IEC 60599:2015

Overview

IEC 60599:2015 provides guidance for interpreting dissolved and free gas analysis (DGA) results from mineral oil‑filled electrical equipment. It explains how concentrations of dissolved gases and free gases can be used to diagnose the condition of oil‑immersed apparatus (for example, power, instrument and distribution transformers, reactors, bushings, switchgear and oil‑filled cables) and to recommend appropriate follow‑up actions. This third edition (2015) is a technical revision of the 1999 edition and Amendment 1:2007, and includes several significant updates to interpretation rules, figures and bibliography.

Key edition changes:

• Revision of multiple clauses (notably 5.5, 6.1–10 and several annex items)
• Addition of a new sub‑clause 4.3
• Expanded bibliography
• Revised Figure 1 and addition of Figure B.4

Key Topics

• Dissolved and free gas mechanisms - origins of gases from oil and cellulosic insulation decomposition, stray gassing and other sources.
• Fault identification - interpretation approaches linking gas signatures to fault types (thermal, electrical/arcing, partial discharge).
• Gas concentration analysis - examination of DGA values, typical concentration levels, alarm thresholds and rates of gas increase.
• Gas ratios and graphical tools - use of basic gas ratios (examples in the standard) and graphical representations such as Duval triangles to classify fault types.
• Application notes - Annex A provides equipment‑specific guidance (transformers, bushings, cables, switchgear) to aid practical interpretation.
• Reporting and uncertainty - recommended reporting formats, caution about uncertainties in ratio calculations and interpretation limits.
• Free gases for gas relays - guidance on interpreting free gas measurements in protection and relay devices.

Applications

IEC 60599:2015 is practical for:

• Utility and generation asset managers performing transformer condition monitoring
• Maintenance engineers and test laboratories conducting DGA and oil testing
• OEMs and service providers diagnosing faults in oil‑filled equipment
• Asset health programs integrating DGA into predictive maintenance and outage planning

Practical uses include:

• Interpreting lab DGA reports to prioritize inspections or repairs
• Establishing alarm and action levels for in‑service monitoring
• Using Duval triangles and ratio charts to distinguish thermal from electrical faults
• Documenting DGA findings consistently for lifecycle records and risk assessments

Related guidance

• Annex A: equipment application notes (transformers, reactors, bushings, cables, switching equipment)
• Annex B: graphical representations of gas ratios (including new Figure B.4 for on‑load tap changers)
• Bibliography: references to supporting literature and other IEC publications relevant to oil testing and transformer maintenance (see the standard’s bibliography for details)

IEC 60599:2015 is a core reference for anyone involved with oil‑filled electrical equipment condition assessment and DGA interpretation.