Specialist of transformers’ oil analysis for more than 40 years, IESPM answers to your questions on oil testing and analysis, guides you and assists you in the conditional maintenance of your transformers.

Why is it necessary to perform oil analysis on transformers ?

In industrial units, if the change of a transformer is not planned, a damage on it can pull a loss of partial or total production from few hours to several months depending on the impacted transformer.

A regular follow-up of the state of the oil contained in your transformers thus represents a major interest in your program of maintenance. Indeed, the oil of transformer plays a key role in the proper functioning of the transformers. Analysing regularly the oil of transformer allows to reveal several kind of anomalies (electric, thermal defects, premature ageing, loss of insulating capacity, etc.).

The control of the oil of transformers presents many interesting points :

• it could help you prolong the lifetime of the transformers
• it answers PCB regulation on the oil of transformers
• it provides estimated elements to manage costs of maintenance (cost of treatment, depollution, replacement, etc.)
• it  could avoid the stop of production led by a breakdown
• it provides the necessary information to all parties for the compulsory follow-up of the transformers

What is a transformer oil analysis ?

A transformer oil analysis is composed of several types of tests to realise a relevant diagnostic. The first one consists to analyse dissolved gases in the dielectric fluid (the oil of transformer). The concentrations give a precise indication on the conditions of functioning of the equipment. So, We can identify the faults such as heatings or electric defects.

The second series of tests consists to verify the state of oil of the transformer by realising different measures, such as :

• The breakdown voltage which allows to determine the threshold from which the dielectric fluid submitted to an electric field lose its insulating function.
• The moisture content : when it raises, could decrease the breakdown voltage and reduce the lifetime of the transformer (by accelerating the degradation of the paper).
• The acidity which allows to follow the “ageing” of the dielectric fluid by analysing the content in acids componement stemming from its degradation.
• The PCB content (polychlorinated biphenyls). Indeed, according to the local regulations, the fluids containing more than 50 ppm of PCB must be eliminated and carry to a processing center submitted to authorization.
• The corrosivity of the oil (presence of DBDS1 and highlighting of corrosive sulfur) to avoid a premature ageing of the transformer.

The third analysis concerns the cellulose paper isolating the reels of the transformer, and also the search of furan derivatives which come from the degradation of the cellulose. The analysis allows to determine the degradation level of the insulating material.

What is the periodicity recommended to analyse oil of transformer ?

The monitoring frequencies defined below are based on more than 50 years of experience and on the recommendations of the standard CEI 60422. Theses frequencies depend on the category and on the age of the transformer :

IESPM recommendations table

What is the cost of a transformer oil analysis ?

The sampling cost of the dielectric fluid depends on the complexity of the installation and on the accessibility. It is often lower than €1000.
Regarding the cost of analyses, is about €200 by transformer according to the number, and to the method of measures realised.
Our analysis laboratory assists you in the follow-up of your transformers by realising the sampling of oil on your transformer or by supplying to you an oil analysis kit adapted to transformers.

With the analysis of our laboratory, we dress a complete diagnostic of the state of the oil of your transformer and advice you on the actions to undertake.
To know more on dielectric fluid analysis by IESPM

Let’s meet our experts on the next event to expose us your issues on transformer oil analysis.

CIGRE Congress, from the 26th to the 31rst of august 2018, Congress Center in Paris. (IESPM stand n° 227, Level 2)

IESPM also proposes a special training dedicated to the monitoring of transformers by the technique of dielectric fluid analysis

Consult our training course program « monitoring of transformers »

This post is also available in: French