oSIST prEN 50522:2021

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

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

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

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

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,

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

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

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

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

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

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

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:

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

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

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

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

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

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

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

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

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

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

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

— 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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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