ASTM D2300-00
(Test Method)Standard Test Method for Gassing of Insulating Liquids Under Electrical Stress and Ionization (Modified Pirelli Method)
Standard Test Method for Gassing of Insulating Liquids Under Electrical Stress and Ionization (Modified Pirelli Method)
SIGNIFICANCE AND USE
For certain applications when insulating liquid is stressed at high voltage gradients, it is desirable to be able to determine the rate of gas evolution or gas absorption under specified test conditions. At present time correlation of such test results with equipment performance is limited.
In this test method, hydrogen (along with low molecular weight hydrocarbons) is generated by ionic bombardment of some insulating liquid molecules and absorbed by chemical reaction with other insulating liquid molecules. The value reported is the net effect of these two competing reactions. The aromatic molecules or unsaturated portions of molecules present in insulating liquids are largely responsible for the hydrogen-absorbing reactions. Both molecule type, as well as concentration, affects the gassing tendency result. Saturated molecules tend to be gas evolving. The relation between aromaticity and quantity of unsaturates of the insulating liquid and gassing tendency is an indirect one and cannot be used for a quantitative assessment of either in the insulating liquid.
This test method measures the tendency of insulating liquids to absorb or evolve gas under conditions of electrical stress and ionization based on the reaction with hydrogen, the predominant gas in the partial discharge. For the test conditions, the activating gas hydrogen, in contrast to other gases, for example, nitrogen, enhances the discrimination of differences in the absorption-evolution patterns exhibited by the insulating liquids. Insulating liquids shown to have gas-absorbing (H2) characteristics in the test have been used to advantage in reducing equipment failures, particularly cables and capacitors. However, the advantage of such insulating liquids in transformers is not well defined and there has been no quantitative relationship established between the gassing tendency as indicated by this test method and the operating performance of the equipment. This test method is not concerned with bubble ...
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1.1 This test method measures the rate at which gas is evolved or absorbed by insulating liquids when subjected to electrical stress of sufficient intensity to cause ionization in cells having specific geometries.
1.2 This test method is not concerned with bubbles arising from supersaturation of the insulating liquid.
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 whoever uses this standard to consult and establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific precautions see 5.1.4 and 8.4.
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Designation: D 2300 – 00
Standard Test Method for
Gassing of Electrical Insulating Liquids Under Electrical
Stress and Ionization (Modified Pirelli Method)
This standard is issued under the fixed designation D 2300; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope volume per unit of time from changes in pressure with time
from two specimens run on the same sample.
1.1 This test method measures the rate at which gas is
3.2 Thistestmethodindicateswhetherinsulatingliquidsare
evolved or absorbed by insulating liquids when subjected to
gas absorbing or gas evolving under the test conditions.
electrical stress of sufficient intensity to cause ionization in
cells having specific geometries.
4. Significance and Use
1.2 This test method is not concerned with bubbles arising
4.1 For certain applications when insulating liquid is
from supersaturation of the insulating liquid.
stressed at high voltage gradients, it is desirable to be able to
1.3 This standard does not purport to address all of the
determine the rate of gas evolution or gas absorption under
safety concerns, if any, associated with its use. It is the
specified test conditions. At present time correlation of such
responsibility of whoever uses this standard to consult and
test results with equipment performance is limited.
establish appropriate safety and health practices and deter-
4.2 Inthistestmethod,hydrogen(alongwithlowmolecular
mine the applicability of regulatory limitations prior to use.
weight hydrocarbons) is generated by ionic bombardment of
For specific precautions see 5.1.4 and 8.4.
some insulating liquid molecules and absorbed by chemical
2. Referenced Documents reaction with other insulating liquid molecules. The value
reportedistheneteffectofthesetwocompetingreactions.The
2.1 ASTM Standards:
aromatic molecules or unsaturated portions of molecules
D924 TestMethodforDissipationFactor(orPowerFactor)
present in insulating liquids are largely responsible for the
and Relative Permittivity (Dielectric Constant) of Electri-
hydrogen-absorbing reactions. Both molecule type, as well as
cal Insulating Liquids
concentration, affects the gassing tendency result. Saturated
3. Summary of Test Method
molecules tend to be gas evolving. The relation between
aromaticity and quantity of unsaturates of the insulating liquid
3.1 After being saturated with a gas (usually hydrogen), the
and gassing tendency is an indirect one and cannot be used for
insulating liquid is subjected to a radial electrical stress. The
a quantitative assessment of either in the insulating liquid.
gas space above the insulating liquid film is ionized due to the
4.3 This test method measures the tendency of insulating
electrical stresses and therefore the insulating liquid surface at
liquids to absorb or evolve gas under conditions of electrical
the insulating liquid-gas interface is subjected to ionic bom-
stress and ionization based on the reaction with hydrogen, the
bardment. The evolving or absorbing of gas is calculated in
predominant gas in the partial discharge. For the test condi-
tions, the activating gas hydrogen, in contrast to other gases,
for example, nitrogen, enhances the discrimination of differ-
This test method is under the jurisdiction of ASTM Committee D27 on
Electrical Insulating Liquids and Gasesand is the direct responsibility of Subcom-
ences in the absorption-evolution patterns exhibited by the
mittee D27.05on Electrical Test.
insulating liquids. Insulating liquids shown to have gas-
Current edition approved Oct. 10, 2000. Published December 2000. Originally
absorbing (H ) characteristics in the test have been used to
published as D2300–68 T. Last previous edition D2300–98.
advantage in reducing equipment failures, particularly cables
Annual Book of ASTM Standards, Vol 10.03.
