-26:2020
IEC 61788-26:2020 © IEC 2020 – 3 –

B.5.4 Uncertainty of current measurement .............................................................. 23

B.5.5 Uncertainty of temperature measurement ...................................................... 23

B.5.6 Uncertainty coming from intrinsic non-uniformity of I .................................... 24

B.5.7 Comparison between types A and B combined standard uncertainties ........... 25

B.6 Influence of current ramp rate on the total uncertainty .......................................... 26

Bibliography .......................................................................................................................... 27

Figure 1 – Schematic view of measurement setup ................................................................... 9

Figure 2 – Intrinsic U-I characteristic .................................................................................... 10

Figure 3 – U-I curve with a current transfer component ......................................................... 10

Figure A.1 – Illustration of a measurement configuration for a short specimen of a few

hundred amperes class REBCO conductor ........................................................................... 13

Figure A.2 – Temperature dependence of I for commercial REBCO superconductors

(data from [9]) ....................................................................................................................... 14

Figure A.3 – Pressure dependence of boiling temperature of liquid nitrogen ......................... 15

Figure B.1 – Typical circuit to measure I .............................................................................. 17

Figure B.2 – Typical voltage–current (U-I) characteristic of a superconductor ....................... 18

Figure B.3 – Ramp time dependence of total RSU of I for conductors B, C, and D ............... 26

Table A.1 – Thermal contraction data of superconductor

and sample‑holder materials [1] ............................................................................................ 13

Table B.1 – Conductors distributed in the international RRT ................................................. 19

Table B.2 – I data for conductor A ....................................................................................... 19

Table B.3 – I data for conductor B ....................................................................................... 20

Table B.4 – I data for conductor C ....................................................................................... 20

Table B.5 – I data for conductor D ....................................................................................... 20

Table B.6 – Statistics for each conductor .............................................................................. 21

Table B.7 – ANOVA results for each conductor ..................................................................... 21

Table B.8 – Atmospheric pressure from 1 January 2014 to 31 December 2014 ..................... 24

Table B.9 – Intrinsic I non-uniformity evaluated by RTR-SHPM ........................................... 24

Table B.10 – Budget table of SUs of I measurements for conductor C ................................. 25

Table B.11 – Comparison of the relative standard uncertainties for

conductors B, C, and D ......................................................................................................... 25

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SIST EN IEC 61788-26:2020
– 4 – IEC 61788-26:2020 © IEC 2020
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SUPERCONDUCTIVITY –
Part 26: Critical current measurement –
DC critical current of RE-Ba-Cu-O composite superconductors
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, Technical Reports,

Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). 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. 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 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

Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC

Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

misinterpretation by any end user.

4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

transparently to the maximum extent possible in their national and regional publications. Any divergence between

any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.

5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity

assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any

services carried out by independent certification bodies.

6) All users should ensure that they have the latest edition of this publication.

7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

members of its technical committees and IEC National Committees for any personal injury, property damage or

other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and

expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publications.

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 61788-26 has been prepared by IEC technical committee
90: Superconductivity.
The text of this standard is based on the following documents:
FDIS Report on voting
90/455/FDIS 90/458/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.

---------------------- Page: 10 ----------------------
SIST EN IEC 61788-26:2020
IEC 61788-26:2020 © IEC 2020 – 5 –

A list of all parts in the IEC 61788 series, published under the general title Superconductivity,

can be found on the IEC website.

The committee has decided that the contents of this publication will remain unchanged until the

stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data related to

the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
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SIST EN IEC 61788-26:2020
– 6 – IEC 61788-26:2020 © IEC 2020
INTRODUCTION

In 1986, superconductivity in some perovskite type materials containing copper oxides at

temperatures far above the critical temperatures of metallic superconductors was discovered.

In 1987, it was discovered that Y-Ba-Cu-O (YBCO) has a critical temperature (T ) of 93 K. After

a quarter century, the RE-Ba-Cu-O (REBCO, RE = rare earth) superconductors became

commercially available.

In 2013, VAMAS-TWA 16 started working on the critical current measurement methods in

REBCO superconductors. In 2014, an international round robin test (RRT) on the critical current

measurement method for REBCO superconductors was conducted that was led by VAMAS-

TWA 16. 10 institutions/universities/industries from five countries participated. The pre-

standardization work of VAMAS was taken as a base for this document, on the DC critical

current test method of REBCO composite superconductors.

The test method covered in this document is intended to give an appropriate and accepted

technical base to engineers working in the field of superconductivity technology.

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SIST EN IEC 61788-26:2020
IEC 61788-26:2020 © IEC 2020 – 7 –
SUPERCONDUCTIVITY –
Part 26: Critical current measurement –
DC critical current of RE-Ba-Cu-O composite superconductors
1 Scope

This part of IEC 61788 specifies a test method for determining the DC critical current of short

RE (rare earth)-Ba-Cu-O (REBCO) composite superconductor specimens that have a shape of

straight flat tape. This document applies to test specimens shorter than 300 mm and having a

2 2

rectangular cross section with an area of 0,03 mm to 7,2 mm , which corresponds to tapes

with width ranging from 1,0 mm to 12,0 mm and thickness from 0,03 mm to 0,6 mm.

