ASTM D924-23

Standard Test Method for Dissipation Factor (or Power Factor) and Relative Permittivity (Dielectric Constant) of Electrical Insulating Liquids

SIGNIFICANCE AND USE
4.1 Dissipation Factor (or Power Factor)—This is a measure of the dielectric losses in an electrical insulating liquid when used in an alternating electric field and of the energy dissipated as heat. A low dissipation factor or power factor indicates low ac dielectric losses. Dissipation factor or power factor may be useful as a means of quality control, and as an indication of changes in quality resulting from contamination and deterioration in service or as a result of handling.  
4.1.1 The loss characteristic is commonly measured in terms of dissipation factor (tangent of the loss angle) or of power factor (sine of the loss angle) and may be expressed as a decimal value or as a percentage. For decimal values up to 0.05, dissipation factor and power factor values are equal to each other within about one part in one thousand. In general, since the dissipation factor or power factor of insulating oils in good condition have decimal values below 0.005, the two measurements (terms) may be considered interchangeable.  
4.1.2 The exact relationship between dissipation factor (D) and power factor (PF ) is given by the following equations:
The reported value of D or PF may be expressed as a decimal value or as a percentage. For example:
4.2 Relative Permittivity (Dielectric Constant)—Insulating liquids are used in general either to insulate components of an electrical network from each other and from ground, alone or in combination with solid insulating materials, or to function as the dielectric of a capacitor. For the first use, a low value of relative permittivity is often desirable in order to have the capacitance be as small as possible, consistent with acceptable chemical and heat transfer properties. However, an intermediate value of relative permittivity may sometimes be advantageous in achieving a better voltage distribution of ac electric fields between the liquid and solid insulating materials with which the liquid may be in series. When ...
SCOPE
1.1 This test method describes testing of new electrical insulating liquids as well as liquids in service or subsequent to service in cables, transformers, oil circuit breakers, and other electrical apparatus.  
1.2 This test method provides a procedure for making referee tests at a commercial frequency of between 45 Hz and 65 Hz.  
1.3 Where it is desired to make routine determinations requiring less accuracy, certain modifications to this test method are permitted as described in Sections 16 to 24.  
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.5 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, health, and environmental practices and to determine the applicability of regulatory limitations prior to use. Specific warnings are given in 11.3.3.  
1.6 Mercury has been designated by the EPA and many state agencies as a hazardous material that can cause nervous system, kidney and liver damage. Mercury, or its vapor, may be hazardous to health and corrosive to materials. Caution should be taken when handling mercury and mercury containing products. See the applicable product Safety Data Sheet (SDS) for details and the EPA's website for additional information. Users should be aware that selling mercury and/or mercury containing products into your state may be prohibited by state law.  
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Nov-2023
• ICS: 29.040.10 - Insulating oils
• Technical Committee: D27 - Electrical Insulating Liquids and Gases
• Drafting Committee: D27.05 - Electrical Test

