In an oil filled transformer, the application of oil is for

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Examoogle · Accepted Answer

both cooling and insulation

Explanation: Transformer oil serves a dual purpose: it acts as a liquid dielectric insulator to prevent electrical breakdown between windings and provides an efficient cooling medium to dissipate heat generated during operation.

Working Principle: The oil is circulated through the core and windings via convection currents or forced pumping to transfer heat to the tank walls or radiators. Dielectrically, it fills the voids in paper insulation, increasing the overall dielectric strength of the transformer system.

Key Formulas: $Q = m \cdot c \cdot \Delta T$ — Basic heat transfer principle governing the cooling efficiency of the oil; $E = V \cdot d^{-1}$ — Dielectric strength relationship where oil improves the breakdown voltage $V$ by increasing insulating property

Key Points: Transformer oil is typically a highly refined mineral oil.; It must have high dielectric strength and low viscosity for efficient heat circulation.; The oil also protects the internal windings from oxidation by preventing contact with air.; Periodic testing (like DGA - Dissolved Gas Analysis) is done to monitor oil health.

Advantages: Provides excellent electrical insulation for high voltage windings.; Efficiently transfers heat from core to the external tank surface.; Extends the life of paper insulation by preventing oxidation.

Disadvantages: Flammability risk (mineral oil).; Requires maintenance to remove moisture and sludge particles.

Applications: Power Transformers; Distribution Transformers; Instrument Transformers (CT/PT)

Additional Info: Transformer oil is typically referred to as Insulating Oil.. Option B is incorrect because, while insulation is a primary function, cooling is equally vital for preventing thermal degradation of the insulation.. The cooling process is enhanced by fins or external radiators attached to the transformer tank.

Answer: C is correct — Transformer oil is essential for both dielectric insulation and thermal dissipation to ensure reliable operation.

Exam Tip: In exams, remember that transformer oil is essentially the 'blood' of a transformer; if the oil fails (due to moisture or sludge), the transformer fails both thermally and electrically.

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