Technical Comparison of Properties of Mineral Oil, Natural Ester Oil, Synthetic Ester Oil
- Dec 16, 2025
- 2 min read
Updated: 5 days ago
Mineral oil, natural ester oil, and synthetic ester oil exhibit distinct dielectric properties, thermal stability, environmental impact, and safety making them suitable for different applications in electrical equipment. Mineral oils are sourced from refined crude petroleum, whereas natural ester oils are extracted from vegetable oils (e.g., soybean, rapeseed, and sunflower), and synthetic ester oils are chemically synthesized from alcohols and acids.
Here is a technical comparison of the properties of mineral oil, natural ester oil, and synthetic ester oil:
Particulars | Mineral Oil | Natural Ester Oil | Synthetic Ester Oil |
Breakdown voltage (kV) | Min. 60 | Min. 60 | Min. 70 |
Dielectric dissipation factor (Tan Delta) at 90°C, 50 Hz | Max. 0.010 | ≤ 0.05 | Max. 0.03 |
Water content (ppm) | Max. 10 | Max. 100 | Max. 200 |
Acidity Value (mg KOH/g) | Max. 0.01 | Max. 0.08 | Max. 0.03 |
Total sludge (% mass) | Max. 0.08 | Max. 0.01 | Max. 0.01 |
Density at 90 °C (g/cm3) | Max. 0.89 | Max. 1.0 | Max. 1 |
Viscosity at 40 °C (mm2) | ≤ 12 | Max. 50 | Max. 35 |
Interfacial tension (mN/m) | Min. 40 | 25-30 | 26-30 |
Flash-point (°C) | Min. 135 | Min. 275 | Min. 275 |
Fire-point (°C) | ≥ 160 | Min. 300 | Min. 300 |
Pour-point (°C) | Min. -30 | Min. -10 | Min. -45 |
Mineral oil is a popular and cost-effective choice for insulation due to its suitable breakdown voltage and low dielectric loss. However, it has lower flash and fire points, making it a less preferred option where safety is a priority. On the other hand, natural ester oil is more expensive, but it offers better flash point (≥ 275°C) and fire point (≥ 300°C) values.
Additionally, it has excellent biodegradability and produces low sludge formation that ensures insulation's lifespan and fire safety. However, its lower pour point may limit its use in colder regions. Synthetic ester oil has greater dielectric strength (>70 kV), & thermal and oxidative stability, and excellent low-temperature performance (pour-point Max. -45°C), making it ideal for challenging and harsh circumstances, but at a higher cost.
The selection of an oil depends on specific applications, considering factors such as cost, safety, environmental factors, and performance requirements.