Suitable transformer oil is defined by a set of electrical, thermal, chemical, and physical specifications. Key parameters include high dielectric breakdown voltage, low moisture content, high electrical resistivity, low dissipation factor (tan delta), and good thermal conductivity. Chemically, the oil must have low acidity, good oxidation stability, and minimal sulfur content to prevent corrosion. Standards such as IEC 60296 and ASTM D3487 specify limits for viscosity, flash point, pour point, and aging behavior to ensure safe long-term transformer operation.
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