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For many years traditional design of liquid-immersed transformers has been based on the combination of cellulose solid insulation and mineral oil. As a result, average temperature rise for windings is normally limited to 65 K, and top oil rise to 60 K as given in IEC 60076-2. Sometimes space or weight limitations or high ambient temperatures force designers to look for new solutions such as those...
The increasing use of non-linear and solid-state based loads has caused an increase in the power system harmonic level. An increase in harmonic level causes the increase in power loss and hot spot temperature of power transformers. Hot spot temperature rise will lead to some insulation aging. Then, considering that the hot-spot temperature is the key limiting factor in transformers loading, the effect...
Transformers are the largest part of the investments of transmission and distribution systems and have a considerable economic impact on the operation of an electrical network. It is advisable to know the insulation condition, operating life, and loading capacitance of transformer to ensure its economical operation and secured service. The most important parameter in transformers life expectancy is...
In order to compare the characteristics of natural ester impregnated Kraft paper and thermally upgraded paper, sealed aging vessels containing copper, insulation paper (Kraft paper and thermally upgraded paper), and natural ester were aged at 90, 110, and 130degC about 400 days. The results show that both degree of polymerization (DP) and leveling-off degree of polymerization (LODP) for thermally...
Insulating system of power transformers is mostly composed of two basic components: insulation oil and cellulose paper (oil-paper system). These components are of an organic nature and thatpsilas why they become very sensitive to operation degradation conditions (temperature, oxidation, moisture etc.). Aging of these components can endanger the failure free operation of the transformers. The main...
Transformer life depends on the life of the oil impregnated paper insulation system. Degradation of the cellulose insulation is an irreversible process. Chemical reaction of cellulose cause opening of glucose rings providing free glucose molecules, water, CO2 and organic acids. These glucose monomers further decompose and produce furanic compounds as end products. DP and furan tests are used to identify...
The life of a transformer is limited to the deterioration of its solid insulation. Winding conductors and other solid insulation materials in oil-immersed transformers have been insulated using cellulose products. For many years, manufacturers have met the needs of special applications by designing transformers using thermally upgraded materials to achieve lighter weight, higher power density and...
This paper describes the electrical characteristics of insulating oil employed in pole transformers. In the experiment, temperature and frequency were selected as variables, and dielectric characteristic values such as the relative permittivity, the tandelta and the specific resistance of the insulating oil were measured by a WinDETA system. As a result, the dielectric characteristics of the testing...
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