CLC/TC 14 - Power transformers

IEC 60076-19-1:2023 defines the procedures that are applied to evaluate the uncertainty affecting the measurements of no-load and load losses during the routine tests on power transformers. This document centres on measuring systems utilizing digital instruments, although the procedures can be adapted to evaluation of systems with analogue instruments where further uncertainty sources have to be taken into account. This document specifies how to determine measurement uncertainty and how to apply corrections for known errors in the measurement chain. Information vis-à-vis judgement and traceability are given in IEC 60076-8:1997, 10.1 and 10.2.

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.

This document describes a special test for tanks of liquid-immersed transformers which during service are hermetically sealed and fully filled with liquid and volume change of the liquid due to temperature change compensated by elastic deformation of the cooling element for Large Power Transformers having a rated power greater than 3150 kVA.

This document describes the list of typical accessories used for liquid and dry type Medium Power Transformers (≤ 3 150 kVA).

This document defines the energy performance of non-conventional technology Medium Power Transformers in compliance with EN 50708-1-1.

This document describes the special tests for Medium Power Transformers ≤ 3150 kVA compliant with the EN 50708 2 series: - for corrugated tank for liquid immersed transformers, - for the method of measurement of losses for one winding in Highest Voltage (HV) and windings in Lowest Voltage (LV) for liquid immersed and dry type transformers.

IEC 60076-22-2:2019 applies to radiators mounted on liquid immersed power transformers according to IEC 60076-1 and reactors according to IEC 60076-6 with and without conservator for indoor or outdoor installation. It outlines the service conditions and the mechanical and electrical requirements that are common to this equipment. It also outlines the operation requirements specific to this equipment as well as the preferred dimensions relevant for interchangeability and the type and routine tests to be performed. Keywords: radiators mounted on liquid immersed power transformers

This part of IEC 60076 applies to liquid to air heat exchangers, using forced air and forced liquid circuits, used on liquid immersed power transformers according to IEC 60076-1 and reactors according to IEC 60076-6 with and without conservator for indoor or outdoor installation. It outlines the service conditions and the mechanical and electrical requirements that are common to this equipment. It also outlines the operation requirements specific to this equipment as well as the preferred dimensions relevant for interchangeability and the type and routine tests to be performed.

This part of IEC 60076 applies to liquid to water heat exchangers, using forced water and forced liquid circuits, used on liquid immersed power transformers according to IEC 60076-1 and reactors according to IEC 60076-6 with and without conservator for indoor or outdoor installation. It outlines the service conditions and the mechanical and electrical requirements that are common to this equipment. It also outlines the operation requirements specific to this equipment as well as the preferred dimensions relevant for interchangeability and the type and routine tests to be performed.

IEC 60076-22-1:2019 applies to protective devices mounted on liquid-immersed power transformers in accordance with IEC 60076-1 and reactors in accordance with IEC 60076-6 with or without conservator for indoor or outdoor installation. It outlines the service conditions and the mechanical and electrical requirements that are common to all the devices, which are relevant for the safety of the machine having a function of signalization of abnormal operating conditions. It also outlines the operation requirements specific to each device as well as, in some cases, the preferred dimensions relevant for interchangeability and the type and routine test to be performed. Keywords: protective devices mounted on liquid-immersed power transformers

This document applies to all power transformers in scope of TC 14.

NEW!IEC 60076-11:2018 is available as IEC 60076-11:2018 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.IEC 60076-11:2018 applies to dry-type power transformers (including auto-transformers) having values of highest voltage for equipment up to and including 72,5 kV and at least one winding operating at greater than 1,1 kV. This document does not apply to: - gas-filled dry-type transformers where the gas is not air; - single-phase transformers rated at less than 5 kVA; - polyphase transformers rated at less than 15 kVA; - instrument transformers; - starting transformers; - testing transformers; - traction transformers mounted on rolling stock; - flameproof and mining transformers; - welding transformers; - voltage regulating transformers; - small power transformers in which safety is a special consideration. Where IEC standards do not exist for the transformers mentioned above or for other special transformers, this document may be applicable as a whole or in parts. This second edition cancels and replaces the first edition published in 2004 and constitutes a technical revision. The main changes with regard to the previous edition are as follows: - Extension of the scope up to 72,5kV - Enclosure management in regards of the performance - Management of the dielectric and thermal features with altitude - New climatic classes for a better adaptation of customers’ need - Establishment of the relation between location and environmental classes - For fire behaviour classes, limitation at 1000kVA and process of test more robust - Introduction of Seismic class - Recommendations for amorphous transformers Keywords: dry-type transformers

The scope of this document is to define the energy performance of liquid immersed single-phase Medium Power Transformers in compliance with EN 50708 1 1:2020.

