Ecol tests: Resistivity/Dielectric Loss Coefficient

method description:

The measurement of resistivity and dielectric loss factor of oil is carried out in a special vessel – a measuring capacitor.
Resistivity (specific electrical resistance) is the quotient of the intensity of a constant electric field and a fixed value of the current density. The dielectric loss coefficient tgd is a measure of the energy loss in the dielectric and is defined as the ratio of the current associated with the losses in the dielectric to the current associated with the charge build-up on the facings of the capacitor. The energy losses during dielectric polarisation depend on the leakage current, the rotation of the dipoles in dipole polarisation and the charge displacement.

interpretation of results:

Both the resistivity and dielectric loss of oil are dependent on the content of polar molecules – dipoles, capable of carrying electric charges or able to interact with an alternating electric field. The presence of these compounds in oil is related to the chemical structure of its molecules and the presence of impurities and products of oil degradation and oxidation.

The resistivity and dielectric loss values of a given oil sample depend on the measurement temperature. The recommended measuring temperature is 90° C (less frequently 50°, 20° or 100° C). Only measurements made at the same temperature can be compared.