oSIST prEN 50522:2021

Earthing of power installations exceeding 1 kV a.c.

Revision of the existing EN 50522 to complement the EN 61936 with European earthing system design requirements

Erdung von Starkstromanlagen mit Nennwechselspannungen über 1 kV

Prises de terre des installations électriques en courant alternatif de puissance supérieure à 1 kV

Le présent document a pour objectif de spécifier les exigences relatives à la conception et la mise en œuvre des installations de mise à la terre des installations électriques, dans des réseaux où la tension nominale est supérieure à 1 kV en courant alternatif et pour une fréquence nominale jusqu’à 60 Hz inclus, afin d'assurer la sécurité et le fonctionnement correct dans le cadre de l'utilisation prévue. NOTE 1 Les principes techniques et de procédure du présent document peuvent être appliqués lorsque des installations et des équipements de tiers sont prévus et/ou construits à proximité d'installations électriques à haute tension. Pour l’interprétation du présent document, une installation électrique est considérée comme étant l'une des suivantes: a) poste, y compris les postes d’alimentation de ligne ferroviaire; b) installations électriques sur mât, pylône et tour; appareillage et/ou transformateurs situés à l'extérieur d'une installation électrique fermée; c) une ou plusieurs centrales électriques placées dans un site unique; l'installation électrique comprend les générateurs et les transformateurs avec tout l'appareillage et tous les auxiliaires électriques associés. Les liaisons entre les postes faisant partie du réseau de transmission ou de distribution sont cependant exclues; d) le système électrique d’une usine, d’un site industriel ou d’autres installations industrielles, agricoles, commerciales ou publiques; e) les installations électriques en pleine mer à des fins de production, de transport, de distribution et/ou de stockage d'électricité; f) les tours/pylônes de transition entre les lignes aériennes et les lignes souterraines. L'installation électrique comprend notamment les matériels suivants: — machines électriques tournantes; — appareillage; — transformateurs et réactances; — convertisseurs; — câbles; — canalisations électriques; — batteries; — condensateurs; — installations de mise à la terre; — bâtiments et clôtures qui font partie intégrante d'une installation électrique fermée; — les systèmes associés de protection, de commande et auxiliaires; — réactance élevée à noyau d’air. NOTE 2 Généralement, une norme traitant d'un équipement particulier prévaut sur le présent document. Le présent document ne s'applique pas à la conception et la mise en œuvre des installations de mise à la terre des installations suivantes: — lignes aériennes et souterraines entre des installations différentes; NOTE 3 La série de normes EN 50341 Lignes électriques aériennes dépassant 1 kV en courant alternatif, spécifie les exigences relatives à la conception et la mise en œuvre des installations de mise à la terre des lignes aériennes. — voies ferrées et matériel roulant électrifiés; — matériels et installations de mine; — installations d’éclairages fluorescents; — installations sur les bateaux et plates-formes en mer; — matériels électrostatiques (par exemple, précipiteurs électrostatiques, cabines de peinture); — stations d'essai; — matériel médical, par exemple, équipement à rayons X. NOTE 4 Les exigences relatives aux travaux effectués sous tension sur des installations électriques ne relèvent pas du domaine d'application du présent document. NOTE 5 Le domaine d'application du présent document inclut les exigences de sécurité pour les installations HT et ses influences sur les installations BT. Pour les installations électriques jusqu'à 1 kV, la série de normes IEC 60364 s'applique.

Ozemljitev elektroenergetskih postrojev, ki presegajo 1 kV izmenične napetosti

General Information

• Status: Not Published
• Public Enquiry End Date: 31-May-2021
• ICS: 29.120.50 - Fuses and other overcurrent protection devices
• ICS: 29.240.01 - Power transmission and distribution networks in general
• Technical Committee: IVNI - High voltage power installations
• Current Stage: 4020 - Public enquire (PE) (Adopted Project)
• Start Date: 22-Apr-2020
• Due Date: 09-Sep-2020
• Completion Date: 16-Jul-2021
• Ref Project: prEN 50522 - Earthing of power installations exceeding 1 kV a.c.