This part of IEC 60076-22 applies to a selection of accessories and fittings mounted on liquid immersed power transformers according to IEC 60076-1 and reactors according to IEC 60076-6 with or without conservator for indoor or outdoor installation. It outlines the operation requirements specific to each device as well as the data made available to the communication network and the type and routine test to be performed. The communication network is not part of the scope of this standard.

IEC 60076-22-6:2021 covers the electric fans used in the cooling circuits of power transformers and reactors. It applies to electric fans mounted on liquid immersed power transformers according to IEC 60076-1 and reactors according to IEC 60076-6 with and without conservator for indoor or outdoor installation. It outlines the service conditions and the mechanical and electrical requirements that are common to all the equipment. The electric fans concerned by this document are of the axially operating type and are for use on liquid to air coolers and for blowing out radiators. This document also outlines the operation requirements specific to each equipment as well as the preferred dimensions relevant for interchangeability and uniform fan assembly and the type and routine tests to be performed.

IEC 60076-22-5:2021 covers electric pumps used in the cooling circuits of power transformers and reactors. It applies to electric pumps mounted on liquid immersed power transformers according to IEC 60076-1 and reactors according to IEC 60076-6 with and without conservator for indoor or outdoor installation. It outlines the operation requirements for the electrical and hydraulic performance, mechanical design, routine testing and type testing. Additionally, performance and dimensions of preferred sizes of pump sets are specified in informative annexes. The pumps covered in this document are rotodynamic pumps driven by a squirrel cage induction motor that is immersed in the insulating liquid. Pump sets conforming to this document can be of in-line or end suction design.

TC - Correction of technical errors

TC - Correction of technical errors

IEC 60076-24:2020 applies to medium power transformers from 25 kVA up to 3 150 kVA with highest voltage for equipment up to 36 kV, or in low voltage (LV) networks with highest voltage for equipment of up to 1,1 kV equipped with voltage regulating devices. Voltage regulating distribution transformers are transformers equipped with components to control primary or secondary voltage for on-load voltage regulation purposes. The main objective of the installation of a VRDT is to regulate the LV network voltage level (i.e. 400 V), to avoid violation of the limits defined by relevant standards or regulations. The VRDT must operate properly as a step down and step up transformer. Transformers covered by this document comply with the relevant requirements set out in IEC 60076 (all parts) and, unless otherwise stated in this document, they also comply with European Standards EN 50160 and EN 50588-1.

IEC 60076-22-7:2020 applies to a selection of accessories and fittings mounted on liquid immersed power transformers according to IEC 60076-1 and reactors according to IEC 60076­6 with or without conservator for indoor or outdoor installation. It outlines the service conditions and the mechanical requirements that are common to all the accessories and fittings. This document also outlines the operation requirements specific to each device as well as the preferred dimensions relevant for interchangeability and the type and routine test to be performed.This document covers an exhaustive selection of the accessories and fittings that are currently used on transformers or reactors.

The scope of this document is to define the energy performance of Medium Power Transformers in compliance with EN 50708-1-1:2020.

The scope of this document is to define performance requirements of Large Power Transformers in compliance with EN 50708-1-1:2020. NOTE This document covers the transformers under Commission Regulation (EU) No 548/2014 of 21 May 2014 and its amendment No 2019/1783 of 1 October 2019, gives additional specific guidance for single phase transformers, autotransformers, multi winding transformers and for transformers with OD and OF cooling systems, necessary for the correct application of energy efficiency requirements to these categories of transformers.

This document is part of the EN 50708 series which applies to transformers in compliance with EN 60076-1.

