A Three-Part Blog Series by ZTZ Services
Is Data Enough?
Parts 1 and 2 of this series examined the challenges of integrating inverter-based resources (IBRs) into the existing power grid and the specific technical stresses placed on transformers.
Utilities have been adapting over the last decade through investments in energy storage and active transformer monitoring. These efforts help buffer supply extremes and provide real-time insight into transformer health. In doing so, the very nature of the power grid has evolved, and operating rules continue to be rewritten.
However, a key challenge remains: Standard dissolved gas analysis (DGA) and bushing interpretation methods were developed under conventional loading assumptions that no longer fully match today’s grid conditions. The following three questions illustrate key evolving relationships between current IBR operating conditions and transformer monitoring data. In each case, the necessary monitoring equipment is already installed or readily available. These points show the real gap is not in the technology. It is in the analytical frameworks used to interpret the data.
Three Questions Worth Asking
1. When an IBR trips, does your monitoring data tell you what kind of stress event just occurred, or only that something happened?
Standard DGA tools, including the Duval Triangle, IEC gas ratios, and rate-of-change trending, compare gas concentrations against thresholds developed under traditional loading profiles. They do not distinguish how the gas was generated. An IBR curtailment or trip that shifts load in seconds creates a steeper hotspot rise, a sharper thermal gradient, and a different gas generation profile than a conventional 30-minute ramp.
The ppm/day rate-of-change metric is particularly sensitive to these episodic, high-intensity events. Correlating these spikes with SCADA records of curtailments, frequency response activations, and generation trips allows asset managers to separate normal IBR-driven gas acceleration from developing internal faults. That distinction directly informs maintenance prioritization.
Continuous bushing monitoring adds a second channel. Voltage disturbances appear immediately in bushing power factor or capacitance, while purely thermal events show up later in the DGA record. This timing difference creates a clear diagnostic signature: DGA acceleration alone points to thermal load transfers, while simultaneous movement in both channels indicates a voltage disturbance. This cross-channel approach has not yet been formalized in standards, but the large installed base of monitors at IBR-connected substations offers the perfect dataset to develop it.
2. Are your monitoring baselines built for a load profile your transformer no longer experiences?
Traditional DGA and bushing thresholds assume periodic thermal recovery intervals during which gas generation and dielectric stress relax toward baseline. That assumption no longer holds when IBR variability is superimposed on sustained high base loading from electrification, industrial customers, or data centers.
This creates persistently elevated gas generation rates and bushing parameter drift, not due to faults, but because the transformer never reaches the recovered state assumed in fleet-wide thresholds. Beware the dual risk: overly sensitive thresholds generate false alarms that erode confidence, while desensitized thresholds may mask genuine issues.
A practical solution is typically to segment high-IBR substations in your fleet management system, develop extended site-specific baselines that capture the new elevated steady-state, and set thresholds accordingly.
3. Are you establishing bushing baselines before or after your harmonic environment changes?
The April 2025 Iberian blackout accelerated the industry’s shift toward grid-forming (GFM) inverter technology. EPRI’s comprehensive GFM tutorial (October 2025) and ongoing pilots in the U.S. and China underscore this trend.
Grid-following (GFL) inverters synchronize to the existing waveform; GFM inverters synthesize their own. This produces different harmonic spectra at the point of interconnection. Because bushing power factor is sensitive to the dielectric stress from the terminal voltage waveform, a step change in the harmonic environment can produce an apparent shift in power factor that has nothing to do with bushing degradation.
We’ve seen that without a documented pre-transition baseline and a record of the inverter technology change, operators risk either unnecessary maintenance or missing genuine deterioration. The solution requires no new hardware: log inverter technology by interconnection, treat planned GFM deployments as baseline reset events, and reconcile post-transition data against that record.
Substations without continuous bushing monitoring today have no pre-transition reference. The window to capture that baseline closes when the first GFM unit comes online in the interconnection queue.
Implications for Monitoring Practice
The continued IBR transition is altering the operating environment in which transformer data is generated. Analytical frameworks have not kept pace. Yet before the interpretation gap can be closed, the data itself must exist.
For unmonitored transformers, IBR stresses are accumulating without a record. For monitored units, the question is whether the data is being used effectively. Are ppm/day spikes correlated to dispatch events? Are thresholds site-specific? Have inverter technology changes been documented?
The capability requirement is the same in all cases:
- Continuous online DGA with rate-of-change trending
- Continuous bushing power factor and capacitance monitoring
- Integrated analytics that correlate both channels against operational event logs using site-specific baselines.
Summary: Three Analytical Gaps in IBR-Era Transformer Monitoring
| Issue | Monitoring Data Required | Analytical Gap |
|---|---|---|
| IBR dispatch events produce distinct DGA and bushing stress signatures by event type | Continuous DGA (ppm/day trending); continuous bushing power factor/capacitance; SCADA IBR dispatch logs | Cross-channel correlation methodology linking event type to DGA rate spikes and bushing excursions; no published standard exists |
| IBR cycling without thermal recovery invalidates fleet-wide thresholds | Continuous DGA with extended site-specific baseline; continuous bushing trending | Threshold calibration guidance for no-recovery load profiles; fleet segmentation criteria |
| GFM inverter transition alters harmonic environment, invalidating bushing baselines | Continuous bushing monitoring; pre-transition baseline; inverter technology log | GFM-specific threshold guidance and post-transition reconciliation protocol; no published standard |
Conclusion: From Data to Action
Across this three-part series, we have explored the real-world impacts of renewable integration on existing substation transformers. Part 1 laid out the fundamental shifts in inertia, variability, fault behavior, and supply chain realities. Part 2 detailed the four key stress mechanisms. This final part examined three critical analytical gaps in how DGA and bushing monitoring data are interpreted under IBR-dominated conditions.
At ZTZ Services, we specialize in active transformer monitoring, advanced data analysis, and practical condition-based maintenance strategies tailored to today’s high-IBR environment. Our solutions help utilities move beyond raw data to clear, prioritized actions that protect critical assets, control costs, and support a reliable energy transition.
If you are ready to strengthen your transformer monitoring program and close the analytical gaps discussed in this series, contact ZTZ Services. Our team is here to help you turn monitoring data into extended asset life and greater grid resilience.
References
Analysis in Part 3 draws on EPRI’s comprehensive grid-forming inverter tutorial (October 2025) and publicly reported findings from the April 2025 Iberian blackout.
