CIGRE Technical Brochures on DGA: A Reference Guide for Asset Managers

For transformer asset managers working at the leading edge of DGA practice, CIGRE Technical Brochures published by Study Committee A2, the international technical body responsible for power transformers, represent some of the most technically detailed and internationally validated guidance available. These brochures address DGA topics that fall outside or beyond the scope of the primary regional standards, IEEE C57.104-2019 [1] and IEC 60599:2022 [2], and are referenced by those standards' working groups as supplementary material.

Understanding which CIGRE publications are most relevant to DGA practice, and what each one contributes, helps asset managers identify where additional guidance applies to their specific situation.

How CIGRE Technical Brochures Are Produced

CIGRE working groups bring together engineers and researchers from multiple countries, utilities, manufacturers, and research institutions. Each working group is convened to address a specific technical question; members contribute data, analysis, and expertise over a multi-year development period. The resulting brochure is peer-reviewed by the international technical community before publication.

This process produces documents that reflect broad international experience and represent genuine technical consensus, not a single organisation's perspective. For topics where national standards reflect a particular geographic operating environment (the IEEE standards are calibrated primarily against North American utility experience; IEC standards against European), CIGRE brochures provide the synthesis across operating environments that neither regional standard alone provides.

Jim Dukarm's participation in CIGRE Study Committee A2 working group activities over many years ensures that R-DGA methodology reflects and contributes to this international technical consensus.

The Key DGA-Relevant CIGRE Technical Brochures

TB 771: Improved DGA Diagnosis Criteria and Non-Mineral Oils [3]

CIGRE TB 771, produced by Working Group A2.43, is the most important recent CIGRE publication for DGA practitioners. It addresses two closely related topics:

Improved DGA diagnosis criteria for mineral oil. Working Group A2.43 reviewed the existing DGA interpretation frameworks, including IEEE and IEC standards, Duval Triangle and Pentagon, and Rogers and IEC ratios, and proposed updated and improved diagnostic criteria based on a more extensive and internationally diverse dataset than the criteria underlying the regional standards. These improved criteria form the basis for updates in the 2022 IEC 60599 revision and inform ongoing IEEE C57.104 working group deliberations.

DGA interpretation for non-mineral insulating fluids. TB 771 is the primary international reference for DGA interpretation in transformers filled with natural ester fluids, synthetic ester fluids, and load tap changers. Natural ester fluids produce different dissolved gas profiles from mineral oil at the same fault temperatures, generally higher CO and CO₂ generation and different hydrocarbon ratios, and the mineral oil threshold values in C57.104 [1] and IEC 60599 [2] do not apply. TB 771 provides fluid-specific guidance for each non-mineral oil type. For utilities deploying ester-filled transformers, TB 771 is not optional reading. It is the document that makes their DGA programme valid.

TB 812: Transformer Reliability Survey [4]

TB 812, produced by Working Group A2.49, presents the results of CIGRE's most recent comprehensive international transformer failure survey. It is the definitive reference for transformer failure statistics, covering:

• Failure rates by transformer type, voltage class, and service age
• Failure mode distribution: insulation failures, tap changer failures, bushing failures, terminal failures, core failures
• Age-related failure probability curves
• The relationship between observed DGA anomalies and subsequent failure in monitored populations

The empirical failure data in TB 812 is foundational to the reliability-engineering framework used by R-DGA methodology. The Hazard Factor metric's calibration, mapping CSEV values onto failure probability, is derived from the statistical relationship between condition severity indicators and failure events in the kind of large, diverse transformer population that CIGRE's survey represents.

TB 812 is also the reference for understanding which failure modes are detectable by DGA (dielectric insulation failures, thermal overheating faults) and which require other monitoring methods (mechanical deformation, external bushing failures).

TB 630: Online Monitoring of Transformers [5]

TB 630, produced by Working Group A2.44, provides the technical framework for online DGA monitoring deployment. It covers:

• Technical performance characteristics of different online monitoring technologies (photoacoustic, infrared, electrochemical, gas chromatography)
• Signal conditioning and data quality requirements for continuous sensor data
• Selection criteria for which transformers justify online monitoring investment
• Integration of online monitoring data with periodic laboratory sampling
• Alert logic approaches and their relative merits

TB 630 is the document that establishes the technical case for why rate-of-change alerting provides more value than fixed threshold alerts on raw online sensor data, the same principle underlying Monitor Watch's analytical approach. CIGRE's conclusion that signal conditioning before R-DGA calculation is necessary for reliable online monitoring results is directly reflected in Monitor Watch's design.

TB 445: Guide for Transformer Maintenance [6]

TB 445, produced by Working Group A2.34, is the comprehensive CIGRE reference for transformer maintenance strategy. It provides the framework for:

• Condition-based maintenance versus time-based maintenance
• Integration of multiple condition indicators (DGA, oil quality, electrical tests, thermography) into maintenance decisions
• Life management for ageing transformer fleets
• The relationship between maintenance investment and failure risk reduction

TB 445's framework for integrating DGA into a broader multi-method condition assessment programme provides the context for understanding DGA's role: the continuous monitoring layer that provides the most timely risk signal, to be supplemented by targeted electrical testing when DGA identifies units warranting closer examination.

TB 443: DGA in Non-Mineral Oils and Load Tap Changers [7]

TB 443, produced by Working Group D1.32, was the precursor to the ester fluid guidance later expanded in TB 771 [3]. It covers DGA interpretation for:

• Silicone oil-filled transformers
• Load tap changers (which may use oil different from the main tank)
• Early guidance on natural ester and synthetic ester fluids

For utilities with legacy ester or silicone oil-filled transformers, TB 443 remains relevant alongside the more recent TB 771.

TB 296: Recent Developments in DGA Interpretation [8]

TB 296, produced by Working Group D1.01/A2.11, provided an international perspective on DGA interpretation method developments and was influential in the development of the Duval Triangle and Pentagon methods and the IEC 60599 ratio method updates. Though older (2006), it remains a useful reference for understanding the technical reasoning behind the major fault classification methods that are now incorporated into the regional standards.

Accessing CIGRE Technical Brochures

CIGRE Technical Brochures are available through the CIGRE e-library. Corporate CIGRE membership provides access for engineering staff within member organisations; individual membership is available for practitioners wanting access to the full publication library. Many university libraries in countries with CIGRE national committees also provide access.

For the scientific foundations of R-DGA methodology and its relationship to CIGRE guidance, visit the Science page. For educational resources on DGA interpretation, visit the Learn page. To discuss how CIGRE guidance applies to your DGA programme, contact us.