Case Study: Managing a Known Problem Asset Until Replacement

Hour-by-Hour Vigilance: How Continuous Monitoring Kept a Failing Transformer Operational Until Scheduled Replacement

Not all transformer stories involve catching unexpected failures. Sometimes the greater challenge is safely managing assets you know are compromised—keeping them operational for critical grid reliability while preventing catastrophic escalation. This case study reveals how granular monitoring enabled exactly that strategy for a 35-year-old transformer with a known gassing history.

The Challenge:

A 336 MVA, 500/230 kV autotransformer installed in 1979 had elevated baseline hydrocarbon gases as high as 100 ppm from historical issues. At 1:00 AM on June 23, 2014, rate-of-change alarms triggered for ethylene and methane, but the transformer was critically needed for grid operations. How do you balance operational necessity against developing fault conditions?

The Strategic Response:

For five days, operators kept the transformer energized under careful surveillance, monitoring gas progression hour by hour. When acetylene climbed to the actionable threshold of 10 ppm, the unit was safely de-energized. Analysis revealed the critical insight: heavy loading directly correlated with accelerating gas production, indicating thermal stress on already-compromised insulation.

The Unique Value:

This case demonstrates online DGA's ability to detect incremental changes even against high baseline contamination—something periodic laboratory testing simply cannot accomplish. Inspection confirmed carbon deposits in damaged core-to-tank insulation. After repairs, the transformer was returned to service with continued slow gassing, scheduled for future replacement.

The Bottom Line:

With hour-by-hour visibility, this compromised asset remained available as operational spare capacity for years rather than being prematurely removed from service or risking uncontrolled failure. The case study quantifies how continuous monitoring transforms risk management for aging fleets, enabling informed decisions about when problem transformers can safely operate and when they must be taken offline.

Download to see the actual gas progression curves, load correlation analysis, and Duval Triangle diagnostics.