RELATIONS

• Revised: SIST EN 50522:2011 - Earthing of power installations exceeding 1 kV a.c.
• Effective Date: 13-Feb-2018

Standards Content (sample)

SLOVENSKI STANDARD
oSIST prEN 50522:2021
01-maj-2021
Ozemljitev elektroenergetskih postrojev, ki presegajo 1 kV izmenične napetosti
Earthing of power installations exceeding 1 kV a.c.
Erdung von Starkstromanlagen mit Nennwechselspannungen über 1 kV

Prises de terre des installations électriques en courant alternatif de puissance supérieure

à 1 kV
Ta slovenski standard je istoveten z: prEN 50522
ICS:
29.240.01 Omrežja za prenos in Power transmission and
distribucijo električne energije distribution networks in
na splošno general
oSIST prEN 50522:2021 en

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

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oSIST prEN 50522:2021
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oSIST prEN 50522:2021
EUROPEAN STANDARD DRAFT
prEN 50522
NORME EUROPÉENNE
EUROPÄISCHE NORM
March 2021
ICS 29.120.50 Will supersede EN 50522:2010 and all of its
amendments and corrigenda (if any)
English Version
Earthing of power installations exceeding 1 kV a.c.

Prises de terre des installations électriques en courant Erdung von Starkstromanlagen mit

alternatif de puissance supérieure à 1 kV Nennwechselspannungen über 1 kV
This draft European Standard is submitted to CENELEC members for enquiry.
Deadline for CENELEC: 2021-06-11.
It has been drawn up by CLC/TC 99X.

If this draft becomes a European Standard, 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.

This draft European Standard was established by CENELEC 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.

Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are aware and to

provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without notice and

shall not be referred to as a European Standard.
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

© 2021 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.

Project: 66575 Ref. No. prEN 50522 E
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prEN 50522:2021 (E)
Contents Page

European foreword ............................................................................................................................................ 4

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

2 Normative references ........................................................................................................................... 6

3 Terms and definitions .......................................................................................................................... 7

4 Fundamental requirements ................................................................................................................ 14

4.1 General requirements ......................................................................................................................... 14

4.2 Electrical requirements ...................................................................................................................... 14

4.2.1 Methods of neutral earthing .............................................................................................................. 14

4.2.2 Short-circuit current ........................................................................................................................... 14

4.3 Safety criteria ...................................................................................................................................... 14

4.4 Functional requirements .................................................................................................................... 15

5 Design of earthing systems ............................................................................................................... 15

5.1 General ................................................................................................................................................. 15

5.2 Dimensioning with respect to corrosion and mechanical strength .............................................. 15

5.2.1 Earth electrodes .................................................................................................................................. 15

5.2.2 Earthing conductors ........................................................................................................................... 15

5.2.3 Bonding conductors ........................................................................................................................... 15

5.3 Dimensioning with respect to thermal strength .............................................................................. 16

5.3.1 General ................................................................................................................................................. 16

5.3.2 Current rating calculation .................................................................................................................. 16

5.4 Dimensioning with regard to touch voltages ................................................................................... 18

5.4.1 Permissible values ............................................................................................................................. 18

5.4.2 Measures for the observance of permissible touch voltages ........................................................ 19

5.4.3 Design procedure ............................................................................................................................... 19

6 Measures to avoid transferred potential .......................................................................................... 22

6.1 Transferred potential from high voltage systems to low voltage systems .................................. 22

6.1.1 High and low voltage earthing systems ........................................................................................... 22

6.1.2 LV supply only within HV substations ............................................................................................. 22

6.1.3 LV supply leaving or coming to HV substations ............................................................................. 22

6.1.4 LV in the proximity of HV substation ................................................................................................ 22

6.2 Transferred potentials to telecommunication and other systems ................................................ 23

7 Construction of earthing systems .................................................................................................... 23

7.1 Installation of earth electrodes and earthing conductors .............................................................. 23

