How Dissolved Gas Analysis Prevents Transformer Fires in Power Grids
When a power transformer fails catastrophically, the result can be fire, explosion, and weeks of disruption. The good news? Most of these failures send warning signals long before they turn destructive. Dissolved gas analysis (DGA) is how you read those signals.
Inside every oil-filled transformer, electrical and thermal stress slowly breaks down the insulating oil and paper.
That breakdown produces specific gases, and those gases tell a clear story about what's happening inside the tank.
By tracking them, you can spot a developing fault while it's still a quiet problem rather than a smoking one.
What Causes a Transformer to Catch Fire or Explode?
Transformers run on insulating oil, a hydrocarbon that cools the windings and core while preventing electrical discharges. Under normal conditions, that oil does its job quietly. Under stress, it starts to break down.
Heat, electrical faults, and arcing all decompose the oil and the solid paper insulation inside the tank. As these materials degrade, they release combustible gases. A high-energy arcing fault can push localised temperatures above 700°C, generating large volumes of gas in a very short time.
That combination of intense heat and combustible gas is what makes a transformer dangerous. If an internal arc continues unchecked, pressure builds rapidly inside the tank. The result can be a violent rupture or an outright explosion, followed by fire. The faults that lead here are often invisible from the outside until it's too late.
How Does Dissolved Gas Analysis Detect a Developing Fault?
Dissolved gas analysis works on a simple principle: different faults produce different gases. By measuring which gases appear in the oil, and in what quantities, engineers can identify both the type of fault and its severity.
Think of the oil as the transformer's bloodstream. As it circulates, it touches every active component inside the tank, carrying chemical evidence of any developing problem. Analysing that oil gives a direct view of the transformer's internal health, with no invasive inspection required.
Each fault leaves a distinct signature:
- Partial discharge (corona): generates hydrogen (H₂) and some methane
- Low-temperature overheating: produces methane (CH₄) and ethane (C₂H₆)
- High-temperature overheating: generates ethylene (C₂H₄)
- Arcing: produces significant amounts of acetylene (C₂H₂) and hydrogen
- Cellulose (paper) degradation: creates carbon monoxide (CO) and carbon dioxide (CO₂)
By tracking these gases, engineers can spot trouble at its earliest stage and prioritise action accordingly.
Stop Transformer Failures Before They Start
Catch acetylene, hydrogen, and moisture as faults develop. With InsuLogix G2, you act on early warnings before they become costly outages.
Why Are Hydrogen and Acetylene the Most Important Gases?
While dissolved gas analysis can measure many gases, two carry the most weight when it comes to fire prevention: hydrogen and acetylene.
Hydrogen is the early warning. It's the first gas generated in most developing faults, appearing during low-energy events such as partial discharge and early thermal stress from around 150°C. Because hydrogen shows up in almost every fault type, it acts as a sensitive signal that something has started to go wrong.
Acetylene is the red flag. It forms exclusively during high-energy electrical faults, particularly arcing, where temperatures exceed 700°C. These are precisely the conditions that break carbon-carbon bonds and, left unchecked, lead to tank rupture and fire. Acetylene almost never appears during normal operation or minor faults, which makes it a near-definitive marker of a serious, active problem.
This specificity is what makes acetylene so valuable. In common operational practice, thresholds of around 1 part per million (ppm) for large, critical transformers and 5 ppm for smaller units justify action, ranging from investigation to urgent measures such as de-energising the unit.
A fault detector that focuses on both hydrogen and acetylene covers the full range, from the first hint of trouble to the high-energy arcing that causes fires.
Why Is Continuous Monitoring Better Than Periodic Oil Sampling?
For decades, the standard approach to dissolved gas analysis meant taking a manual oil sample approximately once a year and sending it to a laboratory. Laboratory analysis remains highly precise and valuable, but it leaves a significant gap.
A single annual sample shows the transformer's condition only at the moment the oil was drawn. It can't reveal how fast gases are building up, and it can't catch a fault that develops between sampling intervals. Some of the most dangerous faults escalate in a matter of weeks, far faster than an annual schedule can detect.
Continuous online monitoring closes that gap. By measuring key gases around the clock in addition to laboratory testing, it detects fault conditions at their earliest stages and reveals the rate of change over time. This distinction matters enormously.
A hydrogen level of 200 ppm means very different things depending on whether it built up over five years or in 48 hours. Only continuous data shows the difference.
The benefits of continuous monitoring are clear:
- Earliest possible warning of developing faults, enabling intervention before damage occurs
- Real-time, remote data that lets engineers respond immediately to alarms
- Trend analysis that reveals fault severity through the rate of gas generation
- Improved safety, with less need for manual sampling in high voltage environments
A flat hydrogen trend might call for routine observation. A sharp spike in acetylene demands immediate action. Continuous monitoring tells you which is which.
How Does the InsuLogix G2 Help Prevent Transformer Fires?
Megger's InsuLogix G2 is an online dissolved gas analysis fault detector built specifically around the gases that matter most for fire prevention: hydrogen, acetylene, and moisture.
For acetylene and moisture measurement, the InsuLogix G2 uses Tunable Diode Laser Spectroscopy (TDLS). A precisely tuned solid-state laser passes through the extracted gas sample and interacts only with acetylene and moisture molecules.
This eliminates the cross-interference from other gases that affects less advanced sensors, producing stable, reliable readings even at very low concentrations.
That sensitivity is critical. The InsuLogix G2 detects acetylene down to 0.5 ppm, giving operators the earliest possible notification of an arcing fault. Since any acetylene signals a high-energy event, catching it at this level provides maximum time to act before a fault turns catastrophic.
The fault detector also delivers data through standard industrial protocols, including Modbus RTU/TCP, DNP3, and IEC 61850, so it integrates directly into SCADA systems and asset management platforms. Twelve configurable solid-state relays trigger immediate alarms the moment a gas concentration or rate of change crosses a defined threshold.
One point deserves emphasis. A fault detector only prevents fires if its alarms are seen and acted upon. The most advanced detection in the world means nothing if warnings go unnoticed. Integrating alarms into your SCADA system, or maintaining a strict schedule of manual data checks, turns detection into prevention.
Turning Early Detection into Lasting Protection
Transformer fires and explosions are among the most damaging events a power network can face, yet they're often preventable. The gases that precede them, especially hydrogen and acetylene, appear well before any visible sign of danger. Dissolved gas analysis reads those gases, and continuous monitoring reads them in time to matter.
The strongest strategy combines continuous online monitoring of hydrogen and acetylene with routine laboratory oil testing for detailed diagnostics. Together, they give operators both the immediate warning and the deeper analysis needed to protect critical assets.
To put this protection in place, start by identifying your most critical transformers, deploy a fault detector like the InsuLogix G2, and build a clear workflow for responding to alarms.
To learn more about how the InsuLogix G2 can strengthen your fire-prevention strategy, schedule a call with one of our experts or download the data sheet.
