| Property | Transformer Oil | Cable Oil | Capacitor Oil | Askarels | Silicone Oils |
|---|---|---|---|---|---|
| Breakdown strength (20 C, 2.5mm sphere gap) | 150 | 300 | 200 | 200-250 | 300-400 |
| Relative Permittivity (50Hz) | 2.2-2.3 | 2.3-2.6 | 2.1 | 4.8 | 2-73 |
| Loss Tangent (50Hz) | .001 | .002 | 0.25E-3 | 0.60E-3 | .001 |
| Loss Tangent (1 kHz) | .0005 | .0001 | 0.10E-3 | 0.50E-3 | 0.1E-3 |
| Resistivity (Ohm -cm) | 1e12-1e13 | 1e12-1e13 | 1e13-1e14 | 2e12 | 3e14 |
| Specific Gravity at 20 C | 0.89 | 0.93 | 0.88-0.89 | 1.4 | 1.0-1.1 |
| Viscosity at 20 C (cStokes) | 30 | 30 | 30 | 100-150 | 10-1000 |
| Refractive Index | 1.4820 | 1.4700 | 1.4740 | 1.6000 | 1.5000-1.6000 |
| Saponification | 0.01 | 0.01 | 0.01 | <0.01 | <0.01 |
| Thermal Expansion | 7e-4/deg | 7e-4 | 7e-4 | 7e-4 | 5e-4 |
| Max permissible Water content (ppm) | 50 | 50 | 50 | <30 negligble | <30 negligible |
Pure liquids often have much higher breakdown strengths than commercial liquids. For instance, the addition of 0.01% water to insulating oil reduces its breakdown strength to 20% of the "dry" value. Compare, for example, the breakdown for Transformer Oil is usually taken as 150 kV/cm (see above table), but when highly purified, it is almost 8 times that, or 1000 kV/cm.
| Liquid | Max Breakdown Strength MV/cm |
|---|---|
| Hexane | 1.1-1.3 |
| Benzene | 1.1 |
| Transformer Oil | 1.0 |
| Silicone | 1.0-1.2 |
| Liquid Oxygen | 2.4 |
| Liquid Nitrogen | 1.6-1.9 |
| Liquid Hydrogen | 1.0 |
| Liquid Helium | 0.7 |
| Liquid Argon | 1.10-1.42 |
Copyright 1998, Jim Lux / filename here / revised date / Back to HV Home / Mail to Jim