ASTM D3284-05

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:D3284–05
Standard Practice for
Combustible Gases in the Gas Space of Electrical
1
Apparatus Using Portable Meters
This standard is issued under the fixed designation D3284; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope atmosphere. Any combustible gases present are catalytically
oxidized on the surface of a sensor which is an element of a
1.1 Thisfieldpracticecoversthedetectionandestimationof
Wheatstone bridge. When combustible gases oxidize on the
combustible gases in the gas blanket above the oil or in gas
surface, they increase the temperature of the element, which
detector relays in transformers using portable instruments. It is
changes its resistance and upsets the balance of the bridge.
applicable only with transformers using mineral oil as the
3.2 The change in the resistance of the indicating elements
dielectric fluid. Gases dissolved in the oil and noncombustible
in the bridge circuit is indicated on a meter, which is usually
gases are not determined. A method of calibrating the instru-
calibrated to read in percent total combustible gas.
ments with a known gas mixture is included.
1.2 This practice affords a semi-quantitative estimate of the
4. Significance and Use
total combustible gases present in a gas mixture. If a more
4.1 Arcing, partial discharge, and localized overheating in
accurate determination of the total amount of combustible
the insulation system of transformers result in chemical de-
gases or a quantitative determination of the individual compo-
compositionoftheinsulatingoilandotherinsulatingmaterials.
nents is desired, use a laboratory analytical method, such as
This may generate various gases, some of which are combus-
Test Method D3612.
tible. Typically, gases are generated in the oil and then
1.3 This standard does not purport to address all of the
partitioned into the gas space according to their individual
safety concerns, if any, associated with its use. It is the
solubilities. Gases which are highly oil-soluble, such as acety-
responsibility of the user of this standard to establish appro-
lene, may not be in significant quantities in the gas space until
priate safety and health practices and determine the applica-
an incipient fault has progressed to a very serious condition or
bility of regulatory limitations prior to use. Specific precau-
failure of the transformer. Gases such as carbon monoxide and
tionary statements are given in Section 7.
hydrogen which have low solubilities in oil can make up a
2. Referenced Documents large fraction of the combustible gases in the gas space.
2
Detection of these gases is frequently the first available
2.1 ASTM Standards:
indication of a malfunction. Portable combustible gas meters
D3612 Test Method for Analysis of Gases Dissolved in
are a convenient means of detecting the presence of generated
Electrical Insulating Oil by Gas Chromatography
3 gases.
2.2 IEEE Standard:
4.2 Normal operation of a transformer may result in the
C57.104 Guide for the Interpretation of Gases Generated in
formation of some combustible gases. The detection of an
Oil-Immersed Transformers
incipient fault by this method involves an evaluation of the
3. Summary of Practice amount of combustible gases present, the rate of generation of
thesegases,andtheirrateofescapefromthetransformer.Refer
3.1 A sample of gas is diluted to a fixed ratio with air and
to IEEE C57.104 for detailed information on interpretation of
introduced into the meter at a pressure of approximately one
gassing in transformers.
1
This practice is under the jurisdiction of ASTM Committee D27 on Electrical
5. Interferences
Insulating Liquids and Gases and is the direct responsibility of Subcommittee
D27.03 on Analytical Tests. 5.1 In this practice it is essential that sufficient oxygen be
Current edition approved May 1, 2005. Published June 2005. Originally
present in the gas mixture to oxidize the combustible gases.
approved in 1974. Last previous edition approved in 1999 as D3284 – 99. DOI:
Since the gas blanket in a transformer is usually an inert gas, it
10.1520/D3284-05.
2
is necessary to dilute the sample gas with a known amount of
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM air. This is usually accomplished by either introducing air and
Standards volume information, refer to the standard’s Document Summary page on
the sample gas into the instrument in known ratios through
the ASTM website.
fixed orifices, or by mixing known quantities of air and test
3
Available from
...