7.2 Lightning and transients .................................................................................................................... 24

7.3 Measures for earthing on equipment and installations .................................................................. 24

8 Measurements ..................................................................................................................................... 24

9 Maintainability ..................................................................................................................................... 24

9.1 Inspections .......................................................................................................................................... 24

9.2 Measurements ..................................................................................................................................... 24

10 Inspection and documentation of earthing systems ...................................................................... 24

Annex A (normative) Methods of calculating permissible touch voltages ............................................... 25

Annex B (normative) Calculation of Permissible touch voltage U , Prospective permissible touch

voltage U ....................................................................................................................................... 28

vTp

Annex C (normative) Type and minimum dimensions of earth electrode materials ensuring mechanical

strength and corrosion resistance ................................................................................................... 33

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Annex D (normative) Current rating calculation of earthing conductors and earth electrodes .... 35

Annex E (normative) Description of the recognized specified measures M .................................... 40

Annex F (normative) Measures on earthing systems to reduce the effects of high frequency

interference ................................................................................................................................. 43

Annex G (normative) Detailed measures for earthing of equipment and installations ................... 44

Annex H (normative) Measuring touch voltages ................................................................................. 47

Annex I (informative) Reduction factors related to earth wires of overhead lines and metal sheaths

of underground cables............................................................................................................... 48

Annex J (informative) Basis for the design of earthing systems ...................................................... 51

Annex K (informative) Installing the earth electrodes and earthing conductors ............................ 55

Annex L (informative) Measurements for and on earthing systems ................................................. 57

Annex M (informative) The use of reinforcing bars in concrete for earthing purpose ................... 67

Annex N (informative) Global Earthing System .................................................................................. 68

Annex O (normative) Special national conditions .............................................................................. 69

Annex P (informative) A-deviations ...................................................................................................... 70

Bibliography ............................................................................................................................................. 72

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European foreword

This document (prEN 50522:2021) has been prepared by CLC/TC 99X “Power installations exceeding 1 kV a.c.

(1,5 kV d.c.)”.
This document is currently submitted to the Enquiry.
The following dates are proposed:
• latest date by which the existence of this (doa) dor + 6 months
document has to be announced at national
level
• latest date by which this document has to be (dop) dor + 12 months
implemented at national level by publication of
an identical national standard or by
endorsement
• latest date by which the national standards (dow) dor + 36 months
conflicting with this document have to be (to be confirmed or
withdrawn modified when voting)

This document will supersede EN 50522:2010 and all of its amendments and corrigenda (if any).

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oSIST prEN 50522:2021
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1 Scope

This document is applicable to specify the requirements for the design and erection of earthing systems of

electrical installations, in systems with nominal voltage above 1 kV AC and nominal frequency up to and

including 60 Hz, so as to provide safety and proper functioning for the use intended.

NOTE 1 The technical and procedural principles of this document can be applied when 3rd parties’ installations and

facilities are planned and/or erected in the vicinity of HV electrical power installations.

For the purpose of interpreting this document, an electrical power installation is considered to be one of the

following:
a) substation, including substation for railway power supply;
b) electrical power installations on mast, pole and tower;

switchgear and/or transformers located outside a closed electrical operating area;

c) one (or more) power station(s) located on a single site;

the electrical power installation includes generators and transformers with all associated switchgear and all

electrical auxiliary systems. Connections between generating stations located on different sites are

excluded;

d) the electrical system of a factory, industrial plant or other industrial, agricultural, commercial or public

premises;

e) electrical power installations on offshore facilities for the purpose of generation, transmission, distribution

and/or storage of electricity;
f) transition towers/poles between overhead lines and underground lines.

The electrical power installation includes, among others, the following equipment:

— rotating electrical machines;
— switchgear;
— transformers and reactors;
— converters;
— cables;
— wiring systems;
— batteries;
— capacitors;
— earthing systems;
— buildings and fences which are part of a closed electrical operating area;
— associated protection, control and auxiliary systems;
— large air core reactor.

