Transformer Oil Analysis And Fluid Testing

Transformer Oil Testing is Essential to Every Power Systems’ Health

Transformer oil has excellent electrical insulation and is stable at high temperatures. The oil is used for the purpose of insulation, and discharge stoppage and it acts as a cooling agent for the transformer itself. With the critical use of oil, it is important to do ongoing analysis and oil testing as your transformer is deserving of the best upkeep and servicing!


The condition of the oil can clue you into the health of your transformer. The oil should be tested at least ONCE A YEAR and in addition to repairs, should be a large part of your electrical maintenance plan. RESA Power Oil Testing Laboratory sample turnaround time is THE BEST in the industry!

Timely transformer oil testing also helps to rule out the possibility of degradation. Degraded transformer oil can cause transformer failure. The most common signs of degradation are an increase in acidity and/or water content. An increase in either of these could lead to partial or total discharges within the transformer. In addition, if there is evidence of metal contamination, this could also lead to transformer failure.

On your site or in our shop, the NETA-certified technicians at RESA Power will work to ensure the reliability and integrity of your transformers and electrical equipment through ongoing testing and analysis. Our laboratory offers a full range of transformer oil tests in accordance with ASTM Standard Test Procedures and diagnostic recommendations that are based on IEEE Standard guidelines.


  • Oil Quality
  • Water Content
  • Dissolved Gas Analysis (DGA)
  • Inhibitor Content
  • Furan Test
  • Resistivity Test
  • Corrosive Sulfur
  • Particle Count
  • PCB Analysis of Insulating Fluid
  • Dissolved Metals Test
  • Liquid Power Factor at 25°C & 100°C


  • On-Site Fluid Sampling & Inspection Services
  • Repairs: Tap Changers, Gauges, Radiators
  • Valves, Bushings, Etc.
  • Minor Internal Repairs
  • Electrical Testing
  • De-energized Insulator Cleaning
  • Leak Repairs & Clean-up
  • Painting / Repainting
  • Nitrogen Pressurizing Service
  • Safe-TTR™ Sampling Enclosure
  • NFPA 70E Solutions
  • Load Tap Changer Services


  • Hot Oil Reconditioning
  • De-gasification of Oil
  • Dehydration of Oil
  • Standard Oil Filtering
  • Vacuum Filling
  • Retrofill with New Oil
  • Inhibi-TTR™ Inhibitor Injection
  • Passiv8-TTR™ – Corrosive Sulfur
  • Other Fluid Services

RESA Power Transformer Oil Testing Laboratory

The RESA Power’s transformer oil lab receives the samples and analysis in a couple of key ways. Our Oil Testing Laboratory located in California offers a full range of transformer oil tests in accordance with ASTM Standard Test Procedures and diagnostic recommendations that are based on IEEE Standard guidelines.

Our experts typically perform a standard screen test which includes:

  • ASTM D1533: Moisture test to measure water content in insulating fluid.
  • ASTM D1816 & ASTM D877: Dielectric breakdown test is to measure the voltage at which the insulating fluid begins to conduct.
  • ASTM D974: Acid test measures the content of acids formed in the insulating fluid by oxidation process.
  • ASTM D1500: Color test monitors the darkening of the fluid which is an indication of fluid deterioration.
  • ASTM D971: IFT test measures impurities in the transformer insulating fluid including the presence of polar contaminants.
  • ASTM D924: Power Factor test measures dielectric losses in an electrically-insulating liquid.
  • ASTM D2668: Oxidation inhibitor test measures the amount of inhibitor content remaining after oxidation has reduced the inhibitor level. Inhibitors in the fluid will increase the service life of the fluid.

RESA Power offers cost-effective Transformer Oil Testing and Fluid Maintenance include:

  • Dehydration and filtration of smaller indoor transformers
  • Dehydration
  • Degas
  • Vacuum Oil Filling
  • Oil Reclamation using Fullers Earth
  • Retrofill Services from Mineral to FR3

Transformer Fluid Testing and Maintenance

Regular transformer oil testing and maintenance are essential to keeping your equipment running smoothly and reducing the risk of costly repairs. RESA Power’s cost-effective services include dehydration and filtration of smaller indoor transformers, degas, vacuum oil filling, and oil reclamation using Fullers Earth. We also offer retrofill services from mineral to FR3. Our experienced technicians will work with you and recommend the transformer oil testing and maintenance plans that best fit your needs and budget.

RESA Power’s technicians are trained to provide safe and careful on-site sampling services, using industry recognized methods to ensure the integrity of the dielectric fluid sample. The samples are carefully packaged and shipped to a RESA fluid testing laboratory.

RESA Power’s technical experts will also perform a thorough inspection of your transformer to identify potential issues, to include gauges, wiring, connectors, fluid levels, verify nameplate data, check for rust, leaks, and abnormal wear, and also collect important photographs of the inspection.

Fluid sampling is dispatched and performed by many RESA Power facilities around the U.S., and is universally accepted as required key component of proper transformer maintenance.


The insulating fluid in a power transformer performs two major functions:

  • Serves as electrical insulation to withstand the high voltages inside the transformer.
  • Acts as a heat transfer medium to carry out heat generated within the transformer windings.

Transformer oil analysis is a cost-effective electrical preventive maintenance tool. RESA Power and transformer manufacturers recommend an annual transformer fluid testing routine. Dielectric fluid testing provides reference points that can show a historical trend in the fluid condition. Quantitative transformer oil analysis can indicate the priority of taking preventive maintenance action.