IEC 60076-10:2016 defines sound pressure and sound intensity measurement methods from which sound power levels of transformers, reactors and their associated cooling devices are determined. The methods are applicable to transformers, reactors and their cooling devices - either fitted to or separate from the transformer - as covered by the IEC 60076 and IEC 61378 series. This standard is primarily intended to apply to measurements made at the factory. Conditions on-site can be very different because of the proximity of objects, including other transformers. Nevertheless, this standard is applied to the extent possible for on site measurements. This edition includes the following significant technical changes with respect to the previous edition: - additional useful definitions introduced; - definition of distribution type transformers introduced for the purpose this standard; - new clause for sound level measurement specification introduced; - requirement for 1/3 octave band measurements introduced for transformers other than distribution type transformers; - standard measurement distance changed from 0,3 m to 1 m for transformers other than distribution type transformers; - height of measurement surface is now clearly defined to count from the reflecting plane; - measurement surface formula unified; - correction criteria for intensity method introduced; - rules for sound measurements on dry-type reactors introduced; - figures revised; - new informative test report templates introduced (Annex B); - IEC 60076-10-1 (application guide) revised in parallel providing worthwhile information for the use of this standard.

To illustrate the procedures that should be applied to evaluate the uncertainty affecting the measurements of no-load and load losses during the routine tests on power transformers.

This European Standard covers the oil-immersed single-phase connection assembly of cables for transformers and reactors, designed in accordance with EN 60076 series. NOTE In the standard the term "transformer" is used as common definition for transformer and reactor. The purpose of EN 50299-1 is to establish for the cable assemblies: - the electrical and mechanical requirements, including interchangeability; - the limits of supply; - the test to be carried out. It complements and amends, if necessary, the relevant IEC standards and applies to oil immersed cable connections, suitable for fluid-filled or dry-type cable terminations. EN 50299-1 does not cover direct cable terminations (see 3.1.1.3), but, in this case, upon agreement between purchaser and supplier, the standard may be used for guidance except for Figure 1 and Figure 2 which are not applicable. This standard applies to oil-immersed cable connection boxes on transformers with highest voltage for equipment Um = 72,5 kV to 550 kV, including the current conductor terminal at the cable sealing end of the transformer.

This European Standard covers the oil-immersed single-phase connection assemblies of cables for transformers and reactors designed in accordance with EN 60076 series. NOTE The term "transformer" is used as common definition for transformer and reactor. If no separate cable connection box is used and dry-type cable terminations are directly installed into the transformer tank the requirements of this standard should be followed. The purpose of EN 50299-2 is to establish for the cable connection assemblies: - electrical and mechanical requirements including interchangeability; - limits of supply; - tests to be carried out. It complements and amends, if necessary, the relevant standards and applies to dry-type cable terminations for power cables with extruded insulation which may be used with similar interfaces for the cable entrance in switchgear applications according to EN 62271-209. This standard applies to oil-filled cable connection boxes of transformers with highest voltage for equipment from Um = 72,5 kV to 550 kV, including the conductor current terminal with removable link between the transformer and the dry-type cable termination.

IEC 60214-1:2014 applies to on-load tap-changers of both resistor and reactor types, de-energized tap-changers, and their motor-drive mechanisms. It applies mainly to tap-changers immersed in mineral insulating oil according to IEC 60296 but may also be used for tap-changers with air or gas insulation or immersed in other insulating liquids insofar as conditions are applicable. It applies mainly to tap-changers with arcing contacts but may also be used for arcing-free on-load tap-changers (such as electronic switching) insofar as conditions are applicable. This part of IEC 60214 applies to power and distribution transformers of all types and also to reactors. It does not apply to transformers and reactors mounted on railway rolling stock. This second edition cancels and replaces the first edition published in 2003. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: a) incorporation of requirements on vacuum type on-load tap-changers, b) incorporation of requirements on gas insulated tap-changers, c) changes in the type tests to fit with the service conditions, d) reference to the newest edition of IEC 60076-3:2013.

