Abstract
This article presents a description of four independent case studies concerning situations when power transformers were directed to internal inspection. This inspection was the result of a specific case of a routine diagnostic procedure that was carried out and, where the transformer was switched off by a Buchholz gas relay. The case studies described were selected such that they represented situations when availability of historical data on the previous measurements was limited and a quick diagnosis had to be made on the basis of the results from the last measurement. In all of the cases presented here, the analysis of the gases dissolved in oil had played an important role in the detection of the defects that turned out to be dangerous for further exploitation of the transformers considered. The first signal about a possible developing defect was elicited solely from the measurements of the oil samples taken from the transformer in service. However, more detailed recognition and initial localization of the defect was possible after additional supplementary measurements (winding resistance, sweep frequency response analysis, etc.), which required the transformer to be switched off. The conducted sequence of actions, based on the developed diagnostic procedure, indicated the possibility of effective and early withdrawal of the transformer from operation, before it underwent a serious failure.
Highlights
Each unexpected outage of power transformer is associated with financial losses for its owner, as well as the energy consumers who are supplied through this transformer
A quantity considered in the assessment of the technical condition of transformers is the winding resistance measurement, which belongs to the fundamental electrical measurements and is performed typically when the first level of diagnostic procedure gives information of the potential defect [9]
During the exploitation of the three winding network power transformers with a rated power of 40/20/20 MVA, a voltage ratio of 115/16.5/16.5 kV, and the vector group YNd11d11 manufactured of 40/20/20 MVA, a voltage ratio of 115/16.5/16.5 kV, and the vector group YNd11d11 manufactured in 1985, the complex measurements were performed in accordance to the diagnostic system in 1985, the complex measurements were performed in accordance to the diagnostic system applied applied in the distribution company [9]
Summary
Each unexpected outage of power transformer is associated with financial losses for its owner, as well as the energy consumers who are supplied through this transformer. On the basis of a proper diagnostic procedure, an effective and rational decision for the further exploitation of a given transformer unit might be made up One of such decisions is timely de-energizing power transformers from service and forwarding it to an internal inspection. In the case of wind and solar farms, appropriate procedures become even more important due to the accumulation of stresses that affect Both the insulation and anothers, active part of transformer. Diagnostic procedures methods must be and chosen, in order to allow the detection of in order to allow the detection of defects occurring solely in these parts of the transformer. DGA is a commonly used method that allows for the detection of for the detection of thermal or electrical defects that occur in oil–paper insulation. Thermal decomposition of cellulose is associated with the generation of large amounts low in this case.
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