CLC/SR 10 - Fluids for electrotechnical applications

IEC 62770:2024 describes specifications and test methods for unused natural esters in transformers and similar liquid-immersed electrical equipment in which a liquid is required as an insulating and heat transfer medium. The exposure of natural ester to air leads to deterioration of the insulating liquid. Use of natural esters is therefore restricted to sealed units, or with the conservator tank protected from the contact with atmosphere by a membrane or other suitable system.

IEC 60422:2024 provides monitoring guidance and procedures that are required for the use and maintenance of mineral insulating oils and other hydrocarbon-based liquids in transformers and other electrical equipment, including strategic spares and tanks for holding spare parts and components. This document is applicable to mineral insulating oils, originally supplied conforming to IEC 60296, in transformers, switchgear and other electrical apparatus where oil sampling is reasonably practicable, and where the normal operating conditions specified in the equipment specifications apply. This document is also intended to assist the power equipment operator to evaluate the condition of the oil and maintain it in a serviceable condition. It also provides a common basis for the preparation of more specific and complete local codes of practice. The document includes recommendations on tests and evaluation procedures, and outlines methods for reconditioning and reclaiming oil, and the decontamination of oil contaminated with PCBs. NOTE The condition monitoring of electrical equipment, for example by analysis of dissolved gases, furanic compounds or other means, is outside the scope of this document.

IEC 60567:2023 deals with the techniques for sampling free gases from gas-collecting relays from power transformers. Three methods of sampling free gases are described. The techniques for sampling oil from oil-filled equipment such as power and instrument transformers, reactors, bushings, oil-filled cables and oil-filled tank-type capacitors are no longer covered by this document, but are instead described in IEC 60475:2022, 4.2. Before analysing the gases dissolved in oil, they are first extracted from the oil. Three basic methods are described, one using extraction by vacuum (Toepler and partial degassing), another by displacement of the dissolved gases by bubbling the carrier gas through the oil sample (stripping) and the last one by partition of gases between the oil sample and a small volume of the carrier gas (headspace). The gases are analysed quantitatively after extraction by gas chromatography; a method of analysis is described. Free gases from gas-collecting relays are analysed without preliminary treatment.

This International Standard covers specifications and test methods for unused synthetic aromatic hydrocarbons intended for use as insulating liquid in electrical equipment.

This document describes how the concentrations of dissolved gases or free gases can be interpreted to diagnose the condition of oil-filled electrical equipment in service and suggest future action. This document is applicable to electrical equipment filled with mineral insulating oil and insulated with cellulosic paper or pressboard-based solid insulation. Information about specific types of equipment such as transformers (power, instrument, industrial, railways, distribution), reactors, bushings, switchgear and oil-filled cables is given only as an indication in the application notes. This document can be applied, but only with caution, to other liquid-solid insulating systems. In any case, the indications obtained are given only as guidance with resulting action undertaken only with proper engineering judgment.

This document is applicable to the sampling procedure used for insulating liquids in delivery containers and in electrical equipment such as power and instrument transformers, reactors, bushings, oil-filled cables, oil-filled tank-type capacitors, switchgear and load tap changers (LTCs). This document applies to liquids the viscosity of which at the sampling temperature is less than 1 500 mm2/s (or cSt). It applies to mineral oils and non-mineral oils (such as synthetic esters, natural esters, vegetable oils or silicones).

IEC 60312:2019 defines requirements for the characterization of unused modified esters or blends of unused esters used as insulating liquids for electrotechnical applications. It does not cover liquids that contain any proportion of used liquids. The liquids covered by this document are intended mainly for transformer applications. Unused modified/synthetized esters are derived from a natural or synthetic base, or are blends of both. This document covers a variety of ester liquids not covered by other standards specific to natural esters (IEC 62770) or synthetic esters (IEC 61099). As it addresses various categories of liquids, this document also covers a wide range of values for certain performance characteristics. An important property is viscosity, which can affect the design and cooling performance of electrical equipment. A categorization is defined based on the kinematic viscosity of the different liquids. The category of low viscosity ester liquids is established.

