Engineer's Notes: asset condition and diagnostics
The oil tells the story
Faults inside a transformer break down oil and paper into characteristic gases. Regular DGA, interpreted with the Duval triangle and IEC 60599 ratios, finds overheating, partial discharge and arcing long before a trip.
Heat is the clock
Paper insulation ages with temperature. The hot-spot, driven by load and ambient, sets how fast the clock runs. In hot climates, summer peaks can use more life than the rest of the year.
Look and listen
Thermography finds loose and corroded joints; TEV and ultrasonic surveys find partial discharge in switchgear and terminations. Both are quick, non-intrusive and done with the equipment in service.
From data to decisions
A health index combines all the evidence into one score per asset, so maintenance and replacement money goes where the risk is highest.
Frequently asked questions
How do you read a Duval triangle?
Take the three gases methane, ethylene and acetylene, express each as a percentage of their sum, and plot the point on the triangle. The zone it falls in (PD, T1, T2, T3, D1, D2 or DT) indicates the likely fault type. Only use it when gas levels are above normal.
What does acetylene in transformer oil mean?
Acetylene forms at very high temperatures, mostly in electrical arcs and sparking. Even a few ppm in a transformer without an on-load tap changer is a warning sign that needs a quick resample and investigation.
How fast does transformer insulation age?
IEC 60076-7 sets the normal ageing rate at a 98 °C hot-spot for non-upgraded paper. Every 6 K above that doubles the ageing rate, so a few hours of overload on a hot day can use days of normal life.
What do thermography temperature differences mean?
Compare a component with a similar one under the same load. A rise of 1 to 3 K suggests a possible problem, 4 to 15 K a probable deficiency, and over 15 K a major one that should be repaired soon.
What is a transformer health index?
A score, usually 0 to 100, that combines DGA, oil quality, partial discharge, thermography, age, loading and maintenance history. Utilities use it to rank assets and plan maintenance and replacement.
Topics: dissolved gas analysis · Duval triangle · IEC 60599 · IEEE C57.104 · key gases · CO2/CO ratio · hot-spot · relative ageing · loss of life · remaining life · thermography · NETA · partial discharge · TEV · ultrasonic · oil BDV · moisture · health index · condition-based maintenance · RCM
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