Electrical safety in low voltage distribution systems up to 1 000 V AC and 1 500 V DC - Equipment for testing, measuring or monitoring of protective measures - Part 3: Loop impedance

IEC 61557-3:2019 is available as IEC 61557-3:2019 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.IEC 61557-3:2019 specifies the requirements applicable to equipment for measuring the loop impedance between a line conductor and protective conductor; between a line conductor and neutral; or between two line conductors by using the voltage drop when the circuit under test is loaded. IEC 61557-3:2019 cancels and replaces the second edition published in 2007. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
a) addition of equirements as regards the measurement category;
b) addition of new requirements for operating instructions;
c) alignment of the structure with that of the whole IEC 61557 series.

Sécurité électrique dans les réseaux de distribution basse tension au plus égale à 1 000 V c.a. et 1 500 V c.c. - Dispositifs de contrôle, de mesure ou de surveillance de mesures de protection - Partie 3: Impédance de boucle

IEC 61557-3:2019 est disponible sous forme de IEC 61557-3:2019 RLV qui contient la Norme internationale et sa version Redline, illustrant les modifications du contenu technique depuis l'édition précédente.L'IEC 61557-3:2019 spécifie les exigences applicables aux appareils destinés à mesurer l'impédance de boucle entre un conducteur de ligne et le conducteur de protection, entre un conducteur de ligne et le conducteur neutre, ou entre deux conducteurs de ligne en utilisant la chute de tension lorsque le circuit en essai est chargé. L'IEC 61557-3:2019 annule et remplace la deuxième édition parue en 2007. Cette édition constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
a) ajout d'une exigence relative à la catégorie de mesure;
b) ajout de nouvelles exigences relatives aux instructions de fonctionnement;
c) alignement de la structure sur l'ensemble de la série IEC 61557.

General Information

Status
Published
Publication Date
25-Jul-2019
Current Stage
PPUB - Publication issued
Completion Date
26-Jul-2019
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IEC 61557-3
Edition 3.0 2019-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electrical safety in low voltage distribution systems up to 1 000 V a.c. and
1 500 V d.c. – Equipment for testing, measuring or monitoring of protective
measures –
Part 3: Loop impedance
Sécurité électrique dans les réseaux de distribution basse tension au plus égale
à 1 000 V c.a. et 1 500 V c.c. – Dispositifs de contrôle, de mesure ou de
surveillance de mesures de protection –
Partie 3: Impédance de boucle
IEC 61557-3:2019-07(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 61557-3
Edition 3.0 2019-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electrical safety in low voltage distribution systems up to 1 000 V a.c. and
1 500 V d.c. – Equipment for testing, measuring or monitoring of protective
measures –
Part 3: Loop impedance
Sécurité électrique dans les réseaux de distribution basse tension au plus égale
à 1 000 V c.a. et 1 500 V c.c. – Dispositifs de contrôle, de mesure ou de
surveillance de mesures de protection –
Partie 3: Impédance de boucle
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.220.20; 29.080.01; 29.240.01 ISBN 978-2-8322-7156-8

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
---------------------- Page: 3 ----------------------
– 2 – IEC 61557-3:2019 © IEC 2019
CONTENTS

FOREWORD ........................................................................................................................... 3

1 Scope .............................................................................................................................. 5

2 Normative references ....................................................................................................... 5

3 Terms and definitions....................................................................................................... 5

4 Requirements .................................................................................................................. 6

4.1 General ................................................................................................................... 6

4.2 Measurement of loop impedance ............................................................................. 6

4.3 External resistance .................................................................................................. 6

4.4 Fault voltage exceeding U ..................................................................................... 7

4.5 Overvoltage ............................................................................................................ 7

5 Marking and operating instructions ................................................................................... 7

5.1 Marking ................................................................................................................... 7

5.2 Operating instructions ............................................................................................. 7

6 Tests ............................................................................................................................... 8

6.1 General ................................................................................................................... 8

6.2 Operating uncertainty .............................................................................................. 8

6.3 External resistance ................................................................................................ 10

6.4 Fault voltage ......................................................................................................... 10

6.5 Overvoltage .......................................................................................................... 10

Bibliography .......................................................................................................................... 11

Table 1 – Calculation of operating uncertainty ......................................................................... 9

---------------------- Page: 4 ----------------------
IEC 61557-3:2019 © IEC 2019 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICAL SAFETY IN LOW VOLTAGE DISTRIBUTION SYSTEMS
UP TO 1 000 V AC AND 1 500 V DC –
EQUIPMENT FOR TESTING, MEASURING OR MONITORING
OF PROTECTIVE MEASURES –
Part 3: Loop impedance
FOREWORD

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patent rights. IEC shall not be held responsible for identifying any or all such patent rights.

