SIST EN 50708-3-3:2026

Power transformers - Additional European requirements: Part 3-3 Large power transformer - Accessories

This document describes the typical accessories used for Large Power Transformers.

Leistungstransformatoren – Zusätzliche europäische Anforderungen – Teil 3-3: Große Leistungstransformatoren

Transformateurs de puissance - Exigences européennes supplémentaires - Partie 3-3: Transformateurs de grande puissance - Accessoires

Le présent document décrit les accessoires types utilisés pour les transformateurs de grande puissance.

Močnostni transformatorji - Dodatne evropske zahteve - 3-3. del: Veliki močnostni transformator - Pribor

Ta dokument opisuje tipične dodatke, ki se uporabljajo za velike močnostne transformatorje.

General Information

• Status: Published
• Public Enquiry End Date: 14-Sep-2023
• Publication Date: 25-May-2026
• ICS: 29.180 - Transformers. Reactors
• Technical Committee: ETR - Power transformers
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 21-May-2026
• Due Date: 26-Jul-2026
• Completion Date: 26-May-2026
• Ref Project: EN 50708-3-3:2026 - Power transformers - Additional European requirements: Part 3-3: Large power transformer - Accessories

Relations

• Refers: SIST EN 60076-1:2012 - Power transformers - Part 1: General
• Effective Date: 19-May-2026
• Refers: SIST EN IEC 60076-22-1:2019 - Power transformers - Part 22-1: Power transformer and reactor fittings – Protective devices
• Effective Date: 19-May-2026
• Refers: SIST EN IEC 60076-22-6:2021 - Power transformers - Part 22-6: Power transformer and reactor cooling equipment - Fans
• Effective Date: 19-May-2026
• Refers: SIST EN IEC 60076-22-2:2019 - Power transformer and reactor cooling equipment - Part 22-2: Removable radiators
• Effective Date: 19-May-2026
• Refers: SIST EN 50708-1-2:2022 - Power transformers - Additional European requirements: Part 1-2 Common part - Assessment of energy performance
• Effective Date: 19-May-2026
• Refers: SIST EN IEC 60076-22-4:2019 - Power transformer and reactor cooling equipment - Part 22-4: Insulating liquid to water heat exchangers
• Effective Date: 19-May-2026
• Refers: SIST EN IEC 60076-22-5:2021 - Power transformers - Part 22-5: Power transformer and reactor fittings - Electric pumps for transformers
• Effective Date: 19-May-2026
• Refers: SIST EN IEC 60076-22-3:2019 - Power transformer and reactor cooling equipment - Part 22-3: Insulating liquid to air heat exchangers
• Effective Date: 19-May-2026
• Refers: SIST EN IEC 60076-22-8:2021 - Power transformers - Part 22-8: Power transformer and reactor fittings - Devices suitable for use in communication networks
• Effective Date: 19-May-2026
• Refers: SIST EN IEC 60076-22-7:2020 - Power transformers - Part 22-7: Power transformer and reactor fittings - Accessories and fittings
• Effective Date: 19-May-2026
• Refers: SIST EN 50708-1-1:2020 - Power transformers - Additional European requirements: Part 1-1: Common part - General requirements
• Effective Date: 19-May-2026
• Refers: SIST EN 13674-1:2011+A1:2017 - Railway applications - Track - Rail - Part 1: Vignole railway rails 46 kg/m and above
• Effective Date: 19-May-2026

Overview

SIST EN 50708-3-3:2026 defines the additional European requirements for accessories fitted to large power transformers. Developed by the Slovenian Institute for Standardization (SIST) as part of the EN 50708 series, this standard focuses on the typical mandatory and optional accessories required to ensure operational safety, reliability, and efficient maintenance of large power transformers. By harmonizing accessory requirements at the European level, the standard supports manufacturers, purchasers, and operators in specifying, designing, and assessing large power transformers intended for use in energy, utility, industrial, and infrastructure projects.

Key Topics

• Scope and Applicability

  • Addresses large power transformers categorized under European Standard EN 50708, specifically for units above 3,150 kVA.
  • Outlines typical accessories, their categories, and essential compliances.

• Accessory Requirements

  • Defines a comprehensive list of mandatory and optional accessories, including oil conservators, liquid level indicators, temperature indicators, protective relays, and cooling devices.
  • Sets requirements for compliance with relevant parts of EN IEC 60076-22 (Power transformer fittings).

• Special Requirements

  • Specific instructions and compliance for safety-critical accessories such as gas and liquid actuated relays (Buchholz relays), including the need for multi-stage alarm/trip functions and proper documentation.
  • Detailing of wheel assemblies for transformer movement with strict dimensional and material requirements for compatibility on standardized rail types.

• Reference and Terminology Alignment

  • Ensures harmonized terminology and service conditions as per EN 60076-1 and other referenced standards.
  • Provides cross-referencing for use with other parts of the EN 50708 and EN 60076 series.

