Transformer Oil Testing and Analysis

Oil filled electric power transformers require periodic maintenance and servicing.  The transformer has two different types of insulation.  Solid insulation and liquid insulation.  The modern transformer is completely dependent on the quality and performance of its both is solid and liquid insulation. The solid insulation is essentially the heart of the transformer and the liquid insulation is the lifeblood of the transformer.  Without the solid and liquid insulation working together, the transformer will fail and electric power to your customers will most likely be disrupted. The solid insulation is made up of fiber press-boards and kraft paper that separates the copper windings and provides insulation and dielectric clearance between copper conductors.  The liquid insulation is comprised of highly refined mineral oils specifically blended for its density, viscosity, and its dielectric qualities to further insulate the transformer’s copper core and windings. The insulating oil serves several purposes such as cooling the core and preventing unwanted and harmful contaminants from damaging the solid insulation.  Additionally, the insulating oil serves as a diagnostic tool in determining the condition of the oil, the condition of the solid insulation and when preventive maintenance and servicing needs to be performed. The most basic way for the transformer operator to check the health of his transformer is to look to the color of the oil.  If the oil is clear and free from visible particulate matter, the oil is most likely still in serviceable condition.  If the oil has become dark red, dark orange, or black, it indicates a high level of acid and other unwanted contaminants present in the oil. Rather than simply using the oil’s color as an indicator of condition, today it is best to use an oil testing and analysis program for determining the specific condition of the solid and liquid insulation. Starting between the seven and eight year mark of continuous transformer service, an annual oil sample must be taken and analyzed.  A good oil analysis program will be able to diagnose the used insulating oil for the following performance characteristics:
  • acid neutralization number
  • dielectric strength
  • moisture content in parts per million (ppm)
  • breakdown voltage
  • particulate matter content in microns
  • interfacial tension
  • gas content
  • dielectric loss tangent (Tan Delta)
All of the above listed parameters are important in determining the health and condition of your transformer’s insulation, but the “Acid Number” is the best indicator of when it is time to service the liquid insulation. When the “Acid Number” reaches 0.08, it is time to process the oil.  Once the acid number exceeds 0.08, the oil will start to become very aggressive against the solid insulation and begin to cause damage. Some electric transmission companies still use a time based preventive maintenance program.  Although it is better than no preventive maintenance program, a time based program may be performed too early or too late.  In either case, both time, labor and money will not be used efficiently and could create a more expensive corrective maintenance situation for your company. A periodic oil analysis monitoring program will allow the transformer operator to perform the preventive maintenance service not too early and not too late, but just at the right time.  This will save, time, labor and money and the operator can direct his maintenance efforts where they are needed most. Oil analysis and the GlobeCore Process, two things your electric power transformers cannot live without!  It’s time to get with the Process.  The GlobeCore Process!

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