IEC 60422 Mineral Insulating Oils in Electrical Equipment
IEC 60422 Mineral Insulating Oils in Electrical Equipment - Supervision and Maintenance Guidance
1 Scope
This International Standard gives guidance on the supervision and maintenance of the quality of the insulating oil in electrical equipment.
This 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 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.
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 standard.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
IEC 60156, Insulating liquids - Determination of the breakdown voltage at power frequency - Test method
IEC 60247, Insulating liquids - Measurement of relative permittivity, dielectric dissipation factor (tan δ) and d.c. resistivity
IEC 60296:2012, Fluids for electrotechnical applications - Unused mineral insulating oils for transformers and switchgear
IEC 60475, Method of sampling liquid dielectrics
IEC 60666:2010, Detection and determination of specified additives in mineral insulating oils
IEC 60814, Insulating liquids - Oil-impregnated paper and pressboard - Determination of water by automatic coulometric Karl Fischer titration
IEC 60970, Insulating liquids - Methods for counting and sizing particles
IEC 61125:1992, Unused hydrocarbon based insulating liquids - Test methods for evaluating the oxidation stability
IEC 61619, Insulating liquids - Contamination by polychlorinated biphenyls (PCBs) - Method of determination by capillary column gas chromatography
IEC 62021-1, Insulating liquids - Determination of acidity - Part 1: Automatic potentiometric titration
IEC 62021-2, Insulating liquids - Determination of acidity - Part 2: Colourimetric titration
IEC 62535:2008, Insulating liquids - Test method for detection of potentially corrosive sulphur in used and unused insulating oils
ISO 2049, Petroleum products - Determination of colour (ASTM scale)
ISO 2719, Determination of flash point - Pensky-Martens closed cup method
ISO 3016, Petroleum products - Determination of pour point
ISO 3104, Petroleum products - Transparent and opaque liquids - Determination of kinematic viscosity and calculation of dynamic viscosity
ISO 3675, Crude petroleum and liquid petroleum products - Laboratory determination of density - Hydrometer method
ISO 4406:1999, Hydraulic fluid power - Fluids - Method for coding the level of contamination by solid particles
EN 14210, Surface active agents - Determination of interfacial tension of solutions of surface active agents by the stirrup or ring method
ASTM D971, Standard Test Method for Interfacial Tension of Oil Against Water by the Ring Method
ASTM D1275:2006, Standard Test Method for Corrosive Sulfur in Electrical Insulating Oils
DIN 51353: Testing of insulating oils; Detection of corrosive sulphur; Silver strip test
3 Terms and definitions
For the purposes of this document, the following definitions apply.
3.1 local regulations
regulations pertinent to the particular process in the country concerned
Note 1 to entry: Such regulations may be defined by local, regional or national legislation or even the owner or operator of the equipment itself. They are always to be considered as the most stringent of any combination thereof. It is the responsibility of each user of this standard to familiarize themselves with the regulations applicable to their situation. Such regulations may refer to operational, environmental or health and safety issues. A detailed risk assessment will usually be required.
3.2 routine tests (Group 1)
minimum tests required to monitor the oil and to ensure that it is suitable for continued service
Note 1 to entry: If the results obtained from these tests do not exceed recommended action limits usually no further tests are considered necessary until the next regular period for inspection but, under certain perceived conditions, complementary tests may be deemed prudent.
3.3 complementary tests (Group 2)
additional tests, which may be used to obtain further specific information about the quality of the oil, and may be used to assist in the evaluation of the oil for continued use in service
3.4 special investigative tests (Group 3)
tests used mainly to determine the suitability of the oil for the type of equipment in use and to ensure compliance with environmental and operational considerations
3.5 reconditioning
process that eliminates or reduces gases, water and solid particles and contaminants by physical processing only
3.6 reclamation
process that eliminates or reduces soluble and insoluble polar contaminants from the oil by chemical and physical processing
3.7 PCB decontamination
process that eliminates or reduces PCB contamination from mineral oil
4 Properties and deterioration/degradation of oil
The reliable performance of mineral insulating oil in an insulation system depends upon certain basic oil characteristics that can affect the overall performance of the electrical equipment.
In order to accomplish its multiple roles of dielectric, coolant and arc-quencher, the oil needs to possess certain properties, in particular:
• high dielectric strength to withstand the electric stresses imposed in service
• sufficiently low viscosity so that its ability to circulate and transfer heat is not impaired
• adequate low-temperature properties down to the lowest temperature expected at the installation site
• resistance to oxidation to maximize service life
In service, mineral oil degrades due to the conditions of use. In many applications, insulating oil is in contact with air and is therefore subject to oxidation. Elevated temperatures accelerate degradation. The presence of metals, organo-metallic compounds or both may act as a catalyst for oxidation. Changes in colour, the formation of acidic compounds and, at an advanced stage of oxidation, precipitation of sludge may occur. Dielectric and, in extreme cases, thermal properties may be impaired.
In addition to oxidation products, many other undesirable contaminants, such as water, solid particles and oil-soluble polar compounds can accumulate in the oil during service and affect its electrical properties. The presence of such contaminants and any oil degradation products are indicated by a change of one or more properties as described in Table 1.
Deterioration of other constructional materials, which may interfere with the proper functioning of the electrical equipment and shorten its working life, may also be indicated by changes in oil properties.
