ASTM D831 Standard Test Method for Gas Content of Cable and Capacitor Oils
10. Precision and Bias
10.1 Precision - This test method has been found to be reproducible to more or less 0.02 % gas content for gas contents on the order of 0.10 % (Note 6); for samples of higher gas content the absolute error will be somewhat greater but the percentage error somewhat less.
NOTE 6 - Consider the case of an oil with 0.10 % gas. For normal procedure, values of initial pressure and end point would be 0.100 and 0.300 mm Hg, respectively. This pressure increase would be developed by 50 mL of oil tested at 50°C in an apparatus having a total fixed-space volume of approximately 225 mL, the components of which have the following volumes and temperatures: degassing chamber, 125 mL and 50°C; cold trap, 25 mL and -195°C; pressure gage, 75 mL and 27°C. The Stokes gage (Model 276-AA) can be read to more or less 0.005 mm below 0.100 mm; more or less 0.025 mm between 0.100 and 0.700 mm; and more or less 0.050 mm between 0.700 and 5.000 mm. Oil volume can be read to more or less 0.05 mL. Assuming errors in pressure and volume readings adding to give maximum deviation, the resultant error would be more or less 0.02 % gas content.
10.2 Bias:
10.2.1 A statement on the bias of this test method cannot be made because there is no material available having an accepted reference value.
10.2.2 The expected value of the gas content determined by this test method is essentially the true gas content provided that there are no leaks in the apparatus, there is no water vapor present, and an adequate water trap is used in series with the vacuum gage, and provided that the techniques for achieving maximum evolution of gas from the sample are carefully followed.
11. Keywords
11.1 cable oil; capacitor oil; electrical insulating oil; gas content; oil-filled cable
