The analytical services performed by Doble’s Materials Laboratories provide you with the accurate information you need to intelligently diagnose any existing and potentially devastating problems in your liquid-filled equipment. Compared with the cost of premature or catastrophic failure, regularly scheduled oil testing is a cost-effective and sound maintenance practice that is used to extend the life of your transformers and circuit breakers. Doble Laboratory can provide paper and oil testing in the areas listed below.
For more information, please contact the Doble Laboratory Business Office at firstname.lastname@example.org.
Dissolved Gas Analysis
Dissolved Gas Analysis is the single most important test performed on oils from transformers. As the insulating materials in a transformer break down due to thermal and electrical stresses, gaseous byproducts are formed. The byproducts are characteristic of the type of incipient-fault condition.
Furanic Compounds In Oil
As the cellulosic insulation in a transformer ages, oil-soluble byproducts of the cellulose chain called furanic compounds are produced. High concentrations of 2-furfural, the predominant compound, are a clear indication of cellulose degradation, as this is the only type of material in transformers that yields this byproduct. When cellulosic materials are exposed to extreme temperatures, which results in charring, furanic compounds can be destroyed and the carbon oxides may be the only byproducts remaining in significant quantities. Experience is required in evaluating the furanic compound data, as there are factors such as type of insulation preservation/oil expansion system, type of conductor wrapped insulation, family of transformer and treatment of the oil or the transformer, which can influence the interpretation. Tests for furanic compounds should be performed initially for all power transformers (to have a baseline), for important or older transformers, when high carbon oxides are generated, for highly loaded transformers and when other tests indicate accelerated aging.
Water in Oil Analysis
The dielectric breakdown voltage of insulating material is a function of the water content. The water migrates between the solid and liquid insulation in a transformer with changes in temperature. The water content is reported in parts per million and percent of relative saturation.
Degree of Polymerization
The degree of polymerization (DP) test is another means for assessing insulation aging. This test is performed on paper samples. The DP test provides an estimate of the average polymer size of the cellulose molecules in materials such as paper and pressboard. Generally, paper in new transformers has a DP of about 1000. Aged paper with a DP of 150-200 has little remaining mechanical strength, therefore making windings more susceptible to mechanical damage during movement, particularly during extreme events such as through-faults. As insulation aging in transformers can be uneven due to thermal, moisture, oxygen and byproduct concentration, gradient samples from various locations are needed to provide the best diagnosis of the overall insulation condition.
DP testing is recommended in these cases:
- There is other evidence of very accelerated aging of the insulation
- The transformer is > 20 years old and an internal investigation is being performed
- For condition assessment of older transformers for possible refurbishment
- When a partial rewind is being considered
- To assess cause of failure
- For condition assessment of insulation when purchasing a service-aged transformer
- To assess the condition of a transformer after an extreme overheating event