ASTM D3284-05(2011)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: D3284 − 05 (Reapproved 2011)
Standard Practice for
Combustible Gases in the Gas Space of Electrical
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
dielectric fluid. Gases dissolved in the oil and noncombustible
3.2 The change in the resistance of the indicating elements
gases are not determined. A method of calibrating the instru-
in the bridge circuit is indicated on a meter, which is usually
ments with a known gas mixture is included.
calibrated to read in percent total combustible gas.
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
gases or a quantitative determination of the individual compo- the insulation system of transformers result in chemical de-
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
responsibility of the user of this standard to establish appro-
acetylene, may not be in significant quantities in the gas space
priate safety and health practices and determine the applica-
until an incipient fault has progressed to a very serious
bility of regulatory limitations prior to use. Specific precau-
condition or failure of the transformer. Gases such as carbon
tionary statements are given in Section 7.
monoxide and hydrogen which have low solubilities in oil can
2. Referenced Documents
make up a large fraction of the combustible gases in the gas
space. 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
gases.
2.2 IEEE Standard:
C57.104 Guide for the Interpretation of Gases Generated in
4.2 Normal operation of a transformer may result in the
Oil-Immersed Transformers
formation of some combustible gases. The detection of an
incipient fault by this method involves an evaluation of the
3. Summary of Practice
amount of combustible gases present, the rate of generation of
3.1 A sample of gas is diluted to a fixed ratio with air and
thesegases,andtheirrateofescapefromthetransformer.Refer
introduced into the meter at a pressure of approximately one
to IEEE C57.104 for detailed information on interpretation of
gassing in transformers.
This practice is under the jurisdiction of ASTM Committee D27 on Electrical
Insulating Liquids and Gasesand is the direct responsibility of Subcommittee
5. Interferences
D27.03 on Analytical Tests.
Current edition approved May 1, 2011. Published June 2011. Originally
5.1 In this practice it is essential that sufficient oxygen be
approved in 1974. Last previous edition approved in 2005 as D3284 – 05. DOI:
present in the gas mixture to oxidize the combustible gases.
10.1520/D3284-05R11.
Since the gas blanket in a transformer is usually an inert gas, it
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
is necessary to dilute the sample gas with a known amount of
Standards volume information, refer to the standard’s Document Summary page on
air. This is usually accomplished by either introducing air and
the ASTM website.
the sample gas into the instrument in known ratios through
Available from Institute of Electrical and Electronics Engineers, Inc. (IEEE),
445 Hoes Ln., P.O. Box 1331, Piscataway, NJ 08854-1331, http://www.ieee.org. fixed orifices, or by mixing known quantities of air and test
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D3284 − 05 (2011)
specimen externally by displacement over water before intro- 8.3 Turn the calibration adjustment so the meter indicates
duction into the instrument. The working range of these the known methane content of the reference standard when the
instruments is between the low limit of sensitivity and about air and reference gas mixture is being tested. Purge the meter
the lower explosive limit. They generally read off-scale at the with air to remove traces of reference gas and proceed in
high end between the lower explosive limit and the upper accordance with Section 9.
explosive limit and may indicate zero when the combustible
9. Procedure
gas content is above the upper explosive limit.
9.1 Prepare the instrument for operation in accordance with
5.2 Contamination of the sensor can seriously impair the
the instrument manufacturer’s instructions. This may include a
sensitivity and response of the meter. This loss of response
warm-up period to
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