This is not a substitute for expert diagnosis. One sample cannot show a trend. Compare the result with the transformer's own history and with the limits in the equipment specification.
Duval Triangle 1
Rogers ratios
IEEE C57.104 status
Key-gas method
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Methods
Duval Triangle 1. Methane, ethylene, and acetylene are converted to a percent of their sum. The zone is PD, T1, T2, T3, D1, D2, or DT, using the limits published with IEC 60599. The triangle is for identifying a suspected fault. It is not, by itself, proof that a fault exists.
Rogers ratios. CH4/H2, C2H2/C2H4, and C2H4/C2H6 are coded with the IEC 60599 table. A code set that is not in that table is reported as no matching case. A ratio is not formed when both gases in the pair are zero.
IEEE C57.104-2019 status. Each gas is compared with Table 1 (90th percentile) and Table 2 (95th percentile) for the O2/N2 column and age band you select. At or below Table 1 is status 1 on levels. Between the tables is status 2. Above Table 2 is status 3. Tables 3 and 4 need an earlier sample, so they are not applied. A single sample cannot show active gassing. When O2/N2 is unknown, the page uses the column for a ratio at or below 0.2 and says so.
Key-gas method. IEEE C57.104-2019 Annex D.1. The gas with the highest multiple of its Table 1 norm, among acetylene, hydrogen, ethylene, and carbon monoxide, is the key gas when that multiple is above 1. The annex says an automatic reading is often inconclusive.
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