Insulating oil testing

Insulating liquids – the lifeblood of transformers

Transformers are designed to be in operation for 40 years or even longer. For the responsible body, their positive economic balance is heavily dependent on avoiding repair times and possible downtimes.


The insulating oil is a decisive criterion for reliable operation. Its ageing condition, which is affected by oxidation, thermal stress, and contact with other materials, essentially determines the service life of the transformer. With BAUR you have an expert partner by your side, enabling you to test the insulating liquid before the transformer fails. The insulating oil testers from BAUR enable you to ensure the reliable operation of your transformers.


Test insulating oil – avoid downtimes


Insulating oil ensures the safe operation of power transformers. In addition to traditional insulating oils, new insulating liquids, such as natural or synthetic ester, are an increasingly popular choice. When insulating liquids are used for cooling and electrical insulation, impurities or ageing can have a huge impact on insulation capacity and result in plant shutdown or even an accident.


In order to prevent this, national and international standards as well as statutory provisions require the regular testing of insulating liquids. The diagnostics of the insulating liquids provides detailed information on the quality of the refining, the purity of the oil, and ageing as well as dielectric losses and dielectric strength. During the quality analysis, the results must be used to determine whether the insulating liquid still provides effective insulation or whether it needs to be reconditioned or changed.

Applications: Checking insulating liquids in transformers | BAUR GmbH

Accurate results for many decades


Even after decades of use, BAUR devices deliver precise measurement results in terms of insulating oil testing and diagnostics because they are designed for hundreds of thousands of oil sample measurements.

This has two advantages. 


  • Comparable measurement results, regardless of the device used
  • Trends can be assessed by comparing current and historic measurement results (even if the historic data was determined using a device of a previous generation)

Software solution for testing and assessment


We offer two series of devices for carrying out breakdown voltage tests and dissipation factor measurements. For both series, the BAUR ITS Lite software simplifies the processing of the measurement results, the customer-specific reporting as well as the data archiving. The BAUR ITS Lite software is used for the automatic transfer of measurement results and for the design and archiving of measurement logs from the BAUR DPA 75 C, DTA 100 C and DTL C oil testers. The logs can be stored in both PDF format and as a flexible text file (*.txt). Extensive language support and the integration of customised logos permit professional log generation.

A global leader for good reason

Applications: Over 20 standards worldwide | BAUR GmbH

Over 20 standards worldwide


BAUR works with universities, laboratories, and standardisation and test bodies to advance the testing of insulating materials and the associated standards. The expertise acquired over the last six decades in the development of our insulating oil testers has been incorporated into national and international standards, which today define the industry standard.

Applications: Report Manager | BAUR GmbH

Report Manager


BAUR Report Manager is used to automatically transfer measurement logs from BAUR oil
testers to a USB drive.

Insulating oil testing: Dissipation factor measurement and breakdown voltage

Applications: Dissipation factor measurement | BAUR GmbH
Applications: Breakdown voltage | BAUR GmbH

Take oil sample correctly

Taking oil samples made easy:


In order to obtain meaningful results from insulating oil testing, oil samples must be properly taken by instructed personnel. Here are a few tips to help you take samples without any issues:

Use a special sample container: for example, a clean aluminium bottle with a capacity of approx. 1 litre.

Store the sealing ring: When opening the sampling nozzle, the sealing ring may get lost when the safety cap is unscrewed. It must remain on the nozzle.

Avoid air bubbles: Removal should be take place using a device that features an inspection window. This ensures any air bubbles are detected. Air bubbles falsify the oil sample. This device is first screwed onto the nozzle.

Pay attention to your surroundings: When taking samples outdoors or in a dirty environment, make sure that no foreign bodies or drops are able to enter the bottle.

Close: After filling the bottle, make sure it is sealed airtight using the screw cap. The bottle needs to be filled to the brim with oil so that no air remains in the bottle neck. After sealing, the bottle can be cleaned, packed and the excess oil can be disposed of.

Flushing: A hose is attached and the oil is removed until no more air bubbles appear. Flushing the hose with one to two litres of oil is usually sufficient.

Flushing the sample bottle: The sample bottle (already cleaned and dried) is then filled with oil, then placed on its side and swivelled or rotated so that the oil dampens the entirety of the wall surface and absorbs any remaining dirt particles. The oil used for flushing the bottle must then be poured out and disposed of properly at a later point.

Taking samples: For the actual sampling, the hose connected to the sampling nozzle should reach to the bottom of the sample container. The bottle is slowly filled to avoid bubbles until it overflows. Up to 50 % of the bottle's contents may overflow. This produces a homogeneous sample without gas pockets. The overflowing oil needs to be collected, e.g. in a bucket, and disposed of properly.

Application video

BAUR's solution expertise in measurement & testing technology: