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Transformer Oil Dielectric Strength

Transformer Oil Dielectric Strength

How to comprehensively measure the electrical performance of insulating oil in terms of dielectric strength, dielectric loss and volume resistance?


An important role of insulating oil is to insulate oil-filled electrical equipment to ensure safe operation under high insulation. Dielectric strength, dielectric loss and volume resistivity are the main parameters that indicate the electrical performance of the insulating oil. In general, they can reflect the insulating oil by impurities, water contamination or oil degradation, but they have different emphasis.

Generally speaking: insulation strength and volume resistivity test are more convenient, but the accuracy of insulation strength is not as high as volume resistivity; dielectric loss including polarization loss and conductivity loss, and volume conductivity only reflects the conductivity loss, so tanδ is more comprehensive than ρv  to reflect the insulation, deterioration and moisture condition of the oil, but measuring ρv  is simpler than measuring tanδ. Therefore, more and more countries begin to apply the measurement of ρv  to assess the quality of oil.


As far as our country is concerned, it should be decided according to the production requirements and test conditions. For example, if the test is done in the field and the result is immediate, the insulation strength test can be done; if the sample is taken back to do the test, it is best to do tanδ if there are conditions, and if there are no conditions, it can be done as ρv  or E. For some oils, several items have to be done according to the production needs. If E and ρv  are qualified, but tanδ is unqualified is a normal phenomenon, that is, we should strengthen the treatment of polar substances; if only E is qualified, ρv  and tanδ are unqualified is also normal, and we should strengthen the oil treatment. On the contrary, if tanδ is qualified, but ρv  and E are unqualified, or tanδ and ρv  are qualified, but E is unqualified, it is necessary to analyze the specific situation. For example, it is a test problem or sampling problem, etc., can not be generalized.


At present, the test instrument, more and more advanced, convenient, if possible, the best for important equipment oil, so that from all aspects to determine the electrical properties of the oil is more reliable, but also the purification of the oil more guiding role in the treatment.

PureTech Oil Filtration always manufactures and supplies the top-quality transformer oil treatment machines, which includes Transformer Oil Filtration Machines (Vacuum Oil Purifier) and Transformer Oil Regeneration plant (for deteriorated transformer oil treatment), we aim to support you with tailored solutions for your transformer oil treatment, and help you to save the maintenance cost.

More information about our oil filtration machine, please contact us freely.