International Standard IEC 61557-3 has been prepared by IEC technical committee 85:

Measuring equipment for electrical and electromagnetic quantities.

This third edition cancels and replaces the second edition published in 2007. This edition

constitutes a technical revision.

This edition includes the following significant technical changes with respect to the previous

edition:
a) addition of equirements as regards the measurement category;
b) addition of new requirements for operating instructions;
c) alignment of the structure with that of the whole IEC 61557 series.
---------------------- Page: 5 ----------------------
– 4 – IEC 61557-3:2019 © IEC 2019
The text of this International Standard is based on the following documents:
FDIS Report on voting
85/687/FDIS 85/694/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.

This International Standard is to be used in conjunction with IEC 61557-1:2019.

A list of all parts in the IEC 61557 series, published under the general title Electrical safety in

low voltage distribution systems up to 1 000 V AC and 1 500 V DC – Equipment for testing,

measuring or monitoring of protective measures, can be found on the IEC website.

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.
---------------------- Page: 6 ----------------------
IEC 61557-3:2019 © IEC 2019 – 5 –
ELECTRICAL SAFETY IN LOW VOLTAGE DISTRIBUTION SYSTEMS
UP TO 1 000 V AC AND 1 500 V DC –
EQUIPMENT FOR TESTING, MEASURING OR MONITORING
OF PROTECTIVE MEASURES –
Part 3: Loop impedance
1 Scope

This part of IEC 61557 specifies the requirements applicable to equipment for measuring the

loop impedance between a line conductor and protective conductor; between a line conductor

and neutral; or between two line conductors by using the voltage drop when the circuit under

test is loaded.
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 61010-1:2010, Safety requirements for electrical equipment for measurement, control, and

laboratory use – Part 1: General requirements
IEC 61010-1:2010/AMD1:2016

IEC 61010-2-030:2017, Safety requirements for electrical equipment for measurement, control,

and laboratory use – Part 2-030: Particular requirements for equipment having testing or

measuring circuits

IEC 61557-1:2019, Electrical safety in low voltage distribution systems up to 1 000 V AC and

1 500 V DC – Equipment for testing, measuring or monitoring of protective measures – Part 1:

General requirements
3 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC 61557-1 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
loading

method of applying a load to a circuit within a distribution system to cause a voltage drop

__________

A consolidated version of this publication exists, comprising IEC 61010-1:2010 and

IEC 61010-1:2010/AMD1:2016.
---------------------- Page: 7 ----------------------
– 6 – IEC 61557-3:2019 © IEC 2019
3.2
loading equipment
part of the measuring equipment to load the circuit being tested
3.3
test current

electric current controlled by the measuring device to cause a voltage drop in a circuit being

tested
3.4
system phase angle
angle between loop impedance and loop resistance of the distribution system
3.5
loop impedance

sum of the impedances in a current loop comprising the impedance of the source of the current

and the impedance of the line conductor (e.g. protective conductor, earth electrode and earth)

from the point of measurement to the other terminal of the source of the current
4 Requirements
4.1 General

In addition to the requirements of IEC 61557-1:2019, Clause 4, the requirements of Clause 4 of

this document shall apply.

Equipment intended to be used on the distribution system shall, at the minimum, be rated

measurement category III according to IEC 61010-2-030.

Equipment intended to be used on socket outlets only can be rated for measurement category

II according to IEC 61010-2-030.
4.2 Measurement of loop impedance

For measurements in close proximity to the transformer of the distribution system, equipment

with a specified loop impedance measuring function (influence quantity for system phase angle

at a minimum of 30°) shall be used or a specified additional operating uncertainty shall be

taken into account by the user.

In applications where the measurement of loop resistance is carried out in close proximity to

the sourcing transformer (e.g. < 50 m) the system phase angle may be greater than 18° (e.g.

up to 30°) and therefore the inductive part of the internal impedance of the transformer may not

be negligible.

When the loading by loading equipment causes transients on the distribution system, the

operating uncertainty shall not be exceeded as a result of the transient.

Equipment with specified influence quantity E of system phase angle of approximately 18°

6.1

shall be marked with the warning symbol according to IEC 61010-1:2010, Table 1, symbol 14,

adjacent to the loop function marking or a warning shall be given on the display.