Relations

• Replaces: ASTM D924-15 - Standard Test Method for Dissipation Factor (or Power Factor) and Relative Permittivity (Dielectric Constant) of Electrical Insulating Liquids
• Effective Date: 01-Dec-2023
• Refers: ASTM D923-15(2023) - Standard Practices for Sampling Electrical Insulating Liquids
• Effective Date: 01-Dec-2023
• Refers: ASTM D923-15 - Standard Practices for Sampling Electrical Insulating Liquids
• Effective Date: 01-Oct-2015
• Referred By: ASTM D5282-05(2020) - Standard Test Methods for Compatibility of Construction Material with Silicone Fluid Used for Electrical Insulation
• Effective Date: 01-Dec-2023
• Referred By: ASTM D7826-23b - Standard Guide for Evaluation of New Aviation Gasolines and New Aviation Gasoline Additives
• Effective Date: 01-Dec-2023
• Referred By: ASTM D3394-16(2022) - Standard Test Methods for Sampling and Testing Electrical Insulating Board
• Effective Date: 01-Dec-2023
• Referred By: ASTM D7416-09(2020) - Standard Practice for Analysis of In-Service Lubricants Using a Particular Five-Part (Dielectric Permittivity, Time-Resolved Dielectric Permittivity with Switching Magnetic Fields, Laser Particle Counter, Microscopic Debris Analysis, and Orbital Viscometer) Integrated Tester
• Effective Date: 01-Dec-2023
• Referred By: ASTM D3455-11(2019) - Standard Test Methods for Compatibility of Construction Material with Electrical Insulating Oil of Petroleum Origin
• Effective Date: 01-Dec-2023
• Referred By: ASTM D5222-23 - Standard Specification for Less Flammable High Molecular Weight Hydrocarbon Mineral Electrical Insulating Liquids
• Effective Date: 01-Dec-2023
• Referred By: ASTM D2413-16(2022) - Standard Practice for Preparation of Insulating Paper and Board Impregnated with a Liquid Dielectric
• Effective Date: 01-Dec-2023
• Referred By: ASTM D117-22 - Standard Guide for Sampling, Test Methods, and Specifications for Electrical Insulating Liquids
• Effective Date: 01-Dec-2023
• Referred By: ASTM D3487-16e1 - Standard Specification for Mineral Insulating Oil Used in Electrical Apparatus
• Effective Date: 01-Dec-2023
• Referred By: ASTM D2300-08(2017) - Standard Test Method for Gassing of Electrical Insulating Liquids Under Electrical Stress and Ionization (Modified Pirelli Method)
• Effective Date: 01-Dec-2023
• Referred By: ASTM D4652-20 - Standard Specification for Silicone Liquid Used for Electrical Insulation
• Effective Date: 01-Dec-2023
• Referred By: ASTM D8240-22e1 - Standard Specification for Less-Flammable Synthetic Ester Liquids Used in Electrical Apparatus
• Effective Date: 01-Dec-2023

Overview

ASTM D924-23 is the internationally recognized standard test method for measuring dissipation factor (or power factor) and relative permittivity (dielectric constant) in electrical insulating liquids. Developed by ASTM, this standard provides a unified approach for assessing dielectric losses and insulating properties in new and in-service insulating liquids used in electrical equipment such as cables, transformers, and oil circuit breakers. By establishing precise test procedures and reporting criteria, ASTM D924-23 supports performance verification, quality control, and monitoring of insulation liquids' condition over time.

Key Topics

• Dissipation Factor (Power Factor): This parameter measures dielectric losses in insulating liquids under alternating electric fields and quantifies the energy dissipated as heat. A low dissipation or power factor indicates minimal AC dielectric losses, which is desirable for optimal insulation performance and energy efficiency in electrical equipment.
• Relative Permittivity (Dielectric Constant): This measures the ability of a liquid to store electrical energy in the presence of an electric field. The relative permittivity value influences the overall capacitance and insulation characteristics, making it crucial for both insulation coordination and capacitor design.
• Test Accuracy and Routine Modifications: D924-23 outlines referee test procedures for high-precision situations and provides permissible modifications for routine determinations requiring less accuracy.
• Sampling and Safety: Proper sampling methods are defined to prevent contamination, and important safety considerations are highlighted, including precautions when handling hazardous substances like mercury.
• Reporting Requirements: Detailed criteria for reporting test results ensure consistent industry documentation and traceability.

Applications

The ASTM D924-23 test method is extensively used across the electrical power and equipment industries to:

• Quality Control: Routine and referee testing of insulating liquids for new shipments or before commissioning electrical assets.
• Condition Monitoring: Assessing in-service electrical insulating fluids to detect contamination, moisture ingress, or material deterioration, enabling proactive maintenance and reduction of failure risk.
• Component Design: Selection and validation of insulating liquids for specific applications (e.g., transformers, cables, and capacitors) based on dissipation factor and dielectric constant requirements for optimal operational efficiency and safety.
• Regulatory Compliance: Ensuring insulating liquids meet international standards for dielectric performance, supporting procurement specifications and third-party certification processes.
• Research and Development: Providing a standardized framework for laboratory and field investigations into advanced insulation materials and formulations.