Applications

SIST EN 50708-3-3:2026 serves as a critical reference for the following:

• Transformer Manufacturers

  • Guaranties consistency in the design and installation of essential and optional transformer accessories to meet European project specifications.
  • Facilitates standard-compliant tendering and manufacturing for large power transformers.

• Utilities and Network Operators

  • Ensures installed transformers are equipped with requisite accessories for monitoring, safety, and easy maintenance.
  • Reduces operational risks by standardizing controls such as temperature and liquid level monitors, relays, and safety valves.

• Procurement and Engineering Consultants

  • Provides a checklist of accessories and their specifications to include in procurement contracts and technical documentation.
  • Supports asset management by ensuring that transformers supplied across multiple projects adhere to harmonized European requirements.

• Maintenance and Service Providers

  • Offers clear expectations for accessories that aid in diagnostics, monitoring, and field servicing of large power transformers.

Related Standards

• EN 50708 Series: Power transformers - Additional European requirements

  • EN 50708-1-1: General requirements for power transformers
  • EN IEC 60076-22 Series: Power transformer and reactor fittings
  • EN 60076-1: Power transformers - General

• EN 13674-1: Railway applications - Rail
  For wheel compatibility and specifications if transformers are rail-transported.

• ISO and IEC Terminology Platforms

  • ISO Online Browsing Platform
  • IEC Electropedia

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By implementing the requirements set forth in SIST EN 50708-3-3:2026, stakeholders ensure that large power transformers throughout Europe are both safe and standardized, facilitating interoperability, safety, and performance across all major power and industrial sectors. This standard is essential for anyone involved in specifying, procuring, or operating large power transformers within the European market.

Standards Content (Sample)

SLOVENSKI STANDARD
01-julij-2026
Močnostni transformatorji - Dodatne evropske zahteve - 3-3. del: Veliki močnostni
transformator - Pribor
Power transformers - Additional European requirements: Part 3-3 Large power
transformer - Accessories
Leistungstransformatoren – Zusätzliche europäische Anforderungen – Teil 3-3: Große
Leistungstransformatoren
Transformateurs de puissance - Exigences européennes supplémentaires - Partie 3-3:
Transformateurs de grande puissance - Accessoires
Ta slovenski standard je istoveten z: EN 50708-3-3:2026
ICS:
29.180 Transformatorji. Dušilke Transformers. Reactors
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN 50708-3-3

NORME EUROPÉENNE
EUROPÄISCHE NORM May 2026
ICS 29.180
English Version
Power transformers - Additional European requirements: Part 3-
3: Large power transformer - Accessories
Transformateurs de puissance - Exigences européennes Leistungstransformatoren - Zusätzliche europäische
supplémentaires - Partie 3-3: Transformateurs de grande Anforderungen - Teil 3-3: Große Leistungstransformatoren
puissance - Accessoires
This European Standard was approved by CENELEC on 2026-03-23. 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
© 2026 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 50708-3-3:2026 E
Contents Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Service conditions . 5
5 Main accessories . 5
6 Specific requirements for certain accessories. 7
6.1 Gas and liquid actuated relay (Buchholz relays) . 7
6.2 Specific requirement for wheels. 8

European foreword
This document (EN 50708-3-3:2026) has been prepared by CLC/TC 14 “Power transformers”.
The following dates are fixed:
— latest date by which this document has to be (dop) 2027-05-31
implemented at national level by publication of
an identical national standard or by
endorsement
— latest date by which the national standards (dow) 2029-05-31
conflicting with this 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.
Introduction
This part is a part of EN 50708 series that deals with the accessories for large power transformers.
For the purpose of this document, the requirements of the general EN 50708-1-1:2020 apply.
This document contains particular requirements for specific transformers or transformer applications, which are
based on the requirements of the general EN 50708-1-1:2020.
This document should be considered in conjunction with the requirements of the general parts.
The particular requirements of the different sub parts of the EN 50708 series supplement, modify or replace
certain requirements of the general parts of EN 50708-1 and/or EN 50708-1-X being valid at the time of
publication of this document. The absence of references to the exclusion of a part or a clause of a general part
means that the corresponding clauses of the general part are applicable (undated reference).
Requirements of other -X parts with X greater than 1 being eventually relevant for cases covered by this
document also apply. This document could therefore also supplement, modify or replace certain of these
requirements valid at the time of publication of this document.
The main clause numbering of each part follows the pattern and corresponding references of EN 50708-1-
1:2020. The numbers following the particular number of this document are those of the corresponding parts, or
clauses of the other parts of the EN 50708 series, valid at the time of publication of this document.
In the case where new or amended general parts with modified numbering were published after the sub part
was issued, the clause numbers referring to a general part in sub parts might no longer align with the latest
edition of the general part. Dated references should be observed.
1 Scope
This document describes the typical accessories used for Large Power Transformers.
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 13674-1, Railway applications — Track — Rail — Part 1: Vignole railway rails 46 kg/m and above
EN 50708 (all parts), Power transformers — Additional European requirements
EN 60076-1, Power transformers — Part 1: General (IEC 60076-1)
EN IEC 60076-22 (all parts), Power transfor
...