ASTM D2029 Standard Test Methods for Water Vapor Content of Electrical Insulating Gases by Measurement of Dew Point
ASTM D2029用露點法測定電絕緣氣體中水蒸汽含量試驗方法
Certain gases have excellent dielectric and electric arc interruption characteristics which make their use in electrical installations very desirable.
Water content, as the test parameter, is of great importance in determining the dielectric effectiveness of the gas. Under certain conditions, water may condense and become a conducting liquid resulting in a catastrophic dielectric breakdown of the insulation. The water content of these insulating gases as expressed by dew point is listed in Specifications D 1933, D 2473, and D 3283.
Once the dew point is determined, a conversion to moisture content may be performed using Table 1. Once moisture content is known, the lowest temperature at which gas insulated equipment can be safely operated can usually be determined by reviewing manufacturers' specifications for the equipment.
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 system being sampled. It is therefore important to account for this condition to avoid serious measurement errors.
TABLE 1 Relationship Between Dew Point and Moisture Content of Gases
Note—With a known dew point which is indicated by the dew point indicator or recorder, the moisture content can be read directly from the table. The table shows the amount of water in air or other gas at various dew points at a pressure of 1 atm (14.7) psi.
1. Scope
1.1 These test methods describe the determination of the water vapor content of electrical insulating gases by direct or indirect measurement of the dew point and the calculation of the
water vapor content.
1.2 The following four test methods are provided:
1.2.1 Method A describes the automatic chilled mirror method for measurement of dew point
as low as − 73°C (−99°F).
1.2.2 Method B describes the manual chilled mirror or dew cup method for measurement of
dew point as low as − 73°C (−99°F).
1.2.3 Method C describes the adiabatic expansion method for measurement of dew point as
low as − 62°C (−80°F).
1.2.4 Method D describes the capacitance method for measurement of dew point as low as −
110°C (−166°F).
1.3 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 determine the applicability of regulatory limitations prior to use. For specific warnings, see 8.1.1, 9.2, 10.1.2 and 10.2.5.
2. Referenced Documents (purchase separately)
ASTM Standards
D1933 Specification for Nitrogen Gas as an Electrical Insulating Material
D2472 Specification for Sulfur Hexafluoride
D3283 Specification for Air as an Electrical Insulating Material
D2472 Specification for Sulfur Hexafluoride
D3283 Specification for Air as an Electrical Insulating Material
Index Terms
adiabatic expansion; aluminum oxide; chilled mirror; condensation; dew point; electrical insulating gas; fog; hygrometer; moisture content; SF6; silicon oxide; water vapor content; Dew/frost point; Electrical insulating gases; Water vapor content
