ASTM D7150-05

Generation of combustible gases is used to determine the condition of oil-filled electrical apparatus. Many years of empirical evidence has yielded guidelines such as those given in IEEE C57.104, IEC 60599 and IEC 61464. Industry experience has shown that electric and thermal faulted in oil-filled electrical apparatus are the usual sources that generate gases. Experience has shown that some of the gases could form in the oil at low temperatures or as a result of contamination, without any other influences.

Some severely hydro-treated transformer oils subjected to thermal stress and oils that contain certain types of contamination may produce specific gases at lower temperatures than normally expected for their generation and hence, falsely indicate abnormal operation of the electrical apparatus. Some new oils have produced large amounts of gases, especially hydrogen, without the influence of other electrical apparatus materials or electrical stresses. This renders interpretation of the dissolved gas analysis more complicated.

Heating for 164 h has been found to be a sufficient amount of time to reach a stable and characteristic gassing pattern.

This method uses both dry air and dry nitrogen as the sparging gas. This is to reflect either a electrical apparatus preservation system that allows oxygen to contact the oil or one that is sealed from the outside atmosphere. Oils sparged with air generally produce much more hydrogen as a percentage of the total combustible gas content as compared to oils sparged with nitrogen as these produce more hydrocarbons in relation to hydrogen.

1.1 This test method describes the procedures to determine the low temperature (120C) gassing characteristics of insulating liquids specifically and without the influence of other electrical apparatus materials or electrical stresses. This test method was primarily designed for insulating mineral oil. It can be applied to other insulating liquids in which dissolved gas-in-oil analysis (Test Method D 3612) is commonly performed.

1.2 This test method is particularly suited for detection of the phenomenon sometimes known as "stray gassing" and is also referred to in CIGRE TF11 B39.

1.3 This test method is performed on transformer insulating liquids to determine the propensity of the oil to produce certain gases such as hydrogen and hydrocarbons at low temperatures.

1.4 This test method details two procedures:

1.5 Method A describes the procedure for determining the gassing characteristics of a new, unused insulating liquid, as received, at 120C for 164 h.

1.6 Method B describes the procedure for processing the insulating liquid through an attapulgite clay column to remove organic contaminants and other reactive groups that may influence the gassing behavior of an insulating liquid, which is suspected of being contaminated. This procedure applies to both new and used insulating liquids.

1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and to determine the applicability of regulatory limitations prior to use.