9 Expression of results
Results may be calculated using the following equation:
where
G is the conductance, in siemens (S);
C is the capacitance, in farad (F);
ω is the angular frequency, in radian/second (rad/s), ω = 2πf;
f is the chosen frequency, in Hertz (Hz).
NOTE Provided that the relative permittivity εr at the measuring temperature is known the conductivity of the liquid can be calculated by the following equation:
where ε = ε0εr
10 Test report
The report shall include the following:
- sample identification;
- temperature of test;
- measured values of G and C;
- calculated values of tan δ.
11 Precision
11.1 General
The precision of a test method is the closeness of several experimental results obtained on identical samples. Assessment of the precision is given by the repeatability r and reproducibility R, both defined in ISO 5725-1. Calculation methods are given in ISO 5725-2, ISO 5725-3 and ISO 5725-4.
The values of r and R for the dielectric dissipation factor of an insulating liquid depend on the nature of the liquid under test, whether it is unused or used, and that of the temperature; these values are impaired when tan δ is very low (less than 10(-4)), as found in highly insulating liquids which are readily affected by impurities, handling, cleaning of the test cell, etc.
11.2 Repeatability (r)
If two measurements A and B are obtained in one laboratory at room temperature, they can be considered acceptable if the absolute difference |A - B| satisfies the following relation:
|A - B| < αMin (A,B)
where Min (A,B) is the lowest of the two values A and B.
For unused insulating liquids: α = 0,2
For used insulating liquids: α = 0,1
11.3 Reproducibility (R)
If two measurements A and B are obtained in two different laboratories at room temperature, the above relation is still valid with the following values for α:
For unused insulating liquids: α = 0,35
For used insulating liquids: α = 0,20
11.4 Examples of r and R
Examples of r and R values are given in the table below and are deduced from inter-laboratory tests carried out at room temperature on mineral insulating oils.