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Dissolved gas analysis (DGA) interpretation
Enter the lab result for a mineral-oil transformer: the dashboard gives you the IEEE C57.104-2019 DGA status, the probable fault type on the Duval triangles and from the IEC 60599 ratios, and warns you if the gases rose more than normal since the previous sample.
IEEE C57.104-2019§ 6.1.3DGA status, Tables 1 to 4IEEE C57.104-2019§ 6.2.3Duval triangle 1IEEE C57.104-2019§ D.4Duval triangles 4 and 5IEC 60599:2022§ 5.4basic gas ratios
Results
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Charts
- Current sample
- Previous sample
- Current sample
- Above Table 2
- Between Tables 1 and 2
- Below Table 1
- Table 1 (×1) and Table 2
Calculation and details
Step-by-step calculation
What it means for your transformer
What it is for
Dissolved gas analysis (DGA) is the test that gives the earliest warning of an internal fault in an oil-filled transformer: a hot spot, a loose connection, partial discharges or an arc leave their gas signature long before a protective relay operates. The lab report gives seven or eight concentrations in ppm, and reading it properly means cross-checking several tables and methods. This tool does that cross-check with the IEEE C57.104-2019 guide and with IEC 60599, so you know whether the result calls for a confirmation sample, closer monitoring or electrical tests, and which type of fault is the most likely.
How it is calculated
IEEE C57.104-2019§ 6.1.3Tables 1 to 4
DGA status
Status 3 if any gas > Table 2 · Status 2 if any gas > Table 1 · Status 1 otherwiseTables 1 and 2 are the 90th and 95th percentiles of a large database of lab results, split by the O2/N2 ratio (≤ 0.2 or > 0.2) and the transformer age. Without O2/N2 the > 0.2 section is used, as step 3 of the procedure states. With a previous sample, each increase Δ = Ccurrent − Cprevious is compared with Table 3 (for acetylene, any increase): if it exceeds it, the guide calls for a confirmation sample before changing the status (step 4b). An ethylene increase of 200 ppm or ethane of 1000 ppm is treated as an extreme result (6.1.2.4).
IEEE C57.104-2019Table 4, rates from 3 to 6 samples
Rate = Δ · 365 / days [ppm/year]Table 4 was derived by linear regression over 3 to 6 samples in 4 to 24 months. With two samples the rate is only indicative: the tool compares it with Table 4 when the interval falls in 4–9 or 10–24 months, but does not raise the status because of it.
IEEE C57.104-2019§ 6.2.3Table 6IEEE C57.104-2019§ D.4Tables D.3 and D.4
Duval triangles
%CH4 = 100 · CH4 / (CH4 + C2H4 + C2H2) · likewise for C2H4 and C2H2The three percentages place the point on triangle 1 and the zone comes from the limits of Table 6: PD with CH4 ≥ 98 %; T1, T2 and T3 with C2H2 < 4 % (15 % for T3) and C2H4 below 20 %, between 20 and 50 % or above 50 %; D1 with C2H4 < 23 % and C2H2 ≥ 13 %; D2 and DT elsewhere. Triangle 4 uses H2, CH4 and C2H6 and triangle 5 uses CH4, C2H4 and C2H6, with zones S (stray gassing), O (overheating < 250 °C), C (possible paper carbonization), T2, T3 and ND (not defined). In two rows of Tables D.3 and D.4 the printed text does not match Figures D.3 and D.4 and leaves zones unassigned; the tool follows the figures, and the tests check it point by point.
IEC 60599:2022§ 5.4Table 1, ratio interpretation
R1 = C2H2/C2H4 · R2 = CH4/H2 · R3 = C2H4/C2H6- PD: R2 < 0.1 and R3 < 0.2 (R1 not significant).
- D1: R1 > 1; R2 from 0.1 to 0.5; R3 > 1. D2: R1 from 0.6 to 2.5; R2 from 0.1 to 1; R3 > 2.
- T1: R3 < 1 (R1 and R2 not significant). T2: R1 < 0.1; R2 > 1; R3 from 1 to 4. T3: R1 < 0.2; R2 > 1; R3 > 4.
IEC 60599 no longer uses the 0, 1 and 2 codes of the old IEC 599: it compares the ratios with these ranges. A combination that falls in no row has no diagnosis, and D1 and D2 overlap when R1 is between 1 and 2.5. A gas absent from both numerator and denominator (0/0) is taken as a zero ratio.
IEEE C57.104-2019§ D.8CO y CO2IEC 60599:2022§ 5.5CO2/CO ratio
CO2/CO < 3 with CO > 1000 ppm · CO2/CO > 20 with CO2 > 10,000 ppmHigh CO with a low ratio only points to the paper if there are also significant hydrocarbons; without them it is usually oil oxidation with little oxygen. High CO2 with a high ratio indicates slow paper aging, which is confirmed with furans.
Limits of the calculation
- It is an indicative interpretation, not a diagnosis. The values in the IEEE tables are statistical: the guide itself warns that they are not universal limits and that each transformer owner should derive its own from its history.
- It applies to mineral-oil power transformers. It does not apply to natural or synthetic esters (IEEE C57.155), to the on-load tap changer compartment, or to instrument transformers or bushings.
- With every gas below Table 1, IEEE C57.104 does not recommend identifying the fault: the point on the triangles is shown for reference only.
- If the on-load tap changer leaks oil into the main tank, acetylene and ethylene can rise without a fault in the active part.
- The triangles and the ratios always point to a zone, whether there is a fault or not. Confirm with a second sample taken in a syringe and with electrical tests before deciding on an intervention.
Frequently asked questions
How is the dissolved gas analysis of a transformer interpreted?
In two steps. First, decide whether there is anything to investigate: IEEE C57.104-2019 compares each gas with its 90th and 95th percentile values for the O2/N2 ratio and the transformer age, and the increase from the previous sample, and assigns a DGA status from 1 to 3. Only if a gas exceeds those values is the fault type identified with Duval triangle 1 (and triangles 4 and 5 to refine thermal faults) or with the IEC 60599 ratios. With all gases low, the guide does not recommend a diagnosis.
What does acetylene in transformer oil indicate?
Acetylene (C2H2) forms in significant amounts near 1000 °C, in arcs and sparks or in very hot spots. A transformer without internal fuses, switches or other arcing parts should not produce it in normal service. That is why IEEE C57.104-2019 treats any increase of acetylene between two samples as a change to be confirmed and sets for it the lowest reference values of all the gases, from 1 to 7 ppm depending on the case.
How is the Duval triangle used?
Add up the methane, ethylene and acetylene concentrations and calculate the percentage of each over that sum. Those three percentages are the coordinates of a point on the triangle, which falls in one of seven zones: PD (partial discharges), D1 and D2 (low- and high-energy discharges), T1, T2 and T3 (thermal faults below 300 °C, between 300 and 700 °C and above 700 °C) and DT (mixed). If the result is PD, T1 or T2 it can be refined with triangle 4 (hydrogen, methane and ethane); if it is T2 or T3, with triangle 5 (methane, ethylene and ethane).
We test your transformer when the oil gives a warning
If DGA rises, electrical tests locate the fault: we measure turns ratio, winding resistance, insulation, %Z and tan δ on medium-voltage, high-voltage and extra-high-voltage transformers in substations and industry, in Colombia, or elsewhere on request.