ASTM D3284-99

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Designation:D3284–99
Standard Test Method for
Combustible Gases in the Gas Space of
Electrical Apparatus Using Portable Meters
This standard is issued under the fixed designation D 3284; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope surface, they increase the temperature of the element, which
changes its resistance and upsets the balance of the bridge.
1.1 This field test method covers the detection and estima-
3.2 The change in the resistance of the indicating elements
tion of combustible gases in the gas blanket above the oil or in
in the bridge circuit is indicated on a meter, which is usually
gas detector relays in transformers using portable instruments.
calibrated to read in percent total combustible gas.
It is applicable only with transformers using mineral oil as the
dielectric fluid. Gases dissolved in the oil and noncombustible
4. Significance and Use
gases are not determined. A method of calibrating the instru-
4.1 Arcing, partial discharge, and localized overheating in
ments with a known gas mixture is included.
the insulation system of transformers result in chemical de-
1.2 This test method affords a semi-quantitative estimate of
compositionoftheinsulatingoilandotherinsulatingmaterials.
the total combustible gases present in a gas mixture. If a more
This may generate various gases, some of which are combus-
accurate determination of the total amount of combustible
tible. Typically, gases are generated in the oil and then
gases or a quantitative determination of the individual compo-
partitioned into the gas space according to their individual
nents is desired, use a laboratory analytical method, such as
solubilities. Gases which are highly oil-soluble, such as acety-
Test Method D 3612.
lene, may not be in significant quantities in the gas space until
1.3 This standard does not purport to address all of the
an incipient fault has progressed to a very serious condition or
safety concerns, if any, associated with its use. It is the
failure of the transformer. Gases such as carbon monoxide and
responsibility of the user of this standard to establish appro-
hydrogen which have low solubilities in oil can make up a
priate safety and health practices and determine the applica-
large fraction of the combustible gases in the gas space.
bility of regulatory limitations prior to use. Specific precau-
Detection of these gases is frequently the first available
tionary statements are given in Section 7.
indication of a malfunction. Portable combustible gas meters
2. Referenced Documents are a convenient means of detecting the presence of generated
gases.
2.1 ASTM Standards:
4.2 Normal operation of a transformer may result in the
D 3612 Test Method for Analysis of Gases Dissolved in
formation of some combustible gases. The detection of an
Electrical Insulating Oil by Gas Chromatography
incipient fault by this method involves an evaluation of the
2.2 IEEE Standard:
amount of combustible gases present, the rate of generation of
C57.104 Guide for the Interpretation of Gases Generated in
3 thesegases,andtheirrateofescapefromthetransformer.Refer
Oil-Immersed Transformers
to IEEE C57.104 for detailed information on interpretation of
3. Summary of Test Method gassing in transformers.
3.1 A sample of gas is diluted to a fixed ratio with air and
5. Interferences
introduced into the meter at a pressure of approximately one
5.1 In this test method it is essential that sufficient oxygen
atmosphere. Any combustible gases present are catalytically
be present in the gas mixture to oxidize the combustible gases.
oxidized on the surface of a sensor which is an element of a
Since the gas blanket in a transformer is usually an inert gas, it
Wheatstone bridge. When combustible gases oxidize on the
is necessary to dilute the sample gas with a known amount of
air. This is usually accomplished by either introducing air and
This test method is under the jurisdiction of ASTM Committee D-27 on
the sample gas into the instrument in known ratios through
Electrical Insulating Liquids and Gases and is the direct responsibility of Subcom-
fixed orifices, or by mixing known quantities of air and test
mittee D27.03on Analytical Tests.
specimen externally by displacement over water before intro-
Current edition approved April 10, 1999. Published June 1999. Originally
duction into the instrument. The working range of these
published as D 3284 – 74. Last previous edition D 3284 – 90a (1994).
Annual Book of ASTM Standards, Vol 10.03.
instruments is between the low limit of sensitivity and about
Available from IEEE, 445 Hoes Lane, Piscataway, NJ 08855-1331.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D3284
the lower explosive limit. They generally read off-scale at the air and reference gas mixture is being tested. Purge the meter
high end between the lower explosive limit and the upper with air to remove traces of reference gas and proceed in
explosive limit and may indicate zero when the combustible accordance with Section 9.
gas content is above the upper explosive limit.
9. Procedure
5.2 Contamination of the sensor can seriously impair the
9.1 Prepare the instrument for operation in accordance with
sensitivity and response of the meter. This loss of response
the instrument manufacturer’s instructions. This may include a
does not affect the normal balancing of the bridge circuit, an
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