This document provides criteria for the re-use of sulphur hexafluoride (SF6) and its mixtures after recovery and reclaiming from electrical equipment (e.g. for maintenance, at the end-oflife). Sulphur hexafluoride (SF6), nitrogen (N2) and carbon tetrafluoride (CF4), are gases commonly used for electrical equipment. Taking into account environmental concerns, particular attention is paid to re-use criteria for SF6 and its mixtures with N2 and CF4 for its use in electrical equipment. Procedures for recovering and reclaiming used SF6 and its mixtures are outside the scope of this document and are described in IEC 62271-4. This document provides several annexes on the description of the different methods of analysis, on by-products, on the procedure for evaluating the potential health effects from byproducts, on cryogenic reclaiming of SF6, and on reclaiming recommendations. Storage, transportation and disposal of SF6 and its mixtures are outside the scope of this document and are covered by IEC 62271-4. Procedures to determine SF6 leakages are described in IEC 60068-2-17 [4]1. For the purposes of this document, the complementary gases used in SF6 mixtures will be limited to N2 or CF4.

IEC 62961:2018 establishes the measurement of the interfacial tension between insulating liquid and water by means of the Du Noüy ring method close to equilibrium conditions. In order to obtain a value that provides a realistic expression of the real interfacial tension, a measurement after a surface age of approximately 180 s is recorded.

IEC 60376:2018 defines the quality for technical grade sulphur hexafluoride (SF6) and complementary gases such as nitrogen (N2) and carbon tetra-fluoride (CF4), for use in electrical equipment. Detection techniques, covering both laboratory and in-situ portable instrumentation, applicable to the analysis of SF6, N2 and CF4 gases prior to the introduction of these gases into the electrical equipment are also described in this document. This document provides some information on sulphur hexafluoride in Annex A and on the environmental effects of SF6 in Annex B. Information about SF6 by-products and the procedure for evaluating the potential effects of SF6 by-products on human health are covered by IEC 60480, their handling and disposal being carried out according to international and local regulations with regard to the impact on the environment. Handling of SF6 and its mixtures is covered by IEC 62271-4. Procedures to determine SF6 leakages are described in IEC 60068-2-17. For the purposes of this document, the complementary gases used in SF6 mixtures will be limited to N2 or CF4. This third edition cancels and replaces the second edition published in 2005. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: a) the requirements for the use of SF6 in electrical equipment have been confirmed; b) a specification for complementary gases to be used in SF6 mixtures with N2 and CF4 has been included; c) the introduction and scope have been merged; d) a new repartition of the annexes of IEC 60376, IEC 60480 and IEC 62271-4 has been included.

IEC 61125:2018 describes a test method for evaluating the oxidation stability of insulating liquids in the delivered state under accelerated conditions regardless of whether or not antioxidant additives are present. The duration of the test can be different depending on the insulating liquid type and is defined in the corresponding standards (e.g. in IEC 60296, IEC 61099, IEC 62770). The method can be used for measuring the induction period, the test being continued until the volatile acidity significantly exceeds 0,10 mg KOH/g in the case of mineral oils. This value can be significantly higher in the case of ester liquids. Additional test methods such as those described in IEC TR 62036 based on differential scanning calorimetry can also be used as screening tests, but are out of the scope of this document. This second edition cancels and replaces the first edition published in 1992 and Amendment 1: 2004. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: a) the title has been modified to include insulating liquids different from mineral insulating oils (hydrocarbon); b) the method applies for insulating liquids in the delivered state; c) former Method C is now the main normative method; d) precision data of the main normative method has been updated concerning the dissipation factor; e) former Method A has been deleted; f) former Method B has been transferred to Annex B; g) a new method evaluating the thermo-oxidative behaviour of esters is included in Annex C.

