The article describes selected graphical methods (Duval triangle, Duval pentagon and Mansour pentagon), which may be used for the analysis of gases dissolved in oil of power transformers. The effectiveness of recognizing the basic types of defects by these methods was assessed. This is of significant importance for the services responsible for maintaining transformers in operation.
Słowa kluczowe: power transformer, oil-paper insulation, diagnostics, DGA
W artykule opisano wybrane metody graficzne (trójkąta i pięciokąta Duvala oraz pięciokąta Mansoura), które można stosować do analizy gazów rozpuszczonych w oleju transformatorów energetycznych. Oceniono skuteczność rozpoznawania przez te metody podstawowych typów defektów. Ma to istotne znaczenie dla służb odpowiedzialnych za utrzymanie transformatorów w ruchu.
Keywords: transformator energetyczny, izolacja papierowo-olejowa, diagnostyka, DGA
Oil-paper insulation, typically used in the power transformer, both during normal operation and during electrical or thermal disturbances decomposes. During this process, gases are generated (H2 - hydrogen, CH4 - methane, C2H6 - ethane, C2H4 - ethylene, C2H2 - acetylene, CO - carbon monoxide and CO2 - carbon dioxide) which partially remain dissolved in the oil. Experience shows that the amount and composition of gases dissolved in oil allows to conclude about the occurrence of a defect in the transformer and its type. General information on the decomposition product of the oil insulation formed during different types of fault are given in Table 1. If the defect comprises the cellulose insulation carbon monoxide and carbon dioxide are also appear. Since taking an oil sample from a working transformer and then determining the type and amount of dissolved gases is a simple and cheap procedure, their analysis (marked with the acronym DGA) is the basic method of diagnosing the technical condition of the transformer. Tab. 1. Decomposition product of the oil insulation formed during different types of fault [1, 2] Fault type Gases Partial discharges H2, CH4 (C2H4, C2H6) Discharges H2, C2H2 (CH4, C2H4) Thermal faults CH4, C2H6, C2H4, H2 In parentheses are given the gases associated in small quantities. On the occurrence of a defect, one concludes by comparing the currently measured values of gas concentrations with typical values. Typical values are determined on the basis of statistical analysis of gases dissolved in oil of transformer groups with common characteristics (e.g. on-load tap-changer). The intensity of the defect can be assessed to a certain extent by comparing the changes in gas concentration values between consecutive measurements with the typical values of such changes. Typical values of changes in gas concentrations over time are also determined for similar groups of transformers using statistical analysis. An [...]
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