Experiences with detection of transformer failure based on insulating oil tests

Comparative Analysis of the Results of Diagnostic Measurements with an Internal Inspection of Oil-Filled Power Transformers

“…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]. It is carried out for the de-energized transformer and with the terminals disconnected from the network.…”

“…It should also be understood that, in addition to the technical condition of the transformer, decision about its de-energizing might be forced by the age of the transformer, its service condition, place of installation, and the ability to replace it by a reserve unit. The proper selection of a diagnostic procedure and correct interpretation of the results obtained from different types of measurements are valid, no matter the place of the transformer installation [3][4][5][6][7][8][9][10][11][12][13][14]. In the case of wind and solar farms, appropriate procedures become even more important due to the accumulation of stresses that affect stresses result, among others, from a high variability of loads, frequent de-energizing of transformers, environmental impact (lightning, large daily fluctuations in ambient temperature, and sea climate), and requirements to stay operational during significant voltage dips [15].…”

“…The best option seems to be the use of methods that are non-invasive, easy to apply, and give an intuitive view about the initial selection of transformers on healthy units and units with suspected or developed defect [5,10,[16][17][18][19]. Among these methods, one of the most important is the analysis of the gases dissolved in oil (DGA), which constitutes a part of the fundamental measurements within the first level of a diagnostic procedure of a transformer in service [9]. DGA is a commonly used method that allows for the detection of thermal or electrical defects that occur in oil-paper insulation.…”

“…With an increase in temperature, hydrocarbons are generated in the following sequence, methane-ethane-ethylene-acetylene, but H2 concentration is low in this case. Thermal decomposition of cellulose is associated with the generation of large amounts of carbon monoxide and lesser amounts of carbon dioxide [4,5,9,13,[16][17][18][19][20]. The conclusions about the transformer's technical condition, based on the results of the chromatographic analysis of the oil sample taken from the transformer, is typically carried out in accordance with the general scheme presented in Figure 1 [20].…”

“…However, it is important to point out that the differences might be a result of the methods applied for determining the nature of the defect. This is especially apparent when the availability of historical measurement data is limited [9,[16][17][18]21].…”