IEC 60296:2020 provides specifications and test methods for unused and recycled mineral insulating oils. It applies to mineral oil delivered according to the contractual agreement, intended for use in transformers, switchgear and similar electrical equipment in which oil is required for insulation and heat transfer. Both unused oil and recycled oil under the scope of this document have not been used in, nor been in contact with electrical equipment or other equipment not required for manufacture, storage or transport. Unused oils are obtained by refining, modifying and/or blending of petroleum products and other hydrocarbons from virgin feedstock. Recycled oils are produced from oils previously used as mineral insulating oils in electrical equipment that have been subjected to re-refining or reclaiming (regeneration) by processes employed offsite. Such oils will have originally been supplied in compliance with a recognized unused mineral insulating oil specification. This document does not differentiate between the methods used to recycle mineral insulating oil. Oils treated on-site (see IEC 60422) are not within the scope of this document. Oils with and without additives are both within the scope of this document. This document does not apply to mineral insulating oils used as impregnating medium in cables or capacitors. This fifth edition cancels and replaces the fourth edition published in 2012. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: – This International Standard is applicable to specifications and test methods for unused and recycled mineral insulating oils in the delivered state. – Within the transformer insulating oils, two groups, Type A and Type B, are defined, based on their performance. – A new method for stray gassing under thermo-oxidative stress of mineral insulating oils, which has been tested in a joint round robin test (RRT) between CIGRE D1 and IEC technical committee 10, has been included.

IEC 60599:2015 is available as IEC 60599:2015 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition. IEC 60599:2015 describes how the concentrations of dissolved gases or free gases may be interpreted to diagnose the condition of oil-filled electrical equipment in service and suggest future action. This standard is applicable to electrical equipment filled with mineral insulating oil and insulated with cellulosic paper or pressboard-based solid insulation. Information about specific types of equipment such as transformers (power, instrument, industrial, railways, distribution), reactors, bushings, switchgear and oil-filled cables is given only as an indication in the application notes. This standard may be applied, but only with caution, to other liquid-solid insulating systems. This third edition cancels and replaces the second edition published in 1999 and Amendment 1:2007. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: a) revision of 5.5, 6.1, 7, 8, 9, 10, A.2.6, A.3, A.7; b) addition of new sub-clause 4.3; c) expansion of the Bibliography; d) revision of Figure 1; e) addition of Figure B.4.

IEC 60836:2015 covers specifications and test methods for unused silicone liquids intended for use in transformers and other electrotechnical equipment. Besides the standard transformer applications there are other applications of silicone liquids, such like cable accessories, capacitors, electrical magnets etc. This edition includes the following major technical changes with regard to the second edition: a) classification of liquids according to IEC 61039 have been adapted with respect to the latest edition of IEC 61039:2008; b) classification of liquids according to IEC 61100:1992 have been removed as IEC 61100 has been withdrawn; c) minimum requirements for other silicone liquids for electrotechnical purposes have been added.

IEC 62021-3:2014 describes two procedures for the determination of the acidity of unused and used electrical non-mineral insulating oils. Method A is potentiometric titration and Method B is colourimetric titration. The method may be used to indicate relative changes that occur in non-mineral insulating oil during use under oxidizing conditions regardless of the colour or other properties of the resulting non-mineral oil. The acidity can be used in the quality control of unused non-mineral insulating oil. As a variety of oxidation products present in used non-mineral insulating oil contribute to acidity and these products vary widely in their corrosion properties, the test cannot be used to predict corrosiveness of non-mineral insulating oil under service conditions.

IEC 62770:2013 describes specifications and test methods for unused natural esters in transformers and similar oil-impregnated electrical equipment in which a liquid is required as an insulating and heat transfer medium. Natural esters with additives are within the scope of this standard. Because of their different chemical composition, natural esters differ from insulating mineral oils and other insulating fluids that have high fire points, such as synthetic esters or silicone fluids. Natural, ester-derived insulating fluids with low viscosity have been introduced but are not covered by this standard. Pertinent properties of such fluids are given in Annex B. This standard is applicable only to unused natural esters. Reclaimed natural esters and natural esters blended with non-natural esters fluids are beyond the scope of this standard.