Related Standards

ASTM D924-23 is part of a broader family of standards supporting dielectric property characterization and electrical insulation performance. Key related standards include:

• ASTM D150: Test methods for AC loss characteristics and permittivity (dielectric constant) of solid electrical insulation.
• ASTM D923: Practices for sampling electrical insulating liquids.
• ASTM D2864: Terminology relating to electrical insulating liquids and gases.
• ASTM D2865: Practice for calibration of standards and equipment for electrical insulating materials testing.
• IEEE Standard 4: Standard techniques for high-voltage testing.
• ASTM E691: Practice for conducting interlaboratory studies to determine the precision of a test method.

Practical Value

Implementing ASTM D924-23 ensures reliable, repeatable, and actionable measurements of dissipation factor and dielectric constant, which are critical for maintaining the integrity and efficiency of electrical insulation systems. Regular use of this standard helps prevent costly equipment failures, supports regulatory and procurement requirements, and underpins advancements in electrical insulation technology. By following the detailed procedures in ASTM D924-23, manufacturers, utilities, laboratories, and consultants can confidently verify the quality and performance of insulating liquids, enhancing the reliability of electrical infrastructure globally.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D924 − 23
Standard Test Method for
Dissipation Factor (or Power Factor) and Relative
Permittivity (Dielectric Constant) of Electrical Insulating
Liquids
This standard is issued under the fixed designation D924; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
1.1 This test method describes testing of new electrical
mendations issued by the World Trade Organization Technical
insulating liquids as well as liquids in service or subsequent to
Barriers to Trade (TBT) Committee.
service in cables, transformers, oil circuit breakers, and other
electrical apparatus.
2. Referenced Documents
1.2 This test method provides a procedure for making
2.1 ASTM Standards:
referee tests at a commercial frequency of between 45 Hz and
D150 Test Methods for AC Loss Characteristics and Permit-
65 Hz.
tivity (Dielectric Constant) of Solid Electrical Insulation
1.3 Where it is desired to make routine determinations
D923 Practices for Sampling Electrical Insulating Liquids
requiring less accuracy, certain modifications to this test
D2864 Terminology Relating to Electrical Insulating Liq-
method are permitted as described in Sections 16 to 24.
uids and Gases
D2865 Practice for Calibration of Standards and Equipment
1.4 The values stated in SI units are to be regarded as
for Electrical Insulating Materials Testing
standard. No other units of measurement are included in this
E691 Practice for Conducting an Interlaboratory Study to
standard.
Determine the Precision of a Test Method
1.5 This standard does not purport to address all of the
2.2 IEEE Standard:
safety concerns, if any, associated with its use. It is the
Standard 4 IEEE Standard Techniques for High-Voltage
responsibility of the user of this standard to establish appro-
Testing
priate safety, health, and environmental practices and to
determine the applicability of regulatory limitations prior to
3. Terminology
use. Specific warnings are given in 11.3.3.
1.6 Mercury has been designated by the EPA and many state
3.1 Definitions—Definitions of terms used in this test
agencies as a hazardous material that can cause nervous
method are given in Terminology D2864. Also refer to Test
system, kidney and liver damage. Mercury, or its vapor, may be
Methods D150 for detailed discussion of terms.
hazardous to health and corrosive to materials. Caution should
be taken when handling mercury and mercury containing
4. Significance and Use
products. See the applicable product Safety Data Sheet (SDS)
4.1 Dissipation Factor (or Power Factor)—This is a mea-
for details and the EPA’s website for additional information.
sure of the dielectric losses in an electrical insulating liquid
Users should be aware that selling mercury and/or mercury
when used in an alternating electric field and of the energy
containing products into your state may be prohibited by state
dissipated as heat. A low dissipation factor or power factor
law.
indicates low ac dielectric losses. Dissipation factor or power
1.7 This international standard was developed in accor-
factor may be useful as a means of quality control, and as an
dance with internationally recognized principles on standard-
1 2
This test method is under the jurisdiction of ASTM Committee D27 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Electrical Insulating Liquids and Gases and is the direct responsibility of Subcom- contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
