What Are You Looking For?
Oil-immersed transformers, vital for power distribution and energy conversion, operate efficiently when thermal equilibrium between internal heat generation and heat dissipation is maintained. However, when temperatures rise abnormally—especially when the oil temperature exceeds the typical range by over 10°C or the load remains constant but internal temperature continues to climb—a malfunction is often at play. These issues may stem from internal component failures or external environmental conditions. Understanding the root causes is essential to prevent irreversible damage and ensure long-term operational safety.
When internal heat production outweighs the transformer's cooling capabilities, the thermal balance collapses. Internal malfunctions can precipitate localized or systemic temperature anomalies, often detectable through diagnostic methods such as gas analysis, resistance measurements, or acoustic monitoring.
Tap changers regulate voltage by adjusting the transformer's turns ratio. If the contact pressure is insufficient or the contact surfaces are contaminated, electrical resistance increases. This heightened resistance results in localized heating at the contact points. Particularly after tap adjustments or during overload conditions, contact degradation accelerates.
Such contact faults can be diagnosed through frequent light gas (buchholz relay) activation, declining oil flashpoints from sample testing, or by measuring the DC resistance of the windings to assess tap contact integrity.
Damage to insulation between adjacent winding turns can create a closed-loop short circuit, forming circulating currents. These parasitic currents generate intense localized heating and reduce the effective number of turns in the coil, impairing electromagnetic performance.
Factors contributing to inter-turn shorts include:
Poor manufacturing practices leading to mechanical damage.
Thermal aging of insulation due to prolonged high temperatures.
Axial displacement from electromagnetic forces abrading insulation surfaces.
Advanced short-circuit faults often manifest as rising oil temperatures, audible bubbling noises from localized boiling, and progressive gas relay activation—from light to heavy gas responses. Oil analysis reveals deteriorated quality, and resistance measurements can confirm coil anomalies.
The transformer's core comprises silicon steel laminations insulated from each other to minimize eddy current losses. When this insulation is compromised—through mechanical stress or thermal aging—eddy currents surge, causing concentrated heating.
Insulation failure in through-bolts exacerbates this effect. Mild cases generate inconspicuous hot spots, while severe cases elevate oil temperatures, trigger gas relay alarms, and reduce the oil’s flashpoint. In extreme situations, these faults transition from light to heavy gas protection stages.
Transformer oil serves multiple roles: insulation, cooling, and arc suppression. A deficiency in oil volume or obstructions within cooling ducts impedes circulation, diminishing heat dissipation efficiency. Consequently, heat accumulates, raising internal temperatures beyond safe thresholds.
Beyond internal faults, environmental and operational factors can severely impact thermal regulation.
Transformers generate heat through core losses (hysteresis and eddy currents) and winding losses (copper losses). While core losses remain relatively constant and structurally inherent, copper losses escalate with load increases.
Under heavy overloading, copper losses dominate thermal production, resulting in rapid temperature rises. Prolonged overloading is a direct path to insulation breakdown and eventual transformer failure.
Ventilation is critical to convective cooling. Transformer rooms with obstructed air intakes or excessive dust accumulation impair airflow, leading to inadequate heat dispersion. While internal heat generation remains constant, impaired dissipation causes temperatures to climb.
Monitoring air temperature 1.5–2 meters from the oil tank, at a height equal to half the oil tank’s height, can serve as an indicator. A differential of 8–10°C above ambient temperature signals insufficient ventilation—prompting urgent airflow optimization.
In addition to passive heat dissipation through cooling fins, transformers often employ enhanced systems: forced-air cooling, oil circulation pumps, or even water cooling for high-capacity units. Malfunctions in these systems—whether mechanical, electrical, or hydraulic—result in insufficient cooling, causing operational temperatures to spike rapidly.
Regular inspection and maintenance of these auxiliary cooling systems are critical to sustaining transformer health, particularly in high-load or high-temperature environments.
Transformer overheating is a multifaceted issue that demands a comprehensive diagnostic approach. Whether the cause lies within tap changer contacts, winding insulation, core integrity, or external cooling deficiencies, swift identification and intervention are imperative. With escalating demands on electrical infrastructure, preventive maintenance and rigorous condition monitoring are no longer optional—they are essential safeguards against catastrophic transformer failure.
