T.E Laboratories Ltd, operate Ireland’s only transformer oil analysis laboratory. Since 2007 we have tested samples for a majority of company’s including ESB.

Condition based monitoring techniques are already well established for many plant items such as pumps, motors, gearboxes, etc. But what about the units which supply power to your plant, the faithful, but often forgotten, transformer.

Transformer Oil Quality Services

  • ISO9001 certified testing
  • Fast turnaround times
  • Comprehensive suite of transformer fluid analysis services
  • A single point of contact for our testing and advice services

View our transformer oil analysis brochure here.


Moisture Content:
It is important to monitor moisture content as water, in minute quantities, is harmful in power equipment because it is attracted to the places of greatest electrical stress and this is where it is the most dangerous.

Breakdown Voltage or Dielectric Strength:
A measure of the ability of the oil to withstand electric stress (voltage) without failure. Oils with high breakdown voltage are deemed good electrical insulators. Contaminants such as water, sediment and conducting particles (dirt) reduce the breakdown voltage of insulating oil.

Dissipation & Resistivity Factors:
The Dissipation test measures the leakage current through oil, which is the measure of the contamination or deterioration. The test is not specific in what it detects i.e. more a screening test. Resistivity is a reliable indicator of the condition of transformer oil, low resistivity values being a sign of oil, which contains particulate contaminants and oxidative products.

Total Acid Number (Acidity Content):
The TAN value indicates the potential of corrosion problems within a system. As the acid number increase (usually due to oxidation of the oil) the insulating quality of the oil (and paper) decreases.

Interfacial Tension:
Interfacial tension test of transformer oils is an indicator of the presence of oil decay products (acids) and soluble polar contaminants from solid insulating materials. The greater the concentration of contaminants, the lower the IFT.

Dissolved Gas Analysis:
The amounts and types of gases found in the oil are indicative of the severity and type of fault occurring in the transformer. The types of gases we are concerned with are Hydrogen, Methane, Ethane, Ethene, Acetylene, Carbon Dioxide and Carbon Monoxide.

Interpretation of Gas Analysis Results
There are various international guidelines on interpreting DGA. The most frequently used is the Rogers Ratio Method

The Rogers Ratio Method diagnoses faults using 3 gas ratios:

C2H2/C2H4, CH4/H2, C2H4/C2H6

This indicates the following types of faults:

  • Normal ageing, partial discharge, low and high energy density
  • High energy of thermal faults and electrical faults

Furan Analysis & Degree of Polymerization:
The mechanical properties of insulating paper can be established by measurement of the degree of polymerization (DP). This is determined by

This is determined by analysing the oil for the presence of 2-Furaldehyde. Using the amount/concentration of the 2-Furaldehyde found in the oil the DP can be calculated.

PCB Analysis:
PCB analysis detects the presence of polychlorinated biphenyls in transformer oil. These toxic organic pollutants were used extensively in transformers for decades because of their ideal properties for use in transformers. The analysis is performed under ISO 17025 accreditation using the IEC61619 standard method.

DBDS Analysis:
Oil containing reactive sulphur species identified in most cases as dibenzyldisulfide (DBDS) can react with copper to form copper sulphide on the surface of the conductors and on the paper insulation surfaces even under normal operating conditions of transformers. Oil with a high concentration of DBDS is susceptible to the formation of corrosive Sulphur.

Advantages for having routine transformer oil analysis

  • Protection against expensive in-service failures
  • Possible reduced insurance charges
  • Ability to schedule maintenance
  • Reduce maintenance costs
  • PCB analysis when required
  • Advice on transformer condition

Oil Tests Provided

Dissolved Gas Analysis

Dielectric Breakdown Strength

Furans & Degree of Polymerization


Resistivity & Dissipation Factor


Moisture Content


Standard Used Test Name
ISO 6295 Interfacial Tension
IEC 62021-1 Total Acid Number
IEC 60814 Moisture Content
IEC 60247 Power (Dissipation) Factor
IEC 60156/1995-05 Dielectric Breakdown Voltage
D1524-94 Colour
IEC 61619 Determination of PCB content
BS 61198:1994 Determination of Furan content

If you require more information on Transformer Oil Analysis please email: or call us on 059 9152881

Alternatively, fill out the form below and we will contact you shortly.

Send us mail