NOTE 2 In general, a standard for an item of equipment takes precedence over this document.

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This document does not apply to the design and erection of earthing systems of any of the following:

— overhead and underground lines between separate installations;

NOTE 3 The standard, EN 50341 series Overhead lines exceeding AC 1 kV, specifies requirements for the design and

erection of earthing systems in overhead lines.
— electrified railway tracks and rolling stock;
— mining equipment and installations;
— fluorescent lamp installations;
— installations on ships and off-shore installations;

— electrostatic equipment (e.g. electrostatic precipitators, spray-painting units);

— test sites;
— medical equipment, e.g. medical X-ray equipment.

NOTE 4 The scope of this document does not include the requirements for carrying out live working on electrical power

installations.

NOTE 5 The scope of this document considers safety requirements for HV installations and its influences on LV

installations. For electrical installation up to 1 kV, the standard IEC 60364 series applies.

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.

EN 60909 (series), Short-circuit currents in three-phase a.c. systems (IEC 60909 series)

EN 60909-3:2010, Short-circuit currents in three-phase a.c systems - Part 3: Currents during two separate

simultaneous line-to-earth short-circuits and partial short-circuit currents flowing through earth

(IEC 60909-3:2009)

EN IEC 62561-2, Lightning protection system components (LPSC) - Part 2: Requirements for conductors and

earth electrodes (IEC 62561-2)

HD 60364-1, Low-voltage electrical installations - Part 1: Fundamental principles, assessment of general

characteristics, definitions (IEC 60364-1)

IEC 60479-1:2018, Effects of current on human beings and livestock – Part 1: General aspects

IEC 61936-1:2010, Power installations exceeding 1 kV a.c. - Part 1: Common rules
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3 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC 61936-1:2010 and the following 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/
3.1
earth ring electrode
earth electrode embedded in the soil around a building or pole as a closed ring
3.2
effective touch voltage
touch voltage
voltage between conductive parts when touched simultaneously

Note 1 to entry: The value of the effective touch voltage could be appreciably influenced by the impedance of the person

in electric contact with these conductive parts.
Note 2 to entry: The person is touching the conductive parts with bare skin.
[SOURCE: IEC 60050-195:1998, 195-05-11, modified]
[SOURCE: IEC 61936-1:2010, 3.7.4, modified – note 2 added]
3.3
permissible touch voltage
limit value of touch voltage U
Note 1 to entry: See Figure 8.
3.4
prospective touch voltage

voltage between simultaneously accessible conductive parts when those conductive parts are not being touched

Note 1 to entry: See Figure 1.
[SOURCE: IEC 60050-195:1998, 195-05-09, modified]
[SOURCE: IEC 61936-1:2010, 3.7.15, modified – note added]
3.5
prospective permissible touch voltage
vTp
limit value of prospective touch voltage U
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3.6
transferred potential

potential rise of an earthing system caused by a current to earth transferred by means of a connected conductor

(for example a metallic cable sheath, PEN conductor, pipeline, rail) into areas with low or no potential rise

relative to reference earth, resulting in a potential difference occurring between the conductor and its

surroundings
Note 1 to entry: See Figure 1.
[SOURCE: IEC 61936-1:2010, 3.7.17, modified – reference Figure 1 added]
3.7
global earthing system

equivalent earthing system created by the interconnection of local earthing systems that ensures, by the

proximity of the earthing systems, that there are no touch voltages exceeding permissible limit values

Note 1 for entry: Such systems permit the division of the earth fault current in a way that results in a reduction of the earth

potential rise at the local earthing system. Such a system could be said to form a quasi equipotential surface.