mittee D27.05 on Electrical Test. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Dec. 1, 2023. Published December 2023. Originally the ASTM website.
approved in 1947 as D924 – 47 T. Last previous edition approved in 2015 as Available from Institute of Electrical and Electronic Engineers, 445 Hoes Lane,
D924 – 15. DOI: 10.1520/D0924-23. Piscataway, NJ 08854, www.ieee.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D924 − 23
indication of changes in quality resulting from contamination PROCEDURE FOR MAKING REFEREE TESTS
and deterioration in service or as a result of handling.
6. Apparatus
4.1.1 The loss characteristic is commonly measured in
terms of dissipation factor (tangent of the loss angle) or of
6.1 Measuring equipment used in these procedures shall be
power factor (sine of the loss angle) and may be expressed as
in accordance with Test Methods D150.
a decimal value or as a percentage. For decimal values up to
6.2 Use only a three-terminal cell for these tests.
0.05, dissipation factor and power factor values are equal to
6.3 The design of test cells that conform to the general
each other within about one part in one thousand. In general,
requirements given in the Annex are considered suitable for use
since the dissipation factor or power factor of insulating oils in
in making these tests.
good condition have decimal values below 0.005, the two
measurements (terms) may be considered interchangeable.
6.4 Forced-Draft Oven:
4.1.2 The exact relationship between dissipation factor (D) 6.4.1 When the tests are to be made above room
and power factor (PF ) is given by the following equations: temperature, a suitable forced-draft, thermostatically controlled
oven shall be used as the test chamber. The oven must be
D PF
PF 5 D 5 (1)
capable of meeting the temperature requirements set out in
2 2
=11D =1 2 PF
~ !
Section 11. For tests at room temperature the unheated oven
can be conveniently used as the test chamber.
The reported value of D or PF may be expressed as a
6.4.2 Provide the test chamber with an opening in the wall
decimal value or as a percentage. For example:
through which two lengths of TFE-fluorocarbon-insulated (or
D or PF at 25°C 5 0.002 or 0.2% (2)
similar) shielded cable pass to make electrical connection from
the measuring equipment and high-voltage transformer,
4.2 Relative Permittivity (Dielectric Constant)—Insulating
liquids are used in general either to insulate components of an respectively, to the test cell. Use a perforated ceramic plate or
disk to insulate the test cell from the metal flooring of the oven
electrical network from each other and from ground, alone or
in combination with solid insulating materials, or to function as if the flooring is not insulated from the oven. Provide a safety
the dielectric of a capacitor. For the first use, a low value of interlock on the door of the oven so that the electrical circuit
relative permittivity is often desirable in order to have the supplying voltage to the test cell will be broken when the oven
capacitance be as small as possible, consistent with acceptable door is opened.
chemical and heat transfer properties. However, an intermedi- 6.4.3 A cross-sectional view of the test chamber with a
ate value of relative permittivity may sometimes be advanta- three-electrode test cell in place and with test cables connected
is shown in Fig. 1.
geous in achieving a better voltage distribution of ac electric
fields between the liquid and solid insulating materials with
6.5 Automatic Thermo-Regulator Cell:
which the liquid may be in series. When used as the dielectric
6.5.1 When tests are to be made above room temperature
in a capacitor, it is desirable to have a higher value of relative
but below the flash point, an automatic thermo-regulator cell
permittivity so the physical size of the capacitor may be as
can be used as long as it provides uniform heating of the test
small as possible.
cell.
6.5.2 The automatic thermo-regulator cell must be able to
4.3 Theory relating to dielectric measurement techniques
provide rapid, controlled rate of temperature rise, and be able
and to sources of dielectric loss is given in Test Methods D150.
to maintain a liquid temperature constant to within 61 °C.
5. Sampling
7. Calibration
5.1 Sample electrical insulating liquids in accordance with
7.1 Calibration of test instruments shall be traceable to
Practices D923. Samples to be subjected to this test should
national standards.
preferably be obtained through a closed system. If exposed to
7.2 Verify the calibration at least annually using reference
atmospheric conditions, it is preferable to take the sample
devices that are traceable to national standards.
when the relative humidity is 50 % or less. If it is not feasible,
the length of time the sample is exposed to atmospheric
7.3 Refer to Practice D2865 and IEEE Standard 4 for
conditions must be kept to a minimum.
guidelines on calibrating test equipment.
