2023 in Review: Trends in Transformer Diagnostics and R-DGA Methodology

2023 was a year in which several long-running trends in transformer asset management became impossible to ignore. Ageing infrastructure, rising capital replacement costs, the escalating impact of the energy transition on transformer loading profiles, and growing interest in quantitative fleet risk assessment all intensified. Together they reinforced why rigorous DGA methodology matters more now than at any previous point in the industry's history.

The Infrastructure Ageing Reality

The North American transmission transformer fleet continues to age. CIGRE TB 812 [1], the most comprehensive international analysis of transformer failure statistics, documents that failure probability increases substantially as transformers age beyond their original design lives. A large fraction of the transmission fleet was installed in the 1960s through 1980s; these units are now 40–60 years in service, well past the 30–40 year design life assessments that were standard when they were built.

The consequence of this ageing profile is amplified by replacement supply constraints. Custom-specification large power transformers now carry manufacturing and delivery lead times of 18–24 months. For utilities managing ageing transmission assets, this means that a transformer failure without warning creates an outage that cannot be resolved quickly. The economics of proactive condition monitoring, including rigorous DGA with population-based severity assessment, are straightforward against this backdrop: early detection of developing faults enables planned intervention within available outage windows rather than emergency response after failure.

This dynamic drove sustained demand throughout 2023 for DGA analytical approaches that go beyond threshold comparison: specifically, for methods that produce fleet-level risk rankings based on population-normalised cumulative severity and failure probability [2].

Growing Adoption of R-DGA Methodology

Reliability-based DGA saw continued adoption growth in 2023, particularly among utilities seeking to move from reactive DGA review to systematic fleet management. The core value proposition, that CSEV and HF provide a ranked, defensible view of fleet risk that threshold methods cannot produce [2], resonated with asset management teams whose engineers are managing larger fleets with smaller internal resources.

Two specific contexts drove adoption conversations:

Fleet prioritisation for capital planning. Utilities entering multi-year capital investment programmes need defensible prioritisation criteria for transformer replacement decisions. A ranked fleet list by HF, backed by published R-DGA methodology [2] and validated population data, provides a regulatory-quality evidence base for capital allocation decisions that a list of C57.104 [3] condition exceedances does not.

False alarm reduction. Multiple utilities reported reducing the volume of elevated DGA results requiring follow-up investigation after adopting R-DGA fleet screening, not because fewer transformers were generating gases, but because R-DGA's population context revealed that many of the threshold exceedances corresponded to transformers operating within normal parameters for their age and service history. Directing inspection resources toward the true high-risk units rather than the threshold-triggered list produced better outcomes with the same resource base.

Online Monitoring Reached a Deployment Inflection

2023 appeared to be a year in which online DGA monitoring crossed from experimental to standard practice for a meaningful subset of critical assets. Utilities that began online monitoring deployments as single-unit pilots in 2019–2021 expanded to systematic deployment on classes of critical units, including specific voltage classes, specific substation configurations, or units identified through fleet screening as combining high consequence and elevated CSEV/HF.

The key challenge that emerged in broader deployment was data management: how to maintain a coherent fleet risk picture when DGA records for individual transformers mix periodic laboratory samples and continuous online sensor data. Monitor Watch's integration of both data types under a single R-DGA analytical framework addressed this challenge directly, and the data management question drove significant interest in the platform through the year.

Energy Transition and Transformer Stress

The energy transition continued to impose new stresses on transformer fleets that were not part of the original design envelope. Two specific mechanisms were prominent in technical discussions throughout 2023:

Distributed solar and reverse power flow. The growth of rooftop and utility-scale solar is creating bidirectional power flows through distribution transformers that were designed for unidirectional operation. Loading profiles that deviate significantly from original design assumptions accelerate transformer ageing through thermal cycling mechanisms documented by McNutt and others, and produce gas generation patterns that can differ from those generated by conventional loading.

EV charging load concentration. As electric vehicle adoption expands, distribution transformers serving residential neighbourhoods with high EV penetration are experiencing load peaks significantly above what their thermal models were designed for. The chemical signature of this accelerated thermal stress, CO and CO₂ accumulation alongside elevated ethylene, is detectable by DGA and trackable through CSEV trajectory analysis.

Both mechanisms reinforce the need for DGA programmes sensitive to trajectory and rate-of-change rather than static threshold comparison [2].

Standards Activity: Alternative Fluids and DGA

2023 saw continued international standards activity on DGA interpretation for transformers filled with alternative insulating fluids, including natural esters, synthetic esters, and silicone oils. CIGRE TB 771 [4], produced by Working Group A2.43, remains the primary international reference for DGA interpretation guidance beyond mineral oil. As utilities deploy ester-filled transformers at an increasing rate for fire risk reduction and environmental performance, the demand for validated interpretation criteria specific to those fluids intensified.

The problem is not trivial: gas generation characteristics differ substantially between mineral oil and natural ester fluids. Applying the threshold values in IEEE C57.104 [3] or IEC 60599 [5] directly to ester transformer DGA results produces systematically incorrect classifications. Utilities building ester transformer fleets without fluid-appropriate DGA interpretation are flying partially blind.

Jim Dukarm's ongoing participation in CIGRE Study Committee A2 activities keeps R-DGA methodology current with the evolving international consensus on alternative fluid interpretation, and ensures that TOA's analytical framework accommodates fluid type as an interpretive parameter.

Looking Ahead to 2024

The themes that defined 2023 are not resolving. They are intensifying. Fleet ageing continues, the energy transition accelerates, and the case for quantitative, population-based DGA methodology grows stronger as the cost of inadequate condition assessment becomes more visible in maintenance budgets and grid reliability incidents.

For technical resources on R-DGA methodology, visit the Science page and the Learn page. To discuss how TOA and Monitor Watch might improve your organisation's DGA programme, contact us.