ASTM D2029

Significance and Use

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.

Dew Point		Moisture Content			Dew Point		Moisture Content
°C	°F	lb/1000 ft³	mg/L	volume^A percent	°C	°F	lb/1000 ft³	mg/L	volume^A percent
50	122.0	5.16	82.7	12.2	−16	3.2	0.079	1.27	0.149
49	120.2	4.92	78.9	11.6	−17	1.4	0.072	1.16	0.136
48	118.4	4.69	75.1	11.0	−18	−0.4	0.066	1.06	0.123
47	116.6	4.48	71.9	10.5	−19	−2.2	0.060	0.965	0.112
46	114.8	4.26	68.4	9.95	−20	−4.0	0.055	0.882	0.102
45	113.0	4.06	65.0	9.45	−21	−5.8	0.050	0.809	0.093
44	111.2	3.88	62.1	8.99	−22	−7.6	0.046	0.733	0.084
43	109.4	3.69	59.1	8.52	−23	−9.4	0.042	0.666	0.076
42	107.6	3.52	56.4	8.10	–24	−11.2	0.038	0.608	0.069
41	105.8	3.34	53.5	7.67	−25	−13.0	0.035	0.556	0.063
40	104.0	3.18	50.9	7.27	−26	−14.8	0.031	0.506	0.057
39	102.2	3.02	48.4	6.89	−26	−16.6	0.028	0.454	0.057
38	100.4	2.87	46.0	6.54	−28	−18.4	0.025	0.411	0.046
37	98.6	2.74	43.8	6.20	−29	−20.2	0.023	0.377	0.042
36	96.8	2.60	41.6	5.87	−30	−22.0	0.021	0.343	0.038
35	95.0	2.46	39.4	5.55	−31	−23.8	0.019	0.307	0.034
34	93.2	2.34	37.4	5.25	−32	−25.6	0.017	0.273	0.030
33	91.4	2.22	35.6	4.96	−33	−27.4	0.015	0.246	0.027
32	89.6	2.11	33.8	4.70	−34	−29.2	0.014	0.229	0.025
31	87.8	2.00	32.0	4.44	−35	−31.0	0.013	0.202	0.022
30	86.0	1.89	30.3	4.19	−36	−32.8	0.012	0.185	0.020
29	84.2	1.84	29.2	4.01	−37	−34.6	0.010	0.167	0.018
28	82.4	1.69	27.1	3.7	−38	−36.4	0.0093	0.149	0.016
27	80.6	1.60	25.7	3.52	−39	−38.2	0.0082	0.131	0.014
26	78.8	1.52	24.4	3.33	−40	−40.0	0.0074	0.119	0.0127
25	77.0	1.44	23.0	3.12	−41	−41.8	0.0068	0.107	0.0113
24	75.2	1.35	21.7	2.94	−42	−43.6	0.0060	0.096	0.0102
23	73.4	1.28	20.6	2.78	−43	−45.4	0.0054	0.086	0.0090
22	71.6	1.21	19.4	2.61	−44	−47.2	0.0047	0.076	0.0080
21	69.8	1.14	18.3	2.46	−45	−49.0	0.0042	0.068	0.0071
20	68.0	1.08	17.3	2.31	−46	−50.8	0.0038	0.061	0.0063
19	66.2	1.02	16.3	2.17	−47	−52.6	0.0034	0.054	0.0056
18	64.4	0.961	15.4	2.04	−48	−54.4	0.0031	0.049	0.0050
17	62.6	0.899	14.4	1.91	−49	−56.2	0.0027	0.043	0.0044
16	60.8	0.855	13.7	1.80	−50	−58.0	0.0024	0.038	0.0039
15	59.0	0.799	12.8	1.68	−51	−59.8	0.0021	0.034	0.0034
14	57.2	0.749	12.0	1.57	−52	−61.6	0.0019	0.030	0.0030
13	55.4	0.706	11.3	1.48	−53	−63.4	0.0017	0.027	0.0027
12	53.6	0.668	10.7	1.39	−54	−65.2	0.0014	0.023	0.0023
11	51.8	0.620	9.94	1.29	−55	−67.0	0.0013	0.021	0.0021
10	50.0	0.584	9.37	1.21	−56	−68.8	0.0011	0.018	0.0018
9	48.2	0.547	8.76	1.13	−57	−70.6	0.0010	0.016	0.0016
8	46.4	0.516	8.27	1.06	−58	−72.4	0.00087	0.014	0.0014
7	44.6	0.482	7.73	0.988	−59	−74.2	0.00075	0.012	0.0012
6	42.8	0.452	7.25	0.924	−60	−76.0	0.00069	0.011	0.0011
5	41.0	0.424	6.79	0.861	−61	−77.8	0.00059	0.0095	0.00092
4	39.2	0.399	6.36	0.804	−62	−79.6	0.00052	0.0083	0.00080
3	37.4	0.370	5.94	0.748	−63	−81.4	0.00046	0.0073	0.00070
2	35.6	0.346	5.55	0.696	−64	−83.2	0.00040	0.0064	0.00061
1	33.8	0.323	5.18	0.649	−65	−85.0	0.00035	0.0056	0.00053
0	32.0	0.302	4.84	0.602	−66	−86.8	0.00030	0.0048	0.00045
−1	30.2	0.280	4.49	0.556	−67	−88.6	0.00027	0.0043	0.00040
−2	28.4	0.258	4.14	0.511	−68	−90.4	0.00022	0.0036	0.00034
−3	26.6	0.238	3.81	0.470	−69	−92.2	0.00019	0.0031	0.00029
−4	24.8	0.220	3.52	0.431	−70	−94.0	0.00017	0.0027	0.00025
−5	23.0	0.202	3.24	0.396	−71	−95.8	0.00015	0.0024	0.00022
−6	21.2	0.186	2.98	0.364	−72	−97.6	0.00013	0.0021	0.00019
−7	19.4	0.171	2.74	0.333	−73	−99.4	0.00011	0.0018	0.00016
−8	17.6	0.158	2.53	0.306	−74	−101.2	0.00009	0.0015	0.00014
−9	15.8	0.145	2.32	0.280	−75	−103.0	0.00008	0.0013	0.00012
−10	14.0	0.134	2.14	0.257	−76	−104.8	0.00007	0.0011	0.00010
−11	12.2	0.122	1.96	0.235	−77	−106.6	0.00006	0.0010	0.00009
−12	10.4	0.113	1.81	0.215	−78	−108.4	0.00005	0.0008	0.00007
−13	8.6	0.103	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) The documents listed below are referenced within the subject standard but are not provided as part of the standard. 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 Keywords 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 ICS Code DOI: 10.1520/D2029-97R08 ASTM International is a member of CrossRef. ASTM D2029 (Electrical Insulating Material Standards) Citing ASTM Standards [Back to Top]

ASTM D2029 - 97(2008)

ASTM D2029 - 97(2008) Standard Test Methods for Water Vapor Content of Electrical Insulating Gases by Measurement of Dew Point

ASTM D2029 (Electrical Insulating Material Standards)