4.3 External resistance

When external resistances are included in the calibration as a zero offset, this shall be

indicated on the measuring instrument.
---------------------- Page: 8 ----------------------
IEC 61557-3:2019 © IEC 2019 – 7 –

This offset shall remain included in the calibration as long as it is indicated on the measuring

instrument regardless of any changes in range or function.
4.4 Fault voltage exceeding U

Fault voltages as a result of a measurement that exceed U at the point of test shall be avoided.

This can be achieved by automatic disconnection in accordance with
IEC 61010-1:2010/AMD1:2016, Figure 2.
4.5 Overvoltage

The measuring equipment shall not be damaged nor shall the user be exposed to danger when

the measuring equipment is connected to 120 % of the nominal voltage of the distribution

system for which the measuring equipment has been designed. Protective devices of the test

equipment shall not be activated.

The user shall not be exposed to danger and the equipment shall not be damaged when the

measuring equipment is accidentally connected to a voltage having a value of 173 % of its

rated voltage to earth according to IEC 61010-2-030 for 1 min. Protective devices of the test

equipment can be activated.

If the measuring equipment indicates the value of the voltage at its measuring terminals, it

shall also indicate if the system voltage exists and if the live conductor is exchanged with the

protective conductor.
5 Marking and operating instructions
5.1 Marking

In addition to IEC 61557-1:2019, 5.1 and 5.2, the following information shall be provided on the

measuring equipment.
Marking is permitted on the display for any of the following:

– range of the resistance of the loop impedance or of the calculated short-circuit current

respectively within which compliance with the uncertainty limits in accordance with 4.2 is

maintained;
– nominal system voltage for which the equipment is rated;
– rated system frequency for which the equipment is rated;

– maximum system phase angle for which the equipment is designed when this angle is

greater than 18°;
– rated voltage to earth and measurement category.
5.2 Operating instructions

In addition to IEC 61557-1:2019, 5.3, the following information shall be provided in the

operating instructions for the measuring equipment:

– an explanation of the influence of the system phase angle on measurement accuracy;

– the amplitude and waveform of test current and duration of loading;

– range of system voltages within which the operating uncertainty stated in 6.2 is not

exceeded;

– range of loop impedance (magnitude and angle) within which the operating uncertainty

stated in 6.2 is not exceeded;

– information on possible measurement uncertainties, for example due to preloading the

circuit under test;
---------------------- Page: 9 ----------------------
– 8 – IEC 61557-3:2019 © IEC 2019

– data relating to the effect of system voltage variations and other effects from the system

such as measuring in close proximity to the transformer of the distribution system. A

specific user correction shall be stated, unless the instrument has a fully specified loop

impedance measuring function.
6 Tests
6.1 General

In addition to IEC 61557-1:2019, Clause 6, the following tests shall be performed.

6.2 Operating uncertainty

The operating uncertainty shall be determined under the rated operating conditions of

IEC 61557-1 and in addition the following shall apply:

– the electrical distribution system on which a loop impedance test is performed shall be

under constant load condition, except for load changes provoked by the test instrument;

– measurement shall be carried out without changing existing loads within the electrical

distribution system under test;

– system voltage shall be between 85 % and 110 % of the nominal voltage of the distribution

system for which the equipment has been designed;

– system frequency shall be between 99 % and 101 % of the nominal frequency of the

distribution system for which the equipment has been designed;

– system voltage and frequency shall not change during the measurement by more than

0,5 %;
– measured circuit shall be loaded with loading equipment.

The operating uncertainty shall be calculated in accordance with Table 1. In this process, the

intrinsic uncertainty shall be determined under the following reference conditions:

– nominal system voltage;
– nominal system frequency;
– reference temperature 23 °C ± 2 °C;
– reference position in accordance with the manufacturer's statement;
– nominal distribution system supply or battery voltage respectively;

– difference between the phase angle of the loading equipment and the loop impedance of

the circuit under test ≤ 5°.

