EN IEC 60076-25:2023

Power transformers - Part 25: Neutral grounding resistors

IEC 60076-25:2023 applies to dry type natural air-cooled resistors, for neutral grounding of transformers and generators, in order to limit the earth fault current in power systems by means of metallic resistive elements. For the purposes of this document, the resistor can be:  
used alone or in combination with other electrotechnical products not covered by this document, such as (but not limited to): a step-down single-phase transformer, an open triangle or zig-zag transformer (where the neutral point is not available) and a Petersen coil reactor (in order to increase active power contribution to the fault or reduce time constant for proper protection operation or both);
designed, manufactured and verified on a one-off basis or fully standardized and manufactured in quantity.  Both terms "neutral grounding resistor" (NGR) and "neutral earthing resistor" (NER) can be used. However, for the purposes of this document and in order to avoid any confusion with "neutral earthing reactor" (NER), the term "neutral grounding resistor" (NGR) is used. This document specifies:  
the characteristics of the NGR;
the service conditions requirements for NGRs;
the tests and test methods for confirming that these conditions have been met;
the requirements relating to marking for NGRs.  Annex A provides guidance on how to consider the effect of resistance variation with temperature.

Leistungstransformatoren - Teil 25: Sternpunkt-Erdungswiderstände

Transformateurs de puissance - Partie 25: Résistances de mise à la terre du neutre

L'IEC 60076-25:2023 s'applique aux résistances de type sec refroidies par air naturel pour la mise à la terre (MALT) du neutre des transformateurs et des générateurs dans le but de limiter le courant de défaut à la terre dans les réseaux d'énergie au moyen d'éléments résistifs métalliques. Pour les besoins du présent document, la résistance peut être:  
utilisée seule ou avec d'autres produits électrotechniques non couverts par le présent document, notamment: un transformateur abaisseur monophasé, un transformateur en triangle ouvert ou en zigzag (où le point neutre n'est pas disponible) et une bobine Petersen (afin d'augmenter la contribution de la puissance active au défaut et/ou de réduire la constante de temps pour améliorer la protection);
conçue, fabriquée et vérifiée à l'unité ou entièrement normalisée et fabriquée en quantité.  En anglais, les deux termes "neutral grounding resistor" (NGR) et "neutral earthing resistor" (NER) peuvent être utilisés pour désigner la résistance de mise à la terre du neutre (MALT). Toutefois, pour les besoins du présent document et afin d'éviter toute confusion avec la "réactance de mise à la terre du neutre" (NER, Neutral Earthing Reactor), le terme "neutral grounding resistor" (NGR) est utilisé. Le présent document spécifie:  
les caractéristiques de la MALT;
les exigences de conditions de service des MALT;
les essais et les méthodes d'essai pour confirmer que ces conditions ont été remplies;
les exigences relatives au marquage des MALT.  L'Annexe A fournit des recommandations pour prendre en compte l'impact de la température sur la variation de la résistance.

Močnostni transformatorji - 25. del: Upori za ozemljitev ničlišča (IEC 60076-25:2023)

Ta del standarda IEC 60076 se uporablja za naravno zračno hlajene suhe upore za ozemljitev ničlišča
transformatorjev in generatorjev za omejevanje toka zemeljskega stika v napajalnih sistemih z uporabo
kovinsko uporovnih elementov.
V tem dokumentu se lahko upor:
• uporablja samostojno ali v kombinaciji z drugimi elektrotehničnimi izdelki, ki niso zajeti v tem
dokumentu, kot so med drugim: enofazni transformator s transformacijo navzdol, odprti
transformator s trikotno ali cikcak vezavo (kjer nevtralna točka ni na voljo) in reaktor s
Petersenovo dušilko (za povečanje oddajanja delovne moči na stiku ali zmanjšanje časovne konstante
za ustrezno zaščito ali oboje);
• je lahko oblikovan, izdelan in preverjan enkratno ali je v celoti standardiziran in
proizveden v velikih količinah.
Uporabljata se lahko oba izraza »upor za ozemljitev ničlišča« (NGR) in »nevtralni ozemljitveni upor« (NER)
. Vseeno pa se v tem dokumentu zato, da ne bi prišlo do zamenjav z
»nevtralnim ozemljitvenim reaktorjem« (NER), uporablja izraz »upor za ozemljitev ničlišča« (NGR).
Ta dokument določa:
• značilnosti upora za ozemljitev ničlišča;
• zahteve za pogoje delovanja uporov za ozemljitev ničlišča;
• preskuse in preskusne metode za določanje, ali so ti pogoji izpolnjeni;
• zahteve v zvezi z označevanjem uporov za ozemljitev ničlišča.
Dodatek A vsebuje smernice o tem, kako upoštevati učinek spremembe upornosti s
temperaturo.

