Transformer Oil — IEC 60422 / IEC 60567 DGA / IEC 60156

What Is Transformer Oil?

Transformer oil analysis assesses whether the oil maintains both its insulation and cooling function, and whether a fault is developing inside the transformer. The basic tests are breakdown voltage (IEC 60156), water content, acidity, dielectric dissipation factor and interfacial tension. DISSOLVED GAS ANALYSIS (DGA, IEC 60567/60599) diagnoses the fault type from the distribution of gases dissolved in the oil.

Purpose of Transformer Oil

The purpose is to monitor the transformer's insulation condition and detect internal faults such as partial discharge, overheating, or arcing early. Transformer failure causes both a costly and long-duration outage.

Which Products Is Transformer Oil Applied To?

Power transformers
Distribution transformers
Reactors and tap changers
Oil circuit breakers
New and reclaimed insulating oils

In Which Sectors Is Transformer Oil Used?

Oil & GasPetrokimyaEnergyEnergyElectrical

Standards Related to Transformer Oil

IEC 60422 (monitoring and maintenance of mineral insulating oils)
IEC 60156 (determination of breakdown voltage)
IEC 60567 (sampling and analysis of gases from oil)
IEC 60599 (interpretation of dissolved gas analysis)
IEC 60814 (water content — Karl Fischer)
IEC 62021 series (determination of acidity)
IEC 60247 (dielectric dissipation factor and resistivity)

Transformer Oil Conditions

Sampling: According to IEC 60475; Air contact and moisture ingress must be prevented
DGA numunesi: It should be taken in a gas-tight syringe or special container, free of air bubbles.
Temperature: Oil temperature is recorded during sampling
Disposition: DGA interpretation is based on gas rise rate rather than a single measurement

Equipment for Transformer Oil

Breakdown voltage test set
Gas chromatograph (DGA)
Karl Fischer titrator
Dielectric dissipation factor measurement cell
Automatic titrator (acidity)
Interfacial tension tensiometer

Sample Requirements for Transformer Oil

A sampling setup compliant with IEC 60475 must be used
The DGA sample must be taken with a gas-tight syringe, leaving no air bubbles
Sampling date, oil temperature and load condition must be recorded
Transformer information (power, age, previous results) must be provided

Duration of Transformer Oil

Physical and chemical tests are completed quickly. DGA analysis requires interpretation after the chromatographic measurement; the result is generally reported within a few working days.

Transformer Oil Procedure

1The sample is taken per IEC 60475.
2Appearance and colour are assessed.
3Breakdown voltage is measured.
4Water content is determined by Karl Fischer.
5Acidity, interfacial tension and dissipation factor are measured.
6DGA is performed and interpreted per IEC 60599.

Transformer Oil Acceptance Criteria

IEC 60422 recommends action values for breakdown voltage, water content and acidity according to the transformer's voltage class and age. For DGA, gas increase rate and gas ratios are more decisive than an absolute limit; IEC 60599 defines interpretation methods.

Evaluation of Results

DGA's strength is in diagnosis: presence of acetylene indicates arcing, high ethylene overheating, and high hydrogen and methane are signs of partial discharge. However, interpretation must rely on historical data, not a single measurement. Water content reflects the condition not only of the oil but also of the paper insulation, and migrates between oil and paper depending on temperature.

Transformer Oil Report

Transformer information and sampling conditions
Appearance, colour and breakdown voltage
Water content, acidity, interfacial tension and dissipation factor
Dissolved gas concentrations
Interpretation and fault-type assessment per IEC 60599
Trend comparison with previous results

Accreditation

EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.

Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.

Scope and authorisations

Related Regulations

(EU) 548/2014 Ecodesign Regulation for Transformers (for relevant products)

Petroleum, Fuel and Oil Analysis — What Does This Testing Field Cover?

The section below describes the field that the Transformer Oil test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.

