One Map, Clear Division of Labor
Dissolved gas analysis (DGA) is governed by a complementary set of international and national standards. Together they answer three questions: how to measure, how to interpret, and what an online monitor must itself satisfy. The confusion in procurement usually comes from mixing these roles — applying an interpretation standard to a measurement question, or judging an online monitor against a laboratory sampling standard. This article lays out the map, following Chapter 2.6 of the L-PAS DGA whitepaper, and explains what standards compatibility means for an online monitor.
The Global Standards at a Glance
The core framework consists of the IEC, IEEE, and Chinese standards shown below. Each has a distinct role.
| Standard | Version | Role and function |
|---|---|---|
| IEC 60599 | 2022 | Interpretation guide for DGA results; defines fault types PD/D1/D2/T1/T2/T3 and the Duval triangle/pentagon |
| IEC 60567 | 2023 | Sampling and laboratory analysis specification; includes online sampling consistency; total analytical uncertainty ≈ ±15% |
| IEEE C57.104 | 2019 | Interpretation guide for oil-immersed transformers; Condition 1–4 classification and retest intervals; incorporates the Duval pentagon |
| GB/T 7252 | — | Guide for DGA analysis and interpretation in transformer oil (China) |
| DL/T 722 | — | Technical specification for online DGA monitoring devices for power equipment (China) |
| CIGRE TB 296 | — | Technical brochure on recent advances in DGA interpretation methods (reference) |
How to Measure vs How to Interpret
The division of labor is straightforward. IEC 60567 specifies how to measure: sampling, degassing, and laboratory analysis, with the laboratory’s total analytical uncertainty on the order of ±15%. IEC 60599 and IEEE C57.104 specify how to interpret: they translate measured gas concentrations into fault types and condition ratings. IEC 60599 defines the six fault types — partial discharge (PD), low-energy discharge (D1), high-energy discharge (D2), and thermal faults T1 (<300 °C), T2 (300–700 °C), and T3 (>700 °C) — and includes the Duval triangle and pentagon methods. IEEE C57.104 classifies equipment condition into Condition 1–4 with recommended retest intervals. China’s GB/T 7252 provides national interpretation criteria, and DL/T 722 sets the technical specification for online monitors adapted to local conditions. CIGRE Technical Brochures, such as TB 296, provide research reference. For a deeper head-to-head, see our comparison of IEC 60599 and IEEE C57.104.
Condition Ratings and Re-Test Intervals
IEEE C57.104 gives the interpretation layer an actionable structure: four condition ratings, each with a recommended retest interval. The ratings scale from normal operation to an actively developing fault.
- Condition 1 — normal; gases at low levels; annual routine retest
- Condition 2 — caution; gas levels rising but below thresholds; quarterly retest
- Condition 3 — abnormal; approaching or exceeding alarm thresholds; monthly retest
- Condition 4 — severe; thresholds exceeded, developing fault; daily or continuous monitoring
The structure explains why continuous monitoring matters: at Condition 4 the standard itself calls for daily or continuous monitoring, which only an online instrument can provide. Trend data and the gas generation rate — absolute in ppm/day and relative in %/month — are what allow a monitor to compute condition in real time and trigger alarms, compensating for the lag of periodic sampling.
Making an Online Monitor Standards-Compatible
An online monitor should be compatible with this framework at three levels so its results remain comparable and mutually recognized. First, sampling consistency: the oil-gas separation and degassing approach should align with IEC 60567 practice so that online readings agree with laboratory measurements within the same order of uncertainty. Second, calibration traceability: measurements should trace to national metrological standards through regular standard-gas calibration, so that drift does not invalidate long-term trend data. Third, data interfaces: the monitor should expose data in a form the interpretation and asset-management systems can consume — the fault-type taxonomy of IEC 60599, the condition ratings of IEEE C57.104, and protocols such as MODBUS, IEC 61850, IEC 60870-5-104, and DNP3.0. When a monitor satisfies all three, its output can be interpreted by the same diagnostic methods — Duval, ratio, and trend analysis — used for laboratory data anywhere in the world.
PAS DGA for Online DGA Monitoring
PAS DGA’s DGA-900 L-PAS monitor is designed for standards compatibility at all three levels: its oil-gas separation follows IEC 60567-consistent practice, its calibration is traceable to standard gas, and its data integrates via MODBUS, IEC 61850, IEC 60870-5-104, and DNP3.0 for digital-substation use. The underlying photoacoustic spectroscopy technique measures 9 gases plus moisture with a C2H2 detection limit of ≤0.1 ppm, so the data feeds IEC 60599 and IEEE C57.104 interpretation methods directly. For guidance on specifying such a monitor, see our selection framework, and contact PAS DGA to discuss your standards and integration requirements.