Transformer oil viscosity

Viscosity is a parameter which allows to access performance of many materials. In case of transformer oil, viscosity is connected to its cooling ability.

According to the accepted classification, there are dynamic, kinetic and relative viscosity.

Dynamic viscosity is measured in Pascal=seconds and is determined based on Stokes law or Poiseuille law.

Kinetic viscosity is measured in square meters per second. Its numeric value is obtained by dividing dynamic viscosity of the oil by its density.

Relative viscosity is a parameter obtained from a certain testing method. Its relation with dynamic and kinematic viscosity is described by approximating empirical correlations.

In general, the viscosity of a liquid decreases with the increase of temperature, transformer oil is no exception. Therefore, while measuring this parameter, the exact temperature reading is a must. If special instruments are used for the measurement, these must be equipped with a water bath or other means to maintain the required temperature of the liquid.

There are several types of viscosity meters for the various types of viscosity measurement.