A transformer is a long-lived, silent piece of equipment — if you take care of it. Preventive maintenance is not a luxury: the cost of a full annual inspection program is far less than a single day of outage caused by a fault that could have been detected early.
The Preventive Maintenance Pyramid
Daily/Weekly Round (Transformer In Service)
- Record temperature readings (top oil and windings), load, and voltage.
- Oil level in the conservator tank, and signs of leaks under the transformer and around connections.
- Color of the silica gel and condition of the breather cup.
- Listen for sound: unusual humming or crackling.
- Operation of fans and pumps if present, and cleanliness of the area around the transformer.
Periodic Inspection (Monthly to Semi-Annual)
- Thermal imaging of connections and external bushings under load.
- Oil sample: BDV and moisture, and DGA depending on the transformer's importance.
- Cleaning of radiators and bushings, and testing of alarm circuits.
Annual Tests / Overhaul (Transformer De-energized)
- Insulation resistance with PI.
- TTR and winding resistance.
- Actually test the protection devices: Buchholz, temperature, pressure, level — verify the alarm and trip functions.
- Tap-changer maintenance according to its operation counter and manufacturer's instructions.
The true value of every measurement lies in comparing it with previous ones. A well-documented transformer file (readings, analyses, work done) makes trends speak before faults occur — and it's the first thing any expert called in for a problem will ask for.
Sample answer: Three layers: a daily/weekly round with the transformer in service (temperature, load, oil level, silica gel, leaks, and sound), a periodic inspection every 3-6 months (thermal imaging, BDV and moisture oil sample, and DGA for important transformers), and annual tests with the transformer de-energized (insulation and PI, TTR, winding resistance, an actual test of the protection devices, and tap-changer maintenance). All readings should be documented in a log to track trends.
"Reactive" maintenance: waiting for a fault then repairing it. In transformers specifically, a major fault is often the end of a long, observable deterioration process, and the cost of waiting is the entire transformer plus a service interruption.
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