Analysis of tap changers damageability and technical condition evaluation by DGA

Summary

The article includes the detailed damaging (both defects, which were found by operating staff, and failures) analysis of tap changers and its units: selector switch, diverter switch and drive. There have been investigated the type and location of defects, reasons and initiators of defect appearance, the influence of operation life and tap changers (TC) construction features on the damaging. The efficiency of different measurement types of tap changers defect detection is evaluated on the data in addition to the analysis of TC reliability. Next the article considers the capabilities and improvements of diverter switch condition control by DGA. On the basis of dispersion analysis is shown the influence degree of number TC switchers, transformer load capacity and TC operation life on the maximum permissible value (MPV) of DGA. As the result the authors advise using criterion of exceeding MPV of DGA content for diverter switch accounting these factors. There are given recommendations on defect identification in diverter switch in gas ratios accounting authenticity of gas pair relations. Then we examine the character detection experience of defect developing in TC selector switch by DGA. We should note that MPV DGA for accuracy evaluation of technical condition of in-tank selector switch must be differentiated with respect to the type of oil protection and oil grades, operation life and PT power class. Authors show the own procedure of defect identification by DGA that has two advantages: it does not have unrecognizable conditions; it allows detecting defect combinations of heat and electrical nature with different level of development. The article demonstrates examples showing the proposed procedures of defect identification by DGA results for diverter and selector switch that have the defects as the result of TC unsealing.

Additional informations

Authors

Elben Andreas, Rasch Matthias, Mohaupt Peter