This method is intended for use with superconductor specimens that have critical current less

than 300 A and n-values larger than 5 under standard test conditions: the test specimen is

immersed in liquid nitrogen bath at ambient pressure without external magnetic field during the

testing. Deviations from this test method that are allowed for routine tests and other specific

restrictions are given in this document.
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, International Electrotechnical Vocabulary (IEV) – Part 815: Superconductivity

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 URLs:

• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp/
3.1
constant sweep rate method

U-I data acquisition method where a current is swept at a constant rate from zero to a current

above I , and where the U-I data are acquired continuously or frequently
3.2
ramp-and-hold method

U-I data acquisition method where a current is swept in stages from zero to a current above I ,

where the current is held for an appropriate amount of time at each stage, and where the U-I

data are acquired continuously or frequently
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SIST EN IEC 61788-26:2020
– 8 – IEC 61788-26:2020 © IEC 2020
4 Principle

The critical current of a composite superconductor specimen shall be determined from a

voltage–current (U-I) characteristic measured in a liquid nitrogen bath at ambient pressure. To

get a U-I characteristic, a direct current is applied to the superconductor specimen and the

voltage generated along the specimen is measured. The current is increased from zero and the

U-I characteristic is recorded. The critical current shall be determined as the current at which a

specific electric field strength criterion (electric field criterion) (E ) is reached. For any selected

, there shall be a corresponding voltage criterion (U ) for a specified voltage tap separation.

c c
5 Apparatus
5.1 General

The apparatus required for the present test method includes the critical current measuring

system. Additional information relating to the apparatus is given in Annex A.
5.2 Critical current measuring system

The apparatus to measure the U-I characteristic should consist of a specimen probe, an open

bath and a U-I measurement system.

The specimen probe, which consists of a specimen and a measurement holder, is inserted in

the open bath filled with liquid nitrogen. The U-I measurement system consists of a DC current

source and necessary data acquisition system, preamplifiers, filters or voltmeters, or a

combination thereof. Suitable measurement holder materials are recommended in A.3.1.

A computer assisted data acquisition system is recommended.
6 Specimen preparation and setup
6.1 Length
An example of a schematic view of measurement setup is shown in Figure 1.
The length (L) of specimen to be measured shall be defined as follows:
L = L + 2 × L + 2 × L + L ≥ 5 × W (1)
1 2 3 4
L , L , L ≥ W (2)
1 2 3
where
L is the distance between the voltage taps;
L is the length of the current contact;

L is the shortest distance from a current contact to the neighbouring voltage tap;

L is the width of a voltage tap.
W is the width of a specimen to be measured.

The larger the current-carrying capacity of the specimen, the larger shall be L . L shall be

2 2

increased for a specimen that has a stainless steel or other high-resistivity material backing or

jacket. For a measurement that needs the higher voltage sensitivity, L shall be increased. For

some practical values for L through L , see A.3.2.
1 4
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SIST EN IEC 61788-26:2020
IEC 61788-26:2020 © IEC 2020 – 9 –
Figure 1 – Schematic view of measurement setup
6.2 Mounting of the specimen

The specimen shall be mounted to the flat surface of the holder. Both ends shall be fastened

or soldered to the current contact blocks.
The voltage taps shall be placed in the central part with or without solder.

The current contacts and the voltage taps shall be on the superconducting layer side.

Voltage leads shall be twisted as close to the voltage taps as possible.
7 Critical current measurement
The critical current shall be measured while minimizing mechanical strain.

The specimen shall be inserted slowly into the liquid nitrogen bath. The volume of the liquid

nitrogen bath shall be sufficiently larger than the specimen and the measurement holder. The

depth of the bath shall be sufficiently higher than the height of the measurement holder. The

specimen shall be cooled from room temperature to liquid nitrogen temperature until the

specimen and the measurement holder are sufficiently cooled by liquid nitrogen that boils with

microbubbles, i.e. steady state. It takes several tens of seconds.

When using the constant sweep rate method, the sweep rate shall be selected not to influence

the voltage measurement.

When using the ramp-and-hold method, the current sweep rate between stages shall be lower

than the equivalent of ramping from zero current to I in 3 s. Data acquisition at each stage

shall be started as soon as the flow or creep voltage generated by the current ramp can be

disregarded. The current drift during each current set point shall be less than 1 % of I .

Record the U-I characteristic with increasing current.
After measurement, the specimen shall be warmed up to room temperature.
Additional information relating to the measurement is given in Annex A.
8 Calculation of results
8.1 Critical current criteria

The critical current I shall be determined by using an electric field criterion E .

c c
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SIST EN IEC 61788-26:2020
– 10 – IEC 61788-26:2020 © IEC 2020
I shall be determined at E = 100 μV/m. I determined at E = 10 μV/m is optional.
c c c c

The I shall be determined as the current corresponding to the point on the U-I curve where the

voltage U is measured (see Figure 2 and Figure 3):
U = L E (3)
c 1 c
where
U is the voltage criterion in microvolts (μV);
L is the voltage tap separation in metres (m);
E is the electric field criterion in microvolts per metre (μV/m).

U and I are the corresponding voltage and current values at the intersecting point of the

c c
straight lines with the U-I curve as shown in Figure 2.
Figure 2 – Intrinsic U-I characteristic

If the measured U-I curve includes a resistive component, it is recommended to increase L to

minimize the current transfer component voltage.
Figure 3 – U-I curve with a current transfer component
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SIST EN IEC 61788-26:2020
IEC 61788-26:2020 © IEC 2020 – 11 –
8.2 n-value (optional)

The n-value shall be calculated as the slope of the plot of log U versus log I in the region where

the I is determined. The corresponding electric field region is recommended to be from 10 µV/m

to 100 µV/m.
The electric field region used to determine the n-value shall be reported.
Additional information relating to the calculation is given in Annex A.
9 Uncertainty of measurement

Unless otherwise specified, measurements shall be carried out in a liquid nitrogen bath whose

temperature can range from 76,8 K to 77
...

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