IEC 60422:2013 gives guidance on the supervision and maintenance of the quality of the insulating oil in electrical equipment. This International Standard is applicable to mineral insulating oils, originally supplied conforming to IEC 60296, in transformers, switchgear and other electrical apparatus where oil sampling is reasonably practicable and where the normal operating conditions specified in the equipment specifications apply. This International Standard is also intended to assist the power equipment operator to evaluate the condition of the oil and maintain it in a serviceable condition. It also provides a common basis for the preparation of more specific and complete local codes of practice. The standard includes recommendations on tests and evaluation procedures and outlines methods for reconditioning and reclaiming oil and the decontamination of oil contaminated with PCBs. This fourth edition cancels and replaces the third edition, published in 2005, and constitutes a technical revision. The main changes with respect to the previous edition are as follows: - This new edition represents a major revision of the third edition, in order to bring in line this standard with latest development of oil condition monitoring, containing new limits for oil parameters, suggested corrective actions in the tables and new test methods. - The action limits for all oil tests have been revised and changes made where necessary to enable users to use current methodology and comply with requirements and regulations affecting safety and environmental aspects. - In addition, this standard incorporates changes introduced in associated standards since the third edition was published.

IEC 62697-1:2012 specifies a test method for the quantitative determination of corrosive sulfur compounds-dibenzyl disulfide (DBDS) in used and unused insulating liquids over a 5 to 600 mg kg-1 concentration range.

Issued by CLC/BTTF 116-1 converted into CLC/TC 10 (D145/093) * 2012-03-09: Publication editing allocated to cpalagi@cencenelec.eu

IEC 60475:2011 is applicable to the procedure to be used for insulating liquids in delivery containers and in electrical equipment such as power and instrument transformers, reactors, bushings, oil-filled cables, oil-filled tank-type capacitors, switchgear and load tap changers. The main changes with respect to the previous edition are as follows: - withdrawal of askarels; - addition of recommendations concerning general health, safety and environmental protection; - additional details regarding the sampling of oil from electrical equipment, using various types of sampling devices appropriate for the different types of oil tests to be performed in the laboratory.

IEC 61099:2010 covers the specification and test methods for unused synthetic organic esters. It applies to synthetic organic esters, delivered to the agreed point and time of delivery intended, for use in transformers, switchgear and similar related equipment in which synthetic organic esters are required as an insulant and for heat transfer. The main changes of this new edition with respect to the previous one relate to the aim of giving a more updated specification of synthetic organic esters when used as insulating liquids.

IEC 60666:2010 provides methods concerning the detection and determination of specified additives in unused and used mineral insulating oils. The detection methods may be applied to assess whether or not a mineral insulating oil contains an additive as specified by the supplier. The determination methods are used for the quantitative determination of additives known to be present or previously detected by the appropriate detection method. The main changes with respect to the previous edition are listed below: - a change in the title from 'Detection and determination of specified anti-oxidant additives in insulating oils'; - new Annexes B and C which provide methods for the determination of two additives different from the anti-oxidants.

IEC 62535:2008 specifies a test method for detection of potentially corrosive sulphur in used and unused mineral insulating oil. Most recent failures due to corrosive sulphur are related to the formation of copper sulphide deposits in and on the surface of winding cellulosic paper. The test method uses a copper conductor, wrapped with one layer of paper, immersed in the oil and heated to evaluate the capability of the oil to yield copper sulphide and transfer it to paper layers. The growth of copper sulphide on bare copper may cause the presence of conductive particulates in the oil, which can act as nuclei for electrical discharge and may lead to a fault. Other test methods exist using a bare copper strip immersed in oil and heated to detect the corrosive behaviour of oil against copper. ASTM D1275 Method B is also used for this test and a modified procedure using low oil volumes is included in Annex A. Tests with and without paper are considered as complementary and may lead to different results.

IEC 61039:2008 establishes the detailed classification of the N family (insulating liquids) that belongs to class L (lubricants, industrial oils and related products) in accordance with ISO 8681 and ISO 6743-99, affecting product categories that include products derived from petroleum processing, synthetic chemical products and synthetic and natural esters. The main change with regard to the previous edition concerns the updating of the classification of insulating liquids, taking into account the largest number possible of substances that have, or may have, possible application in electrical components.