Petroleum, fuel and oil analysis determines whether a fluid meets its specification and how it behaves in use. Standards in this field consist largely of ASTM and EN publications, with a separate method defined for each parameter.

What distinguishes this family is that product specifications are written as PARAMETER LISTS. Specifications such as EN 590 (diesel), EN 228 (petrol), EN 14214 (biodiesel) and ISO 8217 (marine fuels) state for each parameter both the limit and the method by which that limit is to be measured. If the method changes the result may change too; the specification therefore binds the method as well, and the use of an "equivalent method" is possible only where the specification allows it.

On the fuel side, parameters describe three different properties of the product. Physical properties (density, viscosity, distillation curve, pour point, cloud point) determine pumpability and cold weather behaviour. Combustion properties (cetane number, octane number, calorific value) indicate performance in the engine. Contaminant and stability parameters (sulphur, water, sediment, oxidation stability, copper strip corrosion) affect both emissions and storage life.

Oil analysis is carried out for two different purposes and the two must not be confused. Analysis of NEW oil verifies the conformity of the product to its specification: viscosity index, additive content, flash point. Analysis of USED oil, by contrast, is done to read the condition of the machine — elemental analysis shows wear metals (iron, copper, chromium, aluminium), water and fuel contamination point to leaks, and oxidation and acid number determine the remaining life of the oil.

Used oil analysis is therefore a PREDICTIVE MAINTENANCE tool. The trend of samples taken at regular intervals is followed; it is the trend rather than a single result that is meaningful. Iron levels climbing over the course of months allow intervention before a failure occurs.

Marine fuels are the most active sub-body of the field. The global tightening of sulphur limits has brought new blended fuels onto the market; for these fuels stability, compatibility (whether two fuels form deposits when mixed) and catalytic fines content have become critical parameters.

Sampling is part of the result in this family too. A sample taken from the bottom of a tank shows different water and sediment content from one taken from the upper level; in commercial deliveries the sampling point and method are set by contract.

Method groups in this field

Physical properties
Density (oscillating U-tube and hydrometer), kinematic viscosity, distillation, pour and cloud point, flash point.
Combustion properties
Cetane number and cetane index, research and motor octane number, calorific value.
Sulphur and elements
Sulphur by UV fluorescence and XRF; elemental analysis and additive content by ICP.
Stability and corrosion
Oxidation stability, copper strip corrosion, water and sediment, filter blocking tendency.
Composition analysis
Boiling range distribution by gas chromatography, hydrocarbon types (FIA), benzene and aromatics content, fatty acid methyl ester content.
Used oil
Wear metals, contamination (water, fuel, soot), oxidation, acid and base number, change in viscosity.

Commonly confused in this field

The specification binds the method as well; a result measured by a different method may not be accepted for specification conformity.
A single result on used oil is not meaningful; the decision is made on the trend.
The sampling point determines the result; the tank bottom and the upper level show different water and sediment.
The cetane index is a calculated value and is not the same thing as a measured cetane number.
Fuels blended with biodiesel behave differently in terms of storage life and microbial growth; classical diesel parameters are not sufficient.
Mixing marine fuels from different sources can cause deposits; compatibility is assessed separately.

Which decisions these results support

Conformity of a fuel lot to specification and commercial delivery
Predictive maintenance decisions based on used oil analysis
Determining parameters for customs and tax classification
Quality verification after storage, blending and transport
Compliance with sulphur limits under emissions legislation

Related Tests

Frequently Asked Questions About Transformer Oil

Acetylene appeared in the DGA — what should we do?

Acetylene is generally an indicator of arcing or high-energy discharge and must be taken seriously. Re-sampling is done in case of a sampling error; if confirmed, the increase rate is monitored and assessed together with electrical tests.

Does oil filtration solve the problems?

It is effective for water, particulates, and to some extent acidity. However, it does not eliminate the electrical fault indications seen in DGA; filtration only temporarily masks the symptom by removing the gases. The source of the fault must be investigated separately.