Critical transformer oil properties for power equipment Which pair lists the most important specifications typically emphasized for transformer insulating oil used in high-voltage apparatus?

Introduction / Context:
Transformer oil provides both electrical insulation and heat transfer. Standards and acceptance tests prioritize properties that ensure safe dielectric performance and resistance to ignition under fault or thermal stress. Knowing which specifications are most critical helps in maintenance and procurement of power equipment oils.

Given Data / Assumptions:

• Focus on primary, safety-critical performance metrics.
• Mineral insulating oil used in transformers and switchgear.
• Comparing dielectric strength, flash point, viscosity, and other properties.

Concept / Approach:

Dielectric strength (breakdown voltage) directly measures the oil’s ability to withstand high electric fields without failure—arguably the most important electrical property. Flash point indicates the temperature at which oil vapors ignite; a high flash point is critical for fire safety. While viscosity matters for cooling (affecting convection and pumping), it is usually secondary to the must-meet dielectric and safety thresholds when defining the most important pair of specifications.

Step-by-Step Reasoning:

Verification / Alternative check:

Industry standards (e.g., IEC/IS/ASTM guides) list breakdown voltage and flash point among primary acceptance criteria, with additional checks like water content, acidity, interfacial tension, and dissipation factor also important.

Why Other Options Are Wrong:

• Dielectric strength and viscosity: lacks a direct safety metric.
• Viscosity and flash point: omits the key electrical breakdown property.
• Acid number and pour point: important for aging and low-temperature behavior but not the top two for initial serviceability.

Common Pitfalls:

Overemphasizing viscosity for cooling while neglecting that inadequate dielectric strength or low flash point can cause immediate catastrophic failures.

Final Answer:

Dielectric strength and flash point