ASTM D2300 Test Method for Gassing of Electrical Insulating Liquids
ASTM D2300 Standard Test Method for Gassing of Electrical Insulating Liquids Under Electrical Stress and Ionization (Modified Pirelli Method)
8. Procedure
8.1 Introduce 5 more or less 0.1 mL of the insulating liquid sample into the glass cell by means of a hypodermic syringe.
8.2 Lightly coat the TFE-fluorocarbon plug of the electrode with the test insulating liquid or low vapor pressure silicone grease and insert the electrode into the glass cell.
NOTE 2 - It has been found helpful to place a few drops of the test insulating liquid on top of the TFE-fluorocarbon plug to act as a gas-seal. If there is a leak, use of the oil may help detect it through the appearance of gas bubbles at the top of the Teflon plug.
8.3 Bring the oil bath up to 80°C (for some applications it may be desirable to use 60°C; in either case, report test temperature as indicated in 10.1.1). Suspend the gassing cell and buret assembly in the oil bath at the level indicated in Fig.1, and connect the lead from the outside electrode to ground.
8.4 Attach the gas inlet and outlet connections. When using hydrogen, the gas outlet should lead outside the building, either directly or through a fume hood.
8.5 Close the stopcock (D) and open the valve (E) to allow the saturating gas to bubble through the test insulating liquid and the buret liquid at a steady rate (about 3 bubbles/s) for 10 min.
8.6 Open the stopcock (D) and continue bubbling the
saturating gas through the test insulating liquid for an additional 5 min.
8.7 After a total of 15 min of gas bubbling, close the first valve (E) and then the stopcock (D), making certain the liquid levels in the two legs of the buret are equal.
8.8 Connect the high-voltage lead to the center electrode.
8.9 Place the transparent safety shield in position and take the buret reading after checking the bath temperature.
NOTE 3 - To facilitate reading the buret, it has been found helpful to illuminate the buret scale and to use a magnifying glass or a small optical magnifying device.
8.10 Turn on the high voltage and adjust to 10 kV. Record the time and voltage, as well as the buret level, and check the observation slit on the outer electrode for onset of the gassing reaction.
8.11 After 10 min, record the buret level, voltage, and bath temperature.
8.12 After an additional 50 min, again record the buret level, voltage, and bath temperature, and turn off the voltage.
8.13 To ensure the equipment is operating correctly it is recommended that the buret level be read every 10 min until the test is terminated. A plot of the readings versus time should give a reasonably straight line. If the data are widely scattered, the equipment should be checked and the test rerun.
8.14 For oils with very low gassing tendencies, it may be necessary to stop the test to vent the manometer. The total gas absorbed is the sum of the gas absorbed before and after venting.
8.15 Repeat the procedure on a fresh test specimen, 8.1-8.13.
9. Calculation
9.1 Calculate the gassing tendency as follows:
G = (B60 - B10)K/T
where:
G = gassing tendency, µL/min,
B60 = buret reading, mm, at 60 min of test,
B10 = buret reading, mm, at 10 min of test,
K = buret constant = µL/mm buret reading, (see Appendix X2) and
T = test time of computed gassing rate, min = 60 - 10 = 50 min.
NOTE 4 - This will result in an answer which will be positive (+) if gas is evolved, and negative (-) if gas is absorbed.
9.2 Take the average of the two values of G. If the average values are different by more than 0.3 + 0.26 |X|, then the test should be repeated. Where |X| is the absolute value of duplicate determinations in microliters per minute. Duplicate analyses are performed because it is difficult to detect when a problem occurs during a test. The equation to determine when duplicate analysis are acceptable is based on general experiences and is not derived from a round-robin program for this test method.
9.3 See Appendix X1 to determine the electrical stress for the electrode system and dielectric liquids.