– the maximum percentage operating uncertainty within the measuring range to be marked or

stated shall not exceed ±30 % with the measured value as the fiducial value, as determined

in accordance with Table 1.
---------------------- Page: 10 ----------------------
IEC 61557-3:2019 © IEC 2019 – 9 –
Table 1 – Calculation of operating uncertainty
Requirements or
Intrinsic
Reference conditions or Designation tests in accordance Type
uncertainty or
specified operating range code with relevant parts of test
influence quantity
of IEC 61557
Intrinsic uncertainty Reference conditions A IEC 61557-3:2019, 6.2 R
Position (on Reference position ±90° E IEC 61557-1:2019, R
equipment using approximately 6.2.2
mechanical
displays)
Supply voltage At the limits stated by the E IEC 61557-1:2019, R
manufacturer 6.2.4
Temperature 0 °C and 35 °C E IEC 61557-1:2019, T
(± 2°) 6.2.3
Phase angle At a phase angle 0° to 18° E IEC 61557-3:2019, 6.2 T
approximately
System phase angle At a system phase angle 0° to E IEC 61557-3:2019, 6.2 T
6.1
18° at the bottom of the
measurement range
System phase angle At a system phase angle 0° to E IEC 61557-3:2019, 6.2 T
6.2
30° at the bottom of the
measurement range
System frequency 95 % to 105 % of the nominal E IEC 61557-3:2019, 6.2 T
frequency
System voltage 85 % to 110 % of the nominal E IEC 61557-3:2019, 6.2 T
voltage
Harmonics 5 % of 3 harmonic at 0° phase IEC 61557-3:2019, 6.2 T
angle
6 % of 5 harmonic at 180°
phase angle
5 % of 7 harmonic at 0° phase
angle (percentage of the
fundamental of nominal voltage
of distribution system)
DC quantity Add additional DC quantities of E IEC 61557-3:2019, 6.2 T
0,5 % of the nominal voltage of
distribution system in both
polarities.
It is recommended that manufac-
turers include E into the
calculation of operating
uncertainty according to this
table.
Operating IEC 61557-3:2019, 6.2 R
uncertainty
BA=±+ E
Key
B% =±× 100 %
A = intrinsic uncertainty
E = variations
R = routine test
T = type test
F = fiducial value
Use E or E as applicable.
6.1 6.2

Influence quantity E takes into account possible voltage drops caused by DC leakage currents according to

IEC 61800-5-2 on the PE or PEN conductor.
---------------------- Page: 11 ----------------------
– 10 – IEC 61557-3:2019 © IEC 2019
6.3 External resistance

Compliance with the requirements in accordance with 4.3 shall be tested (type test).

6.4 Fault voltage

Compliance with the requirements in accordance with 4.4 shall be tested (routine test).

6.5 Overvoltage

The permissible overvoltage in accordance with the requirements of 4.5 shall be tested

(type test).
---------------------- Page: 12 ----------------------
IEC 61557-3:2019 © IEC 2019 – 11 –
Bibliography

IEC 61800-5-2, Adjustable speed electrical power drive systems – Part 5-2: Safety

requirements – Functional
___________
---------------------- Page: 13 ----------------------
– 12 – IEC 61557-3:2019 © IEC 2019
SOMMAIRE

AVANT-PROPOS .................................................................................................................. 13

1 Domaine d'application .................................................................................................... 15

2 Références normatives .................................................................................................. 15

3 Termes et définitions ..................................................................................................... 15

4 Exigences ...................................................................................................................... 16

4.1 Généralités ........................................................................................................... 16

4.2 Mesure de l'impédance de boucle .......................................................................... 16

4.3 Résistance externe ............................................................................................... 17

4.4 Tension de défaut supérieure à U ........................................................................ 17

4.5 Surtension............................................................................................................. 17

5 Marquage et instructions de fonctionnement ................................................................... 17

5.1 Marquage .............................................................................................................. 17

5.2 Instructions de fonctionnement .............................................................................. 17

6 Essais ........................................................................................................................... 18

6.1 Généralités ........................................................................................................... 18

6.2 Incertitude de fonctionnement ............................................................................... 18

6.3 Résistance externe ............................................................................................... 20

6.4 Tension de défaut ................................................................................................. 20

6.5 Surtension............................................................................................................. 20

Bibliographie ......................................................................................................................... 21

Tableau 1 – Calcul de l'incertitude de fonctionnement ............................................................ 19

---------------------- Page: 14 ----------------------
IEC 61557-3:2019 © IEC 2019 – 13 –
COMMISSION ÉLECTROTECHNIQUE INTERNATIONALE
____________
SÉCURITÉ ÉLECTRIQUE DANS LES RÉSEAUX DE DISTRIBUTION BASSE
TENSION AU PLUS ÉGALE À 1 000 V C.A. ET 1 500 V C.C. –
DISPOSITIFS DE CONTRÔLE, DE MESURE OU DE SURVEILLANCE
DE MESURES DE PROTECTION –
Partie 3: Impédance de boucle
AVANT-PROPOS
1) La Commission Electrotechnique Internationale
...

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