IEC 60076-14:2013 applies to liquid-immersed power transformers employing either high-temperature insulation or combinations of high-temperature and conventional insulation, operating at temperatures above conventional limits. It is applicable to: - power transformers in accordance with IEC 60076-1; - convertor transformers according to IEC 61378 series; - transformers for wind turbine applications in accordance with IEC 60076-16; - arc furnace transformers; - reactors in accordance with IEC 60076-6. This part of IEC 60076 may be applicable as a reference for the use of high-temperature insulation materials in other types of transformers and reactors. This first edition of IEC 60076-14 cancels and replaces the second edition of the Technical Specification IEC/TS 60076-14 published in 2009. It constitutes a technical revision.

IEC 60076-3:2013 specifies the insulation requirements and the corresponding insulation tests with reference to specific windings and their terminals. This International Standard applies to power transformers as defined by IEC 60076-1. It also recommends external clearances in air. It gives details of the applicable dielectric tests and minimum dielectric test levels. Recommended minimum external clearances in air between live parts and between live parts and earth are given for use when these clearances are not specified by the purchaser. For categories of power transformers and reactors which have their own IEC standards, this standard is applicable only to the extent in which it is specifically called up by cross reference in the other standards. This third edition of IEC 60076-3 cancels and replaces the second edition published in 2000, and constitutes a technical revision. The main changes from the previous edition are as follows: - Three categories of transformer are clearly identified together with the relevant test requirements, these are summarised in Table 1. - Switching impulse levels are defined for values of Um > 72,5 kV. - The procedure for Induced voltage tests with PD has been revised to ensure adequate phase to phase test voltages. - The AC withstand test has been redefined (LTAC instead of ACSD). - Induced voltage tests are now based on Ur rather than Um. - New requirements for impulse waveshape (k factor) have been introduced. - Tables of test levels have been merged and aligned with IEC 60071-1:2010. - Additional test levels have been introduced for Um > 800 kV. - A new Annex E has been introduced, which sets out the principles used in assigning the tests, test levels and clearances in air.

IEC 60076-18:2012 covers the measurement technique and measuring equipment to be used when a frequency response measurement is required either on-site or in the factory either when the test object is new or at a later stage. This standard is applicable to power transformers, reactors, phase shifting transformers and similar equipment.

IEC 61378-1:2011(E) deals with the specification, design and testing of power transformers and reactors which are intended for integration within semiconductor converter plants. The scope of this International Standard is limited to application of power converters of any power rating. Typical applications are: thyristor rectifiers for electrolysis; diode rectifiers for electrolysis; thyristor rectifiers for large drives; thyristor rectifiers for scrap melting furnaces, and diode rectifiers feeding inverters for variable speed drives. The standard also covers the regulating unit utilized in such application as step down regulating transformers or autotransformers. This edition includes the following significant technical changes with respect to the previous edition: - addition of winding connections with phase displacement (30°); - addition of transformers with more than one active part in the same tank; - change of reference power definition; - addition of regulating transformer feeding converter transformer; - addition of considerations about current sharing and hot spot temperature in high current windings for various winding arrangements; - addition of transductors used for d.c. voltage regulation together with diode rectifiers. The contents of the corrigendum of January 2012 have been included in this copy.

IEC 60076-1:2011 applies to three-phase and single-phase power transformers (including auto-transformers) with the exception of certain categories of small and special transformers. For those categories of power transformers and reactors which have their own IEC standards, this part is applicable only to the extent in which it is specifically called up by cross-reference in the other standard. This new edition includes the following significant technical additions with respect to the previous one: - definition of harmonic content; - subclause on transport; - functional method of specification; - connection symbols for single phase transformers; - safety and environmental requirements; - requirements for liquid preservation systems; - clause on DC currents; - vacuum, pressure and leak tests on tanks; - facilities for condition monitoring and environmental and safety considerations.

IEC 60076-2:2011 applies to liquid-immersed transformers, identifies power transformers according to their cooling methods, defines temperature rise limits and gives the methods for temperature rise tests. This new edition includes the following significant technical changes with respect to the previous edition: - the winding hot-spot temperature rise limit was introduced among the prescriptions; - the procedures for the temperature rise test were improved in relation to the new thermal requirements; - five informative annexes were added in order to facilitate the implementation of this standard.