As a transformer ages, gases and contaminants can dissolve in its fluid and lead to transformer failure. Sampling and analysis of the transformer oil form the cornerstone of transformer preventative maintenance.

Other RESA Power Transformer Fluid Services Include:

  • Filtration and Dehydration
  • De-gassing
  • Vacuum Oil Filling
  • Oil Reclamation with Fuller’s Earth
  • Retrofill Services with FR3 Natural Ester Fluid
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Every transformer needs periodic maintenance, oil testing, and analysis to determine any potential problems, before a transformer’s performance is compromised. Dissolved Gas Analysis (DGA) transformer oil testing is considered to be the best method for determining a transformer’s overall condition. RESA Power’s highly skilled technicians have expertise in the DGA universal standard of oil testing.

Benefits of DGA

Regular testing and DGA analysis of transformer oil are critical to the ongoing maintenance and support of a transformer’s health. DGA testing has the following advantages:

  • Advanced warning of developing faults;
  • Status checks on news and repaired units;
  • Convenient scheduling of repairs;
  • Monitoring of units under potential overload conditions.
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Leave it to the Professionals

DGAs should be conducted by a trained professional, like RESA Power’s NETA-certified technicians. Our experts will assist in recognizing issues on both new and older power components and systems, which include for example (but are not limited to):

  • Rate of gas production – A sudden increase in key gases (such as hydrogen or Acetylene). Note: the rate of increased gas production is more important in evaluating a transformer than the amount of gas
  • Thermal fault – The generation of any amount of gas in ppm indicates high energy arcing and can possibly generate a very hot thermal fault (1000 degrees Celsius)
  • Acetylene levels – Determination of the level of acetylene in the transformer. For example, if acetylene is generated by internal arcing, sampling should be taken weekly to determine if there is an additional generation of If no additional acetylene is found and the level is within the accepted IEEE standard, the transformer may continue in service. If, however, there is an increase of acetylene levels, the transformer has an internal arc and should be taken out of service. This is because operating a transformer with a high amount of acetylene is extremely hazardous.

RESA Power respects the delicate balance between systems and supportive testing. Our transformer oil testing and analysis services are designed so that you can trust working with the experts at RESA Power. Your critical transformer preventative maintenance needs ensures the safety of your team and the reliability of your equipment.

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Physical, Chemical, and Electrical Dielectric Fluid Quality

RESA Power is uniquely capable of addressing the most critical requirements of power systems’ reliability, operability, and efficiency. Part of this holistic approach to power maintenance includes the consideration of specific properties or parameters of insulating oil for transformer oil testing. These properties of transformer oil include electrical, chemical, and physical aspects. All need to be analyzed and tested for quality.

Electrical properties include: dielectric strength, gassing tendency, and dielectric dissipation factor (or power factor).

Chemical properties include: water content, acidity, and sludge content.

Physical properties include: interfacial tension, viscosity, flash point, and pour point.

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Diagnostic Testing for Transformer Fitness

Customers that incorporate RESA Power’s electrical, chemical and physical transformer oil testing avoid unscheduled maintenance and repair costs. Let RESA Power ensure your transformers are fit for compliance standards and meet safety guidelines that will provide you with peace of mind.

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Electrical Dielectric Diagnosis

When testing electrical properties RESA Power, NETA technicians utilize diagnostic methods that measure dielectric levels. These tests provide crucial evidence of changes in the condition of the insulation. The results and tracking of this critical data increase the longevity of the transformer and prevent system failures.

RESA Power utilizes dielectric testing to test a transformer’s reaction, duration and breakdown during an analysis using voltage rates. We test the durability of the insulating barrier materials in transformers while analyzing the resistance to various harmful voltage levels. Results are not only important to safeguarding material damage, but also important to reducing injuries due to faulty equipment.

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Chemical Testing

Water, gas, and particles in the transformer’s insulation system will negatively impact the transformer’s longevity. These are tested thoroughly by RESA Power to reduce damage and limit equipment downtime.

Moisture or water content in transformer oil is highly undesirable, affecting the dielectric properties of the oil adversely. Water content in oil also affects the paper insulation of the core and winding of a transformer. Another chemical property that can affect transformer performance is acidity: if transformer oil becomes acidic, the water content in the oil becomes more soluble, deteriorating the insulation properties of the paper as it is winding. Acidity can also accelerate the oxidation process and the rusting of iron in the presence of moisture

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Physical Fitness Analysis

The physical properties of transformer oil are analyzed by RESA Power with a focus on the following elements: interfacial tension, flash point, pour point, and viscosity.

In general, good-quality, new oil generally exhibits high interfacial tension. It is also desirable to have a very high flash point; over 145 degrees is considered acceptable. The best pour point is the minimum temperature at which oil starts to flow under standard test conditions. Therefore, higher pour points are desirable in colder temperatures, but it also depends upon the type of oil being used (e.g. Paraffin-based oil necessitates higher pouring temperatures than Naphtha-based oils).

By analyzing the physical properties of transformer oil, RESA Power can ensure that the transformer is operating properly and identify any issues that may be affecting its performance. Additionally, by monitoring these properties over time, we can detect early signs of deterioration that may lead to transformer failure. In short, transformer oil testing is an essential part of maintaining a safe and reliable electrical system.

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