Note 2 for entry: The existence of a global earthing system may be determined by sample measurements or calculation for

typical systems. Typical examples of global earthing systems are in city centres; urban or industrial areas with distributed

low- and high-voltage earthing (see Annex N).
[SOURCE: IEC 61936-1:2010, 3.7.19, modified – note 2 reference to Annex added]
3.8
system with isolated neutral

system in which the neutrals of transformers and generators are not intentionally connected to earth, except for

high impedance connections for signalling, measuring or protection purposes
[SOURCE: IEV 601-02-24, modified]
3.9
system with resonant earthing

system in which at least one neutral of a transformer or earthing transformer is earthed via an arc suppression

coil and the combined inductance of all arc suppression coils is essentially tuned to the earth capacitance of the

system for the operating frequency

Note 1 for entry: In case of no self-extinguishing arc fault there are two different operation methods used:

— automatic disconnection;
— continuous operation during fault localization process.

In order to facilitate the fault localization and operation there are different supporting procedures:

— short term earthing for detection;
— short term earthing for tripping;
— operation measures, such as disconnection of coupled busbars;
— phase earthing.

Note 2 for entry: Arc suppression coil may have high ohmic resistor in parallel to facilitate fault detection.

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3.10
system with low-impedance neutral earthing

system in which at least one neutral of a transformer, earthing transformer or generator is earthed directly or

via an impedance designed such that due to an earth fault at any location the magnitude of the fault current

leads to a reliable automatic tripping due to the magnitude of the fault current
[SOURCE: IEV 601-02-25, 601-02-26]
3.11
earth fault current

current which flows from the main circuit to earth or earthed parts at the fault location (earth fault location)

Note 1 to entry: See Figures 2 to 7.
Note 2 for entry: For single earth faults, this is:
— in systems with isolated neutral, the capacitive earth fault current,
— in systems with high resistive earthing, the RC composed earth fault current,
— in systems with resonant earthing, the earth fault residual current,

— in systems with solid or low impedance neutral earthing, the line-to-earth short-circuit current.

Note 3 for entry: Further earth fault current could result from double earth fault and line to line to earth.

[SOURCE: IEC 61936-1:2010, 3.7.25, modified – reference to Figures added]
3.12
current to earth
current flowing to earth via the impedance to earth
Note 1 for entry: See Figure 2.

Note 2 for entry: The current to earth is the part of the earth fault current I , which causes the potential rise of the earthing

system. For the determination of I see also Annex L.
3.13
reduction factor

factor r of a three phase line is the ratio of the current to earth over the sum of the zero sequence currents in

the phase conductors of the main circuit (r = I / 3 I ) at a point remote from the short-circuit location and the

E 0
earthing system of an installation
3.14
horizontal earth electrode

electrode which is generally buried at a depth of up to approximately 1 m. It can consist of strip, round bar or

stranded conductor and can be laid out to form a radial, ring or mesh earth electrode or a combination of these

3.15
cable with earth electrode effect

cable whose sheaths, screens or armourings have the same effect as a horizontal electrode consisting of bare

round earth-wire
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3.16
foundation earth electrode

conductive structural embedded in concrete which is in conductive contact with the earth via a large surface

[SOURCE: IEV 826-13-08, modified]
3.17
potential grading earth electrode

conductor which due to shape and arrangement is principally used for potential grading rather than for

establishing a certain resistance to earth
Key
E Earth electrode

S1, S2, S3 Potential grading earth electrodes (e.g. ring earth electrodes), connected to the earth electrode E

Earth potential rise
Prospective step voltage
Prospective touch voltage

A Prospective touch voltage resulting from transferred potential in case of single side cable sheath earthing

B Prospective touch voltage resulting from transferred potential in case of cable sheath earthed on both sides

φ Earth surface potential

Figure 1 — Example for the surface potential profile and for the voltages in case of current carrying

earth electrodes
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Key
3 I
Three times zero sequence current of the line
Current via neutral earthing of the transformer
Earth fault current
Current to earth (cannot be measured directly)
Current via the resistance to earth of the mesh earth electrode
Reduction factor of the overhead line
R , R
Resistance to earth of the mesh earth electrode
ES ESx
Resistance to earth of the tower

Chain impedance (several number of towers with resistance to earth, R ) represents a value of the

overhead line assumed to be infinite
Impedance to earth
U Earth potential rise
n Number of overhead lines leaving the substation (here: n = 2)

