Case Study: 28 Hours That Prevented a Catastrophic Transformer Failure

When Every Hour Counts: How Real-Time Monitoring Detected a Manufacturing Defect Before Disaster Struck

After operating flawlessly for two years, a transmission transformer at a major US utility suddenly began exhibiting signs of catastrophic failure. This case study documents how online dissolved gas analysis detected an escalating thermal fault in its earliest stages—providing the narrow window needed to prevent a complete asset loss worth millions of dollars.

What Happened:

At 8:00 PM on December 18, 2018, after months of stable operation, dissolved gas concentrations began rising dramatically. Within 24 hours, the Serveron TM8 monitor alarmed for dangerous acetylene levels, indicating high-temperature metal overheating exceeding 700°C. The monitor automatically accelerated its sampling rate from 6 to 24 times daily, capturing minute-by-minute progression of the developing fault.

The Critical Timeline:

Multiple diagnostic methods—Duval Pentagon, Duval Triangle, IEC Rodgers Ratios—all converged on the same alarming conclusion: a T3 thermal fault generating hot metal gases at an accelerating rate. Just 28 hours after the first gas elevation was detected, the transformer was safely taken offline at midnight on December 20th.

The Root Cause Discovery:

Inspection revealed a loose nut on the PA core leg phase 1, causing localized overheating. Factory analysis uncovered the underlying issue: manufacturing thread damage that prevented proper torque application during assembly. Years of operational vibration had gradually loosened the compromised connection until thermal runaway began.

The Bottom Line:

Without continuous monitoring, this fault would have progressed undetected through a weekend, almost certainly resulting in catastrophic failure, prolonged outage, and potential collateral damage. This case study provides forensic-level detail on gas progression patterns, diagnostic interpretation, and the physical evidence that validates online monitoring as essential insurance for critical assets.

Download to see the actual DGA trends, inspection photos, and hour-by-hour timeline of this near-miss event.