Transformers Dielectric Oil Sampling Procedure

The oil samples are collected from each transformer, marked, transported, and delivered by trained personnel to a certified laboratory. That accredited the oil samples of our clients’ equipment is within the specifications for a smooth operation. This practice of sampling electrical insulating liquids is as per accordance with ASTM D923–15, and its results as per IEEE C57.106-2006 and IEEE C57.104-2008.
To obtain the required information and determine the maintenance action or procedure to follow in each case, preventing, minimizing, or eliminating risks and managing the life of the transformers. Dielectric and Physicochemical Analysis for Transformer Dielectric Oil (DPAT)

The Dielectric and Physicochemical Analysis aims to diagnose the condition of the insulating paper in terms of its percentage of water and degree of impregnation of oxidation products generated by the insulating oil of the transformer. Defines the type of maintenance that the transformer may require to guarantee its useful life.

Analysis to be performed:

Dielectric strength
Moisture Content
Neutralization Number
Relative density
Interface Tension
Power Factor At 25 ° C
Power Factor At 100 ° C

Possible Results

The transformer in a normal situation or the oil is in an incipient degree of degradation (Action 1).
Preservation of insulating paper, water and oxidation products (Action 2).
If the transformer is in critical condition due to lack of maintenance (Action 3).
Actions to Take According to Results:
1. Follow up every 6 or 12 months.
2. Scheduled maintenance, according to the degradation state of the insulating paper.
3. Evaluate the cost of maintenance and the remaining useful life of the transformer.

Chromatography of Dissolved Gases in Dielectric Oil

The Chromatographic Analysis of Dissolved Gases in the insulating oil aims to detect the presence of combustible gases such as Hydrogen, Carbon Monoxide, Methane, Ethylene, Acetylene and others such as Carbon Dioxide and thus predict or rule out the existence of term-type failures and or electrical as internal discharges, corona effects, and oil or cellulose overheating. This analysis allows us to monitor the transformer in operation and schedule the service output of a unit for internal inspection (if necessary) and avoid an unexpected failure.
This test is carried out in our laboratory, using cutting – edge Gas Chromatograph.

Factors to Detect:

  • Representative gases in the different faults.
  • Total or partial acceptable gas levels.
  • Speed in gas generation.
  • Crown effect or partial discharges.
  • Gas groups generated by a given fault.
Analysis of Inhibitors Content

The test consists of gas chromatography in which the oxidation inhibitor content is determined (DiButil Para-Cresol, DBPC; or DiButil-Phenol, BP), which must comply with ASTM Standard D-4768-03 ( 0.08% for Type I oils, and 0.3% for type II oils).
They are additives that protect the insulating oil from the natural oxidation process. Inhibitors allowed by ASTM D-3487:
2,6-Ditert-Butyl Phenol
2, 6-Ditert-Butyl for Cresol
Biphenyl Content Analysis Polychlorinated (PCB)
Determination of PCB Content in Transformer Oil Through Gas Chromatography
The Quantitative Analysis of PCB by gas chromatography to identify the PCB (ASKAREL) in transformer oil using the ASTM D-4059 method performed by injecting the sample into the Gas Chromatograph, and the PCB concentration in parts per million (ppm) is precise.

Process (According to current regulations of the Ministry of Environment):

  • Sampling. ID.
  • Geographic Location of the equipment.
  • Quantitative PCB characterization.
  • Classification in groups for the PCB inventory.
  • Inventory of PCBs – regulatory compliance.
  • Marking of equipment and waste.
  • Storage of equipment and waste (owner of the equipment).
  • Transportation, in the national territory of equipment and waste (by the owner).
  • Final Provision and Environmental Appropriateness (performs by the equipment’s owner).
Qualitative PCB'S Analysis

The PCB test kits – CLOR-N-OIL Model 50 ppm, allow qualitatively to determine the content of Polychlorinated Biphenyls (PCB) according to EPA Standard SW-846 Method 9079, for transformer oils.
The Kit contains all the equipment necessary to run the test. The Standard considers an oil
contaminated with PCBs if it has a concentration equal to or greater than 50 ppm.

Furan Content Analysis

Content of Furan Compounds in Transformer Oils

The Furan Content Analysis (2-furfural, furfuryl alcohol, five (5) hydroxymethylfurfural, five (5) methylfurfural) allows determining the deterioration of the insulating paper by the thermal compromise of the same. It also suggests that the remaining useful life of the transformer also complements the chromatography very well of gases in terms of carbon dioxide and carbon monoxide (CO2 and CO).
It is recommended for transformers with more than 12 years of operation.
Knowing that the useful life of the insulation paper is equal to the useful life of the transformer, we can, by an indirect method, estimate the Degree of Polymerization of the insulating paper and, consequently, the useful life of the transformer. 

Special Tests for Dielectric Oil Transformers

Complimentary Analysis of Transformer Oil Degradation.

Complementary tests serve to know the content of additives and or additional properties to those of degradation of the oil.

Power factor (at 25 ° C and 100 ° C)

It measures the possible existence of polar compounds or possible leakage paths of currents in the oil and, therefore, the insulating quality thereof.

Degree of polymerization

It allows us to determine the number of glucose molecules that there is for each cellulose molecule; it will enable us to know the remaining useful life of the insulating paper and, therefore, the estimated useful life of the transformer.

Corrosive sulfur

This test detects the presence of incredible amounts of sulfur compounds in the insulating oil. When these types of compounds are present, they cause corrosion of some metals such as copper and silver.