5.2 Some liquids, in certain applications, require special
8. Test Temperature
handling and processes in the sampling, and these will be
found in the governing procedures. Consult such procedures 8.1 The temperature at which a referee test is made shall be
before samples are taken. mutually agreed upon between the purchaser and the seller.
Measurements are made at many different temperatures. For
5.3 The quantity of sample taken for this test shall be
acceptance tests, it is generally made at a temperature of
sufficient for at least three separate determinations of loss
100 °C, while for routine testing it is usually made at 25 °C,
characteristics and relative permittivity.
90 °C, or 100 °C. In some research investigations, tests may be
5.4 The loss characteristic measurement (dissipation factor made at considerably higher temperatures while in other cases,
or power factor) may be affected by contamination introduced particularly for tests on cable oils in service, tests may be made
during sampling and subsequent handling. over a range of temperatures.
D924 − 23
FIG. 1 Test Set-Up for Dissipation Factor Measurements at Elevated Temperatures Using Three-Electrode Test Cell
9. Test Voltage the inner electrode. As a precaution against this eventuality, use
a suitable stopper to plug this opening prior to starting the
9.1 The average stress to which the specimen is subjected
cleaning operation.
shall not be less than 200 V/mm (5 V/mil) (rms). Tests at higher
stresses are desirable but shall not reach such values that 10.3 After the surfaces of the measuring, guard, and high
electrical discharges across the cell insulating surfaces occur or voltage electrodes have been washed, do not touch these
that internal ionization of the specimen may be expected. surfaces during the rinsing or any subsequent operation.
Stress ranges in normal usage for referee tests are 200 V ⁄mm
10.4 Place the component parts of the test cell in an oven
to 1200 V ⁄mm (5 V ⁄mil to 30 V ⁄mil) (rms).
maintained at 110 °C for a period of not less than 60 min. Do
9.2 Because the ac loss characteristics can vary with voltage not dry test cells made of Monel at this elevated temperature
stress, for reference purposes it is desirable to make the for more than 90 min as oxidation will take place causing
measurements at a specific value of voltage stress within the erroneous results. Take care that the surfaces on which the
limits in 9.1. component parts of the cell are placed in the oven are clean.
9.3 Referee tests should be carried out in the frequency 10.5 At the expiration of the drying period, assemble the
range 45 Hz to 65 Hz. cell using clean cotton gloves as protection for the hands and
to prevent contamination from skin oils and salt.
10. Cleaning Test Cell
11. Preparation of Specimen and Filling Test Cell
10.1 The cleanliness of the test cell is of paramount impor-
tance when measuring loss characteristics because of the 11.1 Store the sample in its original sealed container,
inherent susceptibility of most insulating liquids to contami- shielded from light. Some liquids, such as oils of petroleum
nating influences of the most minute nature. For this reason, origin, undergo changes when exposed to sunlight. Allow the
clean and dry the cell immediately prior to making the test, and sealed container to stand undisturbed in the room in which the
strictly observe the procedures and precautions outlined in 10.2 test is to be made for a sufficient period of time to permit the
to 10.5. sample to attain room temperature before it is opened.
10.2 Dismantle the cell completely and wash all the com- 11.2 When insulating liquids are heated to elevated
ponent parts thoroughly with a technical grade of a suitable temperatures, some of their characteristics undergo a change
solvent (such as acetone, pentane, petroleum ether, or heptane). with time and the change, even though of the minutest nature,
Wash the component parts with a mild abrasive soap or may be reflected in the loss measurement. It is therefore
detergent. Take care not to lay the electrodes on any surface. desirable that the elapsed time necessary for the test specimen
Rinse all parts thoroughly with hot tap water, then with cold tap to attain temperature equilibrium with the test cell be held to a
water, followed by several rinses with distilled water. Take minimum. For optimum procedure do not exceed 20 min for
extreme care during the washing and rinsing of some test cells this time. It is essential, therefore, that the procedures outlined
to prevent any moisture from entering the thermometer well in below be closely followed.
D924 − 23
11.3 Forced-Draft Oven: refill the cell and take a third measurement. If the difference
11.3.1 In order that representative test specimens may be between the third measurement and either the first or second is
obtained, gently tilt or invert the sample container and swirl the not within 