General Information

• Status: Published
• Publication Date: 30-Mar-2023
• ICS: 29.180 - Transformers. Reactors
• Technical Committee: CLC/TC 14 - Power transformers
• Drafting Committee: IEC/TC 14 - IEC_TC_14
• Current Stage: 6060 - Document made available - Publishing
• Start Date: 31-Mar-2023
• Completion Date: 31-Mar-2023
• Ref Project: SIST EN IEC 60076-25:2023 - Power transformers - Part 25: Neutral grounding resistors (IEC 60076-25:2023)

Standards Content (Sample)

SLOVENSKI STANDARD
01-junij-2023
Močnostni transformatorji - 25. del: Upori za ozemljitev ničlišča (IEC 60076-
25:2023)
Power transformers - Part 25: Neutral grounding resistors (IEC 60076-25:2023)
Leistungstransformatoren – Teil 25: Neutrale Erdungswiderstände (IEC 60076-25:2023)
Transformateurs de puissance - Partie 25: Résistances de mise à la terre du neutre (IEC
60076-25:2023)
Ta slovenski standard je istoveten z: EN IEC 60076-25:2023
ICS:
29.180 Transformatorji. Dušilke Transformers. Reactors
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 60076-25

NORME EUROPÉENNE
EUROPÄISCHE NORM March 2023
ICS 29.180
English Version
Power transformers - Part 25: Neutral grounding resistors
(IEC 60076-25:2023)
Transformateurs de puissance - Partie 25: Résistances de Leistungstransformatoren - Teil 25: Neutrale
mise à la terre du neutre Erdungswiderstände
(IEC 60076-25:2023) (IEC 60076-25:2023)
This European Standard was approved by CENELEC on 2023-03-30. 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,
Türkiye 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
© 2023 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 60076-25:2023 E

European foreword
The text of document 14/1097/FDIS, future edition 1 of IEC 60076-25, prepared by IEC/TC 14 "Power
transformers" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2023-12-30
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2026-03-30
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.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 60076-25:2023 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standard indicated:
IEC 60068-3-3 NOTE Approved as EN IEC 60068-3-3
IEC 60071-1 NOTE Approved as EN IEC 60071-1
IEC 60076-1 NOTE Approved as EN 60076-1
IEC 60664-1 NOTE Approved as EN IEC 60664-1
IEC 62271-1 NOTE Approved as EN 62271-1
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.cencenelec.eu.
Publication Year Title EN/HD Year
IEC 60060-1 2010 High-voltage test techniques - Part 1: General EN 60060-1 2010
definitions and test requirements
IEC 60071-2 - Insulation co-ordination - Part 2: Application EN IEC 60071-2 -
guidelines
IEC 60076-3 2013 Power transformers - Part 3: Insulation levels, EN 60076-3 2013
dielectric tests and external clearances in air
+ A1 2018 + A1 2018
IEC 60529 1989 Degrees of protection provided by enclosures EN 60529 1991
(IP Code)
- - + corrigendum May 1993
+ A1 1999 + A1 2000
+ A2 2013 + A2 2013
IEC 60076-25 ®
Edition 1.0 2023-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Power transformers –
Part 25: Neutral grounding resistors

Transformateurs de puissance –

Partie 25: Résistances de mise à la terre du neutre

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.180 ISBN 978-2-8322-6431-7

– 2 – IEC 60076-25:2023 © IEC 2023
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 7
4 Service conditions . 9
5 Ratings . 9
5.1 Rated ambient temperature . 9
5.2 Rated resistance (R) . 9
5.3 Maximum resistance variation . 9
5.4 Rated time . 9
5.5 Rated voltage (U ) . 9
r
5.6 Rated insulation level . 10
5.7 Rated short time current . 10
5.8 Rated continuous current . 10
5.9 Rated frequency . 10
6 Rating plates (Nameplates) . 11
6.1 General . 11
6.2 Minimum information to be provided . 11
7 Design and construction . 11
7.1 General . 11
7.2 Resistive elements . 11
7.3 Resistive banks. 12
7.4 Electrical connections . 12
7.5 IN and OUT terminals . 12
7.5.1 General . 12
7.5.2 IN terminal . 12
7.5.3 OUT terminal . 12
7.6 Insulators . 13
7.6.1 General . 13
7.6.2 Insulators between resistive elements . 13
7.6.3 Insulators between resistor banks and enclosure . 13
7.6.4 Creepage distance . 13
7.7 Enclosure . 13
7.7.1 Protection against contact with live parts, ingress of solid foreign bodies
and water . 13
7.7.2 Design . 13
7.7.3 Protection against corrosion . 14
8 Tests . 14
8.1 General . 14
8.2 Test classifications . 14
8.2.1 Routine tests . 14
8.2.2 Type tests . 14
8.2.3 Special tests . 15
8.3 Test documentation . 15
8.4 Routine tests. 15
8.4.1 Visual inspection and dimensional verification . 15

IEC 60076-25:2023 © IEC 2023 – 3 –
8.4.2 Rated resistance measurement. 15
8.4.3 Power frequency withstand voltage test . 15
8.4.4 Insulation resistance . 16
8.5 Temperature rise tests . 17
8.5.1 General . 17
8.5.2 Continuous current duty . 17
8.5.3 Rated time duty . 17
8.5.4 Tolerances . 18
8.5.5 Acceptance criteria . 18
8.6 Special tests . 18
8.6.1 Inductance measurement . 18
8.6.2 Lightning impulse test . 18
8.6.3 Mechanical design verification . 18
8.6.4 Protection degree of enclosure . 19
Annex A (informative) Resistance variation . 20
A.1 General . 20
A.2 Material properties . 20
A.3 Effect of NGR resistance variation . 20
A.4 Rate of variation . 21
A.5 Consecutive faults . 22
A.6 Protection coord
...