Applies to the following types of reactors: shunt reactors; series reactors including current-limiting reactors, neutral-earthing reactors, power flow control reactors, motor starting reactors, arc-furnace series reactors; filter (tuning) reactors; capacitor damping reactors; capacitor discharge reactors; earthing transformers (neutral couplers); arc-suppression reactors; smoothing reactors for HVDC and industrial application.

Applies to high-voltage/low-voltage self-protected liquid-filled and naturally cooled transformers for rated power 50 kVA to 1 000 kVA for indoor or outdoor use having a primary winding (high-voltage) with highest voltage for equipment up to 24 kV; a secondary winding (low-voltage) with highest voltage for equipment of 1,1 kV.

Identifies the requirements for power transformers to sustain without damage the effects of overcurrents originated by external short circuits. Describes the calculation procedures used to demonstrate the thermal ability of a power transformer to withstand such overcurrents and both the special test and the theoretical evaluation method used to demonstrate the ability to withstand the relevant dynamic effects.

This Technical Report illustrates the procedures and criteria to be applied to evaluate the uncertainty affecting the measurements of no load and load losses during the routine tests on power transformers. Even if the attention is especially paid to the transformers, the document can be also used for the measurements of reactor losses, when applicable.

This Report provides guidance for the evaluation of electromagnetic fields around power transformers. This Report applies to power transformers covered by EN 60076 series with the following characteristics: - apparent rating P: 5 kVA  P  1 000 MVA - insulating level, according to EN 60076-3: • high voltage winding: Um from 7,2 kV to 525 kV • low voltage winding: Um up to 525 kV Reactors are excluded from the present Report. Continuous conducted and radiated emissions are considered for power transformers operating under nominal working conditions of voltage and current. Fault conditions and low occurrence transient events, such as - short-circuits, - lightning and switching transients, - overloads (inrush currents, etc.), - overvoltages, - tap-changer operations, are not considered as normal working conditions. Immunity conditions are considered to ensure the power transformer operates as intended in its normal working environment. The immunity capability of the power transformer is considered for steady state and transient working conditions.

Supersedes EN 50216-5:2002/A1:2002
2021: CLC legacy converted by DCLab NISOSTS

Gives guidance and explanatory comments on the existing procedures for lightning and switching impulse testing of power transformers to supplement the requirements of EN 60076-3. Also generally applicable to the testing of reactors (see EN 60289), modifications to power transformer procedures being indicated where required. Information is given on waveshapes, test circuits including test connections, earthing practices, failure detection methods, test procedures, measuring techniques and interpretation of results.

This Code of Practice gives guidance to users of fully enclosed electrical equipment which is designed to be filled with oil but which may have become contaminated with PCBs. National and Local Authority regulations (if any) take priority. This Code of Practice is applicable to fully enclosed electrical equipment which is designed to be filled with oil but which may have become contaminated with PCBs. This Code of Practice is applicable to electrical equipment which contains more than five litres of insulating and/or cooling liquid. This Code of Practice gives guidance on the precautions to avoid pollution of the environment by the correct installation, maintenance, operation, storage and transportation of oil-filled electrical equipment which may be contaminated with PCBs. This Code of Practice gives guidance on the safety precautions to be taken when handling oil which may be contaminated with PCBs, the refilling of transformers with an oil which does not contain PCBs, the disposal of waste contaminated with PCBs and on the decontamination of oil and electrical equipment. NOTE: The principles contained within this Code of Practice may be applied or if necessary adapted to suit the appropriate circumstances where equipment is filled with insulating liquids other than oil.

This document is part of the EN 50708 series which applies to transformers in compliance with EN 60076 1.

This standard covers the requirements for phase-shifting transformers of all types. The scope excludes transformers with an unregulated phase shift. This document is limited to matters particular to phase-shifting transformers and does not include matters relating to general requirements for power transformers covered in existing standards in the EN 60076 series.

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

This standard covers the requirements for phase-shifting transformers of all types. The scope excludes transformers with an unregulated phase shift. This document is limited to matters particular to phase-shifting transformers and does not include matters relating to general requirements for power transformers covered in existing standards in the EN 60076 series.