ASTM D6786-02
(Test Method)Standard Test Method for Particle Count in Mineral Insulating Oil Using Automatic Optical Particle Counters
Standard Test Method for Particle Count in Mineral Insulating Oil Using Automatic Optical Particle Counters
SIGNIFICANCE AND USE
Particles in insulating oil can have a detrimental effect on the dielectric properties of the fluid, depending on the size, concentration, and nature of the particles. The source of these particles can be external contaminants, oil degradation by-products, or internal materials such as metals, carbon, or cellulose fibers.
Particle counts provide a general degree of contamination level and may be useful in accessing the condition of specific types of electrical equipment. Particle counts can also be used to determine filtering effectiveness when processing oil.
If more specific knowledge of the nature of the particles is needed, other tests such as metals analysis or fiber identification and counting must be performed.
SCOPE
1.1 This test method covers the determination of particle concentration and particle size distribution in mineral insulating oil. It is suitable for testing oils having a viscosity of 6 to 20 cSt at 40°C. The test method is specific to liquid automatic particle analyzers that use the light extinction principle.
1.2 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.
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Designation:D6786–02
Standard Test Method for
Particle Count in Mineral Insulating Oil Using Automatic
Optical Particle Counters
This standard is issued under the fixed designation D 6786; 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 is determined by the maximum acceptable concentration of
particles in the given sample and is supplied by the instrument
1.1 This test method covers the determination of particle
manufacturer.
concentration and particle size distribution in mineral insulat-
3.1.3 electronic saturation level—particle concentration at
ing oil. It is suitable for testing oils having a viscosity of 6 to
whichtheelectroniccircuitryoftheanalyzerceasestofunction
20 cSt at 40°C. The test method is specific to liquid automatic
properly due to excessive counting rates.
particle analyzers that use the light extinction principle.
3.1.4 light extinction—the reduction in intensity of a light
1.2 This standard does not purport to address all of the
beam passing through the sensing zone of a particle analyzer,
safety concerns, if any, associated with its use. It is the
caused by the absorption and/or scattering of the light by
responsibility of the user of this standard to establish appro-
particles. Synonyms: light obscuration, light interruption, light
priate safety and health practices and determine the applica-
blockage.
bility of regulatory limitations prior to use.
4. Summary of Test Method
2. Referenced Documents
4.1 Samples are taken in particle-clean bottles that are
2.1 ASTM Standards:
dedicated to particle analysis. The sample bottle is agitated to
D 923 Practices for Sampling Electrical Insulating Liquids
redistribute particles in the oil, then immediately placed in an
2.2 ISO Standards:
automatic particle counter, where the number of particles and
4406:1999 Hydraulic Fluid Power—Fluids—Method for
their size distribution are determined by the light extinction
Coding the Level of Contamination by Solid Particles
principle.
11171:1999 Hydraulic Fluid Power—Calibration of Auto-
4.2 As particles pass through the sensing zone of the
matic Particle Counters for Liquids
instrument, the quantity of light reaching the detector is
3. Terminology obscured. This signal is translated to an equivalent projected
area diameter based on calibration with a NIST-traceable fluid
3.1 Definitions:
(ISO Medium Test Dust suspension).
3.1.1 coincidence—the presence of more than one particle
in the sensing zone of a particle analyzer at the same time,
5. Significance and Use
causing mis-sizing and mis-counting of the particle present.
5.1 Particles in insulating oil can have a detrimental effect
The coincidence limit of the counter is determined by the
on the dielectric properties of the fluid, depending on the size,
maximum acceptable concentration of particles in the sensing
concentration, and nature of the particles. The source of these
zone and is supplied by the instrument manufacturer.
particles can be external contaminants, oil degradation by-
3.1.2 concentration limit—a direct function of coincidence
products, or internal materials such as metals, carbon, or
and electronic saturation.The concentration limit of the system
cellulose fibers.
5.2 Particle counts provide a general degree of contamina-
This test method is under the jurisdiction of ASTM Committee D27 on
tion level and may be useful in accessing the condition of
Electrical Insulating Liquids and Gases and is the direct responsibility of Subcom-
specific types of electrical equipment. Particle counts can also
mittee D27.07 on Physical Tests.
be used to determine filtering effectiveness when processing
Current edition approved April 10, 2002. Published June 2002.
oil.
Annual Book of ASTM Standards, Vol 10.03.
Available from American National Standards Institute, 11 West 42nd Street,
New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6786–02
5.3 If more specific knowledge of the nature of the particles 9. Sampling
is needed, other tests such as metals analysis or fiber identifi-
9.1 Refer to Practice D 923 for precautions for sampling
cation and counting must be performed.
from energized electrical equipment.
9.2 Proper sampling is crucial to particulate analysis. The
6. Interferences
following guidelines are offered to ensure representative sam-
6.1 Dirty environmental conditions and poor handling tech-
pling and to preserve sample integrity:
niques can easily contaminate the sample and/or test specimen.
9.2.1 Wipe the sample port outlet with a clean lint-free
Care must be taken to ensure test results are not biased by
towel. Open the sample valve and flush about 3 times the flow
introduced particles.
path volume of oil into a container.
6.2 Air bubbles in the oil may be counted as particles giving
9.2.2 While flushing, uncap the sample bottle and retain the
false positive readings. Mixing or agitating the sample intro-
cap in one hand and the bottle in the other. Without adjusting
duces bubbles into the oil, but these readily dissipate and
thevalveordisturbingsampleflow,fillthebottletoabout80 %
generally do not interfere with insulating oil particle counts.
capacity. Do not completely fill the bottle since the headspace
6.3 Suspended or free water in the oil will generally be
will be needed for sample agitation.
counted as particles. Normally, free water concentration
...
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