Describes the sampling procedures and methods for the determination of particle concentration and size distribution. Three methods are specified. One uses an automatic particle size analyser, working on the light interruption principle. The other two use an optical microscope, in either the transmitted light or incident light mode, to count particles collected on the surface of a membrane filter. The optical microscope methods are described in ISO 4407. All three methods are applicable to both used and unused insulating liquids. Annex A contains an alternative sampling procedure using a syringe and Annex B reports a reference for the calibration of automatic particle counters. The significant technical changes with respect to the previous edition are as follows: - new calibration procedures for automated laser particle; - three figures contamination code; - new procedure of sample pre-treatment when automated laser counter method are used.

Describes a procedure for determination of the acidity of unused and used electrical mineral insulating oils. The method may be used to indicate relative changes that occur in a mineral insulating oil during use under oxidizing conditions that may or may not be shown by other properties of the resulting mineral oil. The acidity can be used in the quality control of unused mineral oil. As a variety of oxidation products present in used mineral oil contribute to acidity and these products vary widely in their corrosion properties, the test cannot be used to predict corrosiveness of a mineral oil under service conditions.

Specifies oil-sampling procedures, analysis requirements and procedures, and recommends sensitivity, repeatability and accuracy criteria for the application of dissolved gas analysis (DGA) to factory testing of new power transformers, reactors and instrument transformers filled with mineral insulating oil when DGA testing has been specified. The most effective and useful application of DGA techniques to factory testing is during the performance of long-term tests, typically temperature-rise (heat run) and overloading tests on power transformers and reactors, also impulse tests on instrument transformers. DGA may also be valuable for over-excitation tests run over an extended period of time. Experience with DGA results, before and after short-time dielectric tests, indicates that DGA is normally less sensitive than electrical and acoustic methods for detecting partial discharges. However, DGA will indicate when these partial discharges become harmful to the insulation and may be detected by inspection [2]. This edition includes the following significant technical changes with respect to the previous edition: a) the specific procedures used during factory tests (sampling location, sampling frequency, gas extraction and chromatographic analysis in the laboratory) are described in more detail; b) information is provided in Annex A concerning the residual gas contents recommended before thermal tests on power transformers, typical gas values observed during the tests and cases where gas formation during the tests was followed by problems in the transformers; c) typical values observed during chopped lightning-impulse tests on instrument transformers are indicated in Annex B.

The scope of this Technical report is to provide guidance for the activities of inventory, control, management, decontamination and/or disposal of equipment and containers with insulating liquid containing PCBs, in compliance with the Council Directives (96/59/EC), using Best Available Techniques - BAT - (96/61/EC), Commission Decision (2001/68/EC), Stockholm Convention on Persistent Organic Pollutants (POPs) and/or with appropriate national or local legislation. This Technical report is addressed, in particular, toward the Life Cycle Management (LCM) of insulating liquids and it has been developed in accordance with the following objectives: a) reduction of risks for workers, public health and the environment, arising from human error, malfunction, or failures of the equipment that could cause fires or spillage of hazardous and Persistent Organic Pollutants (POPS)s; b) implementation of the “Best Available Techniques” (BAT),”Best Environmental Practices”(BEP)and methodologies available for safety, whilst taking into account the surroundings and the criteria of self-sufficiency and functional recovery; c) technical feasibility of the activities within the prescribed time schedules, taking into account current legislation and economic feasibility. NOTE 1 For those CENELEC countries in which the European Directives do not apply, this Technical report has an informative purpose only. Different limits from those given in the present Technical report are required in some countries. NOTE 2 For those countries outside of European Community the Stockholm Convention on Persistent Organic Pollutants (POPs) should be applied. NOTE 3 When reading this Technical report, reference should also be made to Annex C of EN 50195 and Annex B of EN 50225, because in some EU countries (i.e. France, Italy, Poland, Spain, etc.) there are other mandatory requirements.