The original Pirelli method is described by Guiseppe Palandri and Ugo
and capacitors. However, the advantage of such insulating
Pellagatti in the paper. “Gli Oli Isolanti per Cavi Elettrici” (Insulating Oils for
liquids in transformers is not well defined and there has been
Electric Cables), Elettrotecnica (Milan) Jan. 8, 1955. Translation of this paper is
no quantitative relationship established between the gassing
containedin“MinutesoftheMeetingoftheInsulatedConductorsCommitteeofthe
American Institute of Electrical Engineers,” Nov. 15 and 16, 1955. tendency as indicated by this test method and the operating
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D 2300 – 00
performance of the equipment. This test method is not con-
cerned with bubble evolution, which may arise from physical
processes associated with super-saturation of gases in oil or
water vapor bubbles evolving from wet insulation.
5. Apparatus
5.1 The apparatus for making gassing tests where the
insulating liquid is saturated in the same cell that is used
thereafter to electrically stress the insulating liquid is shown in
Fig. 1. The apparatus consists of the following:
5.1.1 Gassing Cell and Buret Assembly, as shown in Fig. 1,
withdimensionsasgiveninFig.2.Thegassingcellconsistsof
the following two components:
5.1.1.1 Cell made of borosilicate glass with the part under
stressconstructedof16mminsidediameterand18mmoutside
diameter truebore tubing. This cell has an outer (ground)
electrode of painted or plated silver with a vertical slit for
observing the insulating liquid level, and a metal conductor
FIG. 2 Detailed Dimensions of the Glass Cell and the Inner (High-
band for ground connection.
Voltage) Electrode
5.1.1.2 Hollow High-Voltage Electrode made of 10 6
0.1-mm outside diameter center-less-ground and polished No.
gassing test cell assembly, and a thermometer graduated in
304 stainless steel seamless tubing and containing an 18-gage
0.1°C divisions. As the test is temperature sensitive, it is
stainless steel capillary tubing as a gas passage. The electrode
importantthatthecalibrationistraceabletoastandard,suchas
shallbesupportedandcenteredbyaprecision-machined24/40
NIST.
recessedTFE-fluorocarbonplug.A ⁄8-in.needlevalve(E)with
5.1.4 Transparent Safety Shield toprotecttheoperatorfrom
gas inlet is on top of the electrode.
contact with high voltage.
5.1.2 Gas Buret (Fig. 1) made of 7-mm outside diameter
5.1.5 High-Voltage Transformer, providing a test voltage
borosilicate glass tubing with an etched scale, tapered glass
having a frequency in the range of 45 to 65 Hz. The
joint (G) for connecting to the gassing cell, a bypass stopcock
transformer and its controlling equipment shall be of such size
(D), and three glass bulbs, (A, B, and C).
anddesignthatwiththetestspecimeninthecircuit,thevoltage
5.1.3 Oil Bath with thermostatic control to maintain the
wave shape shall approximate a sinoid with both half cycles
bath at test temperature 60.5°C. The bath shall be equipped
closely alike. The ratio of peak-to-rms values should be equal
withastirrer,aheatingarrangementcapableofmaintainingthe
to the square root of two within 65 % while maintaining 10
necessary temperature control, a suitable support for the
RV 62%.
6. Reagents and Materials
Suitable equipment is available from Doble Engineering Company, 85 Walnut
6.1 Hydrogen, oxygen-free. See Note 1.
St., Watertown, MA 02472.
6.2 Dibutyl Phthalate, reagent grade.
6.3 2-Propanol, reagent grade.
6.4 Low vapor pressure grease, such as high vacuum
silicone grease.
6.5 Unless otherwise indicated, it is intended that all re-
agents shall conform to the Committee onAnalytical Reagents
of the American Chemical Society.
NOTE 1—Hydrogen normally is the saturating gas but other gases, such
as nitrogen, carbon dioxide, argon, or air may be used.
7. Preparation of Apparatus
7.1 Clean the glass cell by first rinsing it inside and outside
with a suitable hydrocarbon solvent such as heptane or other
solventsuitableforthedielectricliquidtesttested.Thenfillthe
cell with the hydrocarbon solvent and scrub to remove waxy
deposits from previous tests. Clean the tapered joint, taking
care that none of the grease enters the cell. Again rinse with
hydrocarbon solvent and blow dry with clean compressed air.
Check the silver electrode and repair if necessary.
7.2 Clean the hollow electrode by blowing a suitable hy-
FIG. 1 Schematic Diagram of Cell and Manometer Assembly drocarbon solvent through the capillary tube with compressed
D 2300 – 00
air, rinsing the insulating liquid off the entire electrode with a 8.13 To ensure the equipment is operating correctly it is
suitable hydrocarbon solvent, such as heptane, and wiping off recommended that the buret level be read every 10 min until
any waxy deposit with tissue paper. Polish the surface with a thetestisterminated.Aplotofthereadingsversustimeshould
2-propanol soaked towel. If there are visible marks on the give a reasonably straight line. If the data are widely
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