ASTM D2029-26

1.1 These test methods describe the determination of the water vapor content of electrical insulating gases by directly or indirectly measuring the dew point and calculating the water vapor content.

1.2 The following three test methods are provided:

1.3 This standard will also provide insight into the direct measurement of dew point in electrical insulating gas from in-field servicing of various gas insulating equipment.

1.4 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. For specific warnings, see 8.1.1, 9.2, and 10.1.2.

1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

5.1 Certain gases have excellent dielectric and electric arc interruption characteristics, making their use in electrical installations desirable.

5.2 Water content, as the test parameter, is important in determining the gas's dielectric effectiveness. Under certain conditions, water may condense and become a conducting liquid, breaking down the gas’s dielectric properties. The water content of these insulating gases, as expressed by dew point, is listed in Specifications D1933, D2472, and D3283.

5.3 Once the dew point is determined, Table 1 may be used to convert it into moisture content. Once moisture content is known, the lowest temperature at which gas-insulated equipment can be safely operated is typically determined by reviewing the equipment's specifications.

5.4 The dew point of the test gas is independent of the gas temperature but does depend on its pressure. Many moisture measurement test instruments are sensitive to pressure, and display moisture values at the instrument inlet pressure and not necessarily at the pressure of the sampled system. It is, therefore, important to account for this condition to avoid serious measurement errors.