EN
Thermometer Examination and Test
Examination of transformer thermometers: oil and winding gauges, set points and alarm-trip circuit tests with portable verification, reported.
Transformer thermometer examination and testing audits the top oil, bottom oil and winding (warminding) thermometers of oil-filled transformers together with their contactor set points: correct reading, clean-sensitive calibration and reliable signal production to the protection circuit are verified. The thermometer is the leading operating indicator watching the transformer's overheating due to overload or internal fault: a drifted setting or a faulty probe may end in fans-pumps not starting and no alarm-trip, silencing a thermal accident that can reach fire.
Examination and Test Items
- Verification reading: Comparative measurement against a fixed reference (calibration block/portable thermometer); pointer-digital reading consistency; deviation assessed against the manufacturer band (typically ±2-3°C or the standard's value).
- Contactor set points: Field or pen testing that adjustable thresholds engage-disengage correctly in the fan-pump-alarm-trip scenarios; hysteresis control (no rapid open-close cycling).
- Probe-well integrity: Dirt-vibration damage in the thermowell, probe cable gland watertightness, PT100/thermocouple measurement circuit continuity; probe insertion depth in the well (conduction error).
- Mounting-cabin access: Dial cleanliness-light conditions, operator set-point adjustment authorisation and labelling; broken protection cover.
- Integration: SCADA-automation signal accuracy, remote reading (analog 4-20 mA or digital comms) calibration; alarm log time stamp control.
Why Important and Frequent Defects
Overheating multiplies the life loss of insulation paper (Arrhenius rule: temperature rise accelerates ageing), ending in a burn-residue-rupture chain. The thermometer is therefore not merely an indicator but the sensor of protection and operation decisions. Frequent defects: set points drifting over years, contactor failure or sticking, probe coated in sludge (slow but permanent error), moisture ingress from loosened glands and broken dial glass. Test results must be taken in coordination with periodic function tests of protection relays and the alarm system; verifying a single device does not guarantee the rest of the chain. During verification, dial reading error and sensor error are separated: if the gauge reads true while the circuit drifts, the fault is on the panel side — this distinction directly cuts maintenance cost.
Legislation and Outcome
The examination is within scope under Law No. 6331, the Regulation on High Current Electrical Installations and the work equipment maintenance duty; instrument verification runs with portable references under TS EN ISO 17025 traceability, and the protection circuit side ties to panel-protection coordination specifications. The verification protocol and deviation table connect to the signed report. Thermometer examinations are part of our Transformer Tests and Analyses group; for integrated programmes combine planning with our Oil Leak Inspection and Buchholz Examination services; book via our contact page.
FAQ on Thermometer Examination and Test
The top-oil thermometer, an immersion type where needed, a winding thermometer on dry types; additionally magnetic-pointer analogue gauges, PT100-class immersion sensors and contacts (maximum-alarm-trip) sending signal to protection-automation. On cooled transformers the oil inlet-outlet and winding hot-spot computed temperature are tracked separately. These elements are the input of both the operating limit and the cooling-control logic.
Gauge readability-broken glass-cover, the soundness-corrosion of the capillary-mechanical joint, verification of the magnetic contact setpoint and the limit-contact function trial (alarm-trip-contactor) are performed. A comparative error measurement (accuracy check) against a reference portable probe (calibrated temperature block-bath) confirms whether the deviation is within limits. PT100-sensor-circuit continuity-insulation and signal verification are also part of the package.
A thermometer reading low hides real overheating; this speeds cellulose ageing and creates oil-degradation and fault risk. One reading high produces unnecessary load-shedding-cooler running and alarm fatigue. In an overload-short-circuit scenario, the delay of the protective trip depends on the accuracy of the temperature reading. That is why verification-calibration results enter the reference baseline.
Visual-contact-alarm checks follow the operating routine (e.g. monthly), while reference-probe verification with calibration is generally in the yearly periodic control package. After a suspect reading, gauge damage, cooling-automation fault or an over-temperature event, verification is repeated. The relevant standards (IEC 60076-2 temperature rise, TS EN 61557 measuring-device approach) and the manufacturer manual are the reference; result-tolerance and change suggestion enter the report.