Figure 2 — Example for currents, voltages and resistances for an earth fault in a transformer

substation with low impedance neutral earthing
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Key
Earth fault current
Capacitive earth fault current (complex value, including ohmic component)
I may include ohmic component.
Figure 3 — Earth fault current in a system with isolated neutral
Key
Earth fault current
Capacitive earth fault current (complex value, including ohmic component)

Sum of the currents of the parallel arc-suppression coils (complex value, including ohmic component)

Harmonic current (different frequencies)
Earth fault residual current
RES
NOTE I is the ohmic part of the complex value of (I + I ).
R C L
Figure 4 — Earth fault current in a system with resonant earthing
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Key
Earth fault current
Initial symmetrical short-circuit current for a line-to-earth short circuit
If I is in the same order as I” this current has to be considered additionally.
C k1
Figure 5 — Earth fault current in a system with low impedance neutral earthing
Key
Earth fault current
Earth fault residual current
RES
Initial symmetrical short-circuit current for a line-to-earth short circuit

Figure 6 — Earth fault current in a system with resonant earthing and temporary low impedance

neutral earthing
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Key
Earth fault current
Double earth fault current
kEE

Figure 7 — Double earth fault current in a system with isolated neutral or resonant earthing

4 Fundamental requirements
4.1 General requirements

This document provides the criteria for design, installation, testing and maintenance of an earthing system such

that it operates under all conditions and ensures the safety of human life in any place to which persons have

legitimate access. It also provides the criteria to ensure that the integrity of equipment connected and in

proximity to the earthing system is maintained.
The requirements of IEC 61936-1:2010, 4.1.1 first and second paragraph apply.
4.2 Electrical requirements
4.2.1 Methods of neutral earthing
The requirements of IEC 61936-1:2010, 4.2.1 apply.
4.2.2 Short-circuit current

The requirements of IEC 61936-1:2010, 4.2.4 paragraph 1, 2, 3, 4, 5 and NOTE 1 apply.

The rated duration should be determined taking into consideration the fault clearance time described in

IEV 448-13-15.
4.3 Safety criteria
The requirements of IEC 61936-1:2010, 10.2.1 paragraph 1 and 2 apply.

For installation design, the curve shown in Figure 8 is calculated according to the method defined in Annex A

and Annex B.
The requirements of IEC 61936-1:2010, 10.2.1 NOTE apply.
The curve in Figure 8, which gives the permissible touch voltage, shall be used.
The requirements of IEC 61936-1:2010, 10.2.1 paragraph 5 apply.
See A.3
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For installations where high voltage equipment is not located in closed electrical operating areas, e.g. in an

industrial environment, a global earthing system should be applied to prevent touch voltages exceeding

permissible limit values.
4.4 Functional requirements
The requirements of IEC 61936-1:2010, 10.2.2 paragraph 1,2,3 and 4 apply.

NOTE The requirement to keep step and touch voltages within permissible levels does not apply to temporary earth

connections (portable earthing equipment) at work locations.
The requirements of IEC 61936-1:2010, 10.2.2 paragraph 5 apply.
5 Design of earthing systems
5.1 General
Parameters relevant to earthing system dimensioning are:
— value of fault current;
— fault duration;
— soil characteristics.

NOTE The value of fault current and fault duration mainly depend on the method of neutral earthing of the high voltage

system.
5.2 Dimensioning with respect to corrosion and mechanical strength
5.2.1 Earth electrodes

The electrodes, being directly in contact with the soil, shall be of materials capable of withstanding corrosion

(chemical or biological attack, oxidation, formation of an electrolytic couple, electrolysis, etc.). They have to

resist the mechanical influences during their installation as well as those occurring during normal service. It is

acceptable to use steel embedded in concrete foundations and steel piles or other natural earth electrodes as

a part of the earthing system. Mechanical strength and corrosion considerations dictate the minimum

dimensions
...