Describes methods for the determination of the dielectric dissipation factor, relative permittivity and d.c. resistivity of any insulating liquid material at the test temperature. The methods are primarily intended for making reference tests on unused liquids. They can also be applied to liquids in service in transformers, cables and other electrical apparatus. However the method is applicable to a single phase liquid only. When it is desired to make routine determinations, simplified procedures, as described in Annex C, may be adopted. With insulating liquids other than hydrocarbons, alternative cleaning procedures may be required. The main changes from the previous edition deal with the preferred measurement method.

Describes the procedure for the determination of the acidity of unused and used electrical mineral insulating oils. The method may be used to indicate relative changes that occur in a mineral insulating oil during use under oxidizing conditions regardless of the colour or other properties of the resulting mineral oil. The acidity can be used in the quality control of unused mineral oil. As a variety of oxidation products present in used mineral oil contribute to acidity and these products vary widely in their corrosion properties, the test cannot be used to predict corrosiveness of a mineral oil under service conditions. The acidity results obtained by this test method may or may not be numerically the same as those obtained by colorimetric methods, but they are generally of the same magnitude.

This European Standard specifies testing procedures for fibrous wipers to be used with equipment normally containing electrical insulating oil. Such testing is necessary to rank commercial products, so that possible contamination of insulating oil and electrical equipment with fibres during maintenance operations may be minimized.

This standard describes the method of determining fibre contamination of mineral insulating oil used in electrotechnical equipment by counting the number of fibres on the surface of a membrane filter

Specifies a procedure for the determination of the kinematic viscosity of mineral insulating oils, both transparent and opaque, at very low temperatures, after a cold soaking period of at least 20 h, by measuring the time for a volume of liquid to flow under gravity throught a calibrated glass capillary viscometer. Applies at all temperatures to both Newtonian and non-Newtonian liquids having viscosities of up to 20 000 mm2/s.

Describes a method for simultaneous measurement of conductance G and capacitance C enabling the calculation of the dielectric dissipation factor tan delta of insulating liquides. Method applies to both unused insulating liquids and insulating liquids in service in transformers and in other electrical equipment.

Describes methods for the determination of water in insulating liquids and in oil-impregnated cellulosic insulation with coulmetrically generated Karl Fischer reagent.

Specifies a method for the determination of polychlorinated biphenyl (PCB) concentration in non-halogenated insulating liquids by high-resolution capillary column gas chromatography using an electron capture detector (ECD). Gives total PCB content; especially useful when a detailed analysis of PCB congeners is necessary.

Describes an empirical test procedure intended to indicate the presence of contaminants such as water and solid suspended matter, and the advisability of carrying out drying and filtration treatment. Standardized testing procedures and equipment are essential for the unambiguous interpretation of test results.

Applies to all insulating liquids, used and unused, the kinematic viscosity of which is lower than or equal to 300 mm2/s at 40 °C.

Guide to the maintenance of synthetic organic esters, originally complying with the requirements of EN 61099, in transformers with rated voltages up to 35 kV.

Specifies test methods for the analysis of 2-furfural and related furan compounds resulting from the degradation of cellulosic insulation and found in mineral insulating oil samples taken from electrical equipment.

Covers specifications and test methods for unused synthetic aromatic hydrocarbons intended for use as insulating liquid in electrical equipment.

Describes a method for assessing the changes in activity of pour point depressant additives in inhibited and uninhibited mineral insulating oils when aged in the presence of insulating kraft paper.

Describes a method for measuring the oxygen index of insulating liquids. This test method is applicable to all liquids, the viscosity of which is lower than or equal to 50 mm2/s at 40°C ± 1°C.

Covers specifications and test methods for unused polybutenes, as delivered, intended for use as insulating liquids in electrical equipment.

Covers specifications and test methods for unused mineral insulating oils, as delivered, intended for use in cables with oil ducts. These include hollow core cables, pipe type cables and any others in which provision is made for the oil to flow.

Describes two procedures each using different apparatus to measure the tendency of insulating liquids to evolve or absorb gas when subjected to electrical stress.

Applies to quality control and acceptance testing of oils. Two methods of analysis are given: infra-red spectrophotometry and adsorption chromatography.