Dissolved gas analysis calculator: IEC 60599 ratios and Duval triangle
Enter the chromatograph concentrations and get total combustible gas, IEEE C57.104 levels, the IEC 60599 ratios and the Duval Triangle 1 zone.
IEC 60599 gas ratios and Duval triangle
Enter the chromatograph concentrations in ppm. The tool calculates total combustible gas, the levels of the classic IEEE C57.104 table, the three IEC 60599 ratios and the Duval Triangle 1 zone.
Result
The triangle uses only CH₄, C₂H₄ and C₂H₂, expressed as a percentage of their sum. It always returns a zone, even with gases at noise level: read it only when there is real generation.
The levels are those of the classic IEEE C57.104 table (1991 edition), still the most widely used field reference. The 2019 edition replaces that approach with percentiles by unit type.
Indicative result. The calculation runs in your browser and is not sent to any server. This website may contain errors or omissions: before making any decision about an installation, the information must be checked and validated by a qualified engineer. Legal notice and terms of use
What this calculator does
It takes chromatograph concentrations in ppm and returns four readings of the same analysis: total combustible gas, the level from the classic IEEE C57.104 table, the three IEC 60599 ratios with their diagnosis, and the Duval Triangle 1 zone with the point plotted on the triangle.
Where the gases come from
Each degradation mechanism inside the transformer breaks certain molecules and not others, which is why the gas mixture identifies the fault:
- Hydrogen (H₂): appears with almost everything, and is the first to show in partial discharges.
- Methane and ethane (CH₄, C₂H₆): moderate overheating of the oil.
- Ethylene (C₂H₄): severe overheating, above 300 °C.
- Acetylene (C₂H₂): electrical arcing. It needs temperatures above 700 °C and is produced no other way.
- Carbon monoxide and dioxide (CO, CO₂): degradation of cellulose, that is, of the insulating paper.
IEEE C57.104 levels
The calculator sorts the analysis into four levels using the 1991 edition table, still the most widespread field reference. The level is that of the worst gas, not the average.
| Gas | Level 1 limit (ppm) |
|---|---|
| H₂ | 100 |
| CH₄ | 120 |
| C₂H₆ | 65 |
| C₂H₄ | 50 |
| C₂H₂ | 1 |
| CO | 350 |
| CO₂ | 2,500 |
| Total combustible gas | 720 |
The 2019 edition of IEEE C57.104 replaced this approach with percentiles by unit type and age. It is finer, but it demands information you do not always have to hand; the classic table remains a good first filter.
A high value without context means little: what decides is the generation rate, how much each gas has risen since the previous analysis. A transformer sitting at 600 ppm of hydrogen, stable for five years, is far less worrying than one that has gone from 40 to 120 in three months.
IEC 60599 ratios
The standard uses three quotients — C₂H₂/C₂H₄, CH₄/H₂ and C₂H₄/C₂H₆ — and a table that translates them into six fault types: PD (partial discharges), D1 and D2 (low- and high-energy discharges) and T1, T2 and T3 (thermal faults below 300 °C, between 300 and 700 °C and above 700 °C). When the three ratios match no row, the calculator says so rather than inventing a diagnosis: the standard itself recognises that situation.
Duval Triangle 1
The triangle takes only CH₄, C₂H₄ and C₂H₂, expresses them as a percentage of their sum and places the point on a ternary diagram divided into seven zones. The calculator draws the triangle with its zones and marks the point of your analysis.
Its boundaries are the published ones: 98% CH₄ for PD; 4%, 13%, 15% and 29% C₂H₂; and 20%, 23%, 40% and 50% C₂H₄. Zone DT, between the thermal and the electrical ones, covers mixtures of both mechanisms.
Worked example
Transformer with H₂ 180, CH₄ 95, C₂H₆ 30, C₂H₄ 210, C₂H₂ 4 and CO 320 ppm.
- Total combustible gas: 839 ppm → level 2 on the total, level 3 on ethylene and level 3 on acetylene.
- Ratios: C₂H₂/C₂H₄ = 0.02; CH₄/H₂ = 0.53; C₂H₄/C₂H₆ = 7.0.
- Duval: CH₄ 31%, C₂H₄ 68%, C₂H₂ 1% → zone T3.
Reading: a thermal fault above 700 °C, with enough acetylene to warrant close watching. The usual suspects are a poor internal connection or circulating current in the core.
What this calculator does not do
It does not know the history, so it calculates no generation rates — and that is the figure that really decides. It does not know whether the transformer has its tap changer in the same oil volume, which explains perfectly normal acetylene readings, nor whether the sample was properly taken, nor whether the unit has recently been back in service after a repair. And it does not cover Duval triangles 4 and 5 or the Duval pentagon, which refine the diagnosis on low-temperature faults.
What measures it
The analysis is run by a laboratory from an oil sample, or by a dielectric oil analyser on site. For critical units the alternative is on-line monitoring: hydrogen and dissolved gas sensors that flag a change in trend between samples, instead of waiting for the six-monthly analysis. Oil treatment — drying and degassing — is the other half of the job.
Frequently asked questions
- Which gas points to the most serious fault in a transformer?
- Acetylene (C₂H₂). It takes an electrical arc to produce it, so any appreciable amount in a transformer without a tap changer sharing the same oil volume calls for investigation. The level 1 limit in the classic IEEE C57.104 table is 1 ppm: the strictest of all the gases.
- Does the Duval triangle work at low concentrations?
- No. The triangle normalises the three gases to a percentage of their sum, so it always returns a zone even when all three are at the chromatograph’s noise level. First confirm that there is real generation — concentrations above typical values, or an appreciable generation rate — and only then read the zone.
- What is the difference between the IEC 60599 ratios and the Duval triangle?
- The ratios use quotients between pairs of gases and leave gaps: some combinations fall in no row of the table. The triangle always gives an answer because it covers the whole space, which is both an advantage and a risk. The sensible approach is to apply both and to be suspicious when they disagree.