Video: Transformer monitoring: what 42 technical webinars teach

Video transcript

42 technical webinars on transformers, summarised. Temperature, gas, moisture, bushings, tap changers and through faults: what each one tells you, and what it costs to ignore. The sessions open with a question that frames everything else. What is the most important part of a transformer? The answer is that there is no single one: it is a collection of sub-systems, and a failure in any of them can take the unit off line.

The measurement that governs the life of the unit is the winding hot spot, and it cannot be measured with a probe in the oil. It is calculated, and the sessions are clear about how wrong the old gauges can be. And the cost of getting it wrong is not linear. Under the IEC loading guide, every 6 degrees above 98 doubles the rate at which the paper ages. Gas is the second pillar, and the sessions teach it as a thermometer. Each fault temperature produces its own gas,

so the gas that appears tells you how hot the fault is. Hydrogen gets its own treatment, because its physics are awkward. It is the least soluble of the diagnostic gases, so it leaves the oil and collects in the headspace at roughly 20 to one. Moisture is the one the sessions return to most often, and the reason is a number that surprises people. In a 50 MVA transformer with one and a half percent water in the paper, almost all of the water is in the paper, not the oil.

And how much appears in the oil depends entirely on temperature. And knowing the water in the paper is not academic. Three practical limits depend on it. Bushings take 6 of the 42 sessions, and the reason is the severity. A bushing failure is sudden, and about half the time it starts a fire that destroys the transformer with it. The sessions then explain why the online measurement works, and it is the construction of the bushing itself.

And what the monitor looks for is balance. Three healthy bushings produce 3 currents that cancel. When one changes, the sum stops being zero. The sessions add a warning: at 10 kilovolts an offline test may miss contamination that shows plainly at rated voltage. The tap changer is the only part of a transformer that routinely moves, and the failure statistics from one large utility make the point. Flashover in the tap changer was the single largest category,

and 14 of those 28 cases went on to destroy a winding. Four measurements watch it, and the cleverest is the motor energy. Most mechanical problems in the drive change the power the motor draws, so the joules used per tap change become a picture of the linkage, the gears and the lubrication. Two more stresses come from outside the transformer and are worth monitoring precisely because they accumulate. Through faults, and the harmonics from a saturated core.

Across 42 sessions, 5 things are repeated more than anything else. Transformer monitoring, from Amperis.