Relative Density (Specific Gravity)
Standard Practice for Density, Relative Density (Specific Gravity), or API Gravity of Crude Petroleum and Liquid Petroleum Products by Hydrometer Method, ASTM D1298
Relative density (more commonly, specific gravity) is a direct comparison of the density (mass per volume) of an insulating liquid to water. Water has a specific gravity of 1.000; transformer oil is lighter than water, so the specific gravity is less than one. A typical specification for new oil is 0.84 to 0.91. This is a test of a physical property that relates to the oil’s composition and function. Specific gravity directly affects heat transfer. Specific gravity of oil is affected by the length and structure of the hydrocarbons in the oil. Mixtures of hydrocarbons that perform as transformer dielectric liquids typically have specific gravity within a relatively narrow range.
Specific gravity is a new oil test that is also used for in-service oil. Specific gravity of oil should not change because of aging. Significant changes while in-service are an indication that the oil has been contaminated.
Other dielectric fluids have different ranges for Relative Density (Specific Gravity). The test is used for all types of new and in-service insulating liquids.
Relative density (more commonly, specific gravity) is a direct comparison of the density (mass per volume) of an insulating liquid to water. Water has a specific gravity of 1.000; transformer oil is lighter than water, so the specific gravity is less than one. A typical specification for new oil is 0.84 to 0.91. This is a test of a physical property that relates to the oil’s composition and function. Specific gravity directly affects heat transfer. Specific gravity of oil is affected by the length and structure of the hydrocarbons in the oil. Mixtures of hydrocarbons that perform as transformer dielectric liquids typically have specific gravity within a relatively narrow range.
Specific gravity is a new oil test that is also used for in-service oil. Specific gravity of oil should not change because of aging. Significant changes while in-service are an indication that the oil has been contaminated.
Other dielectric fluids have different ranges for Relative Density (Specific Gravity). The test is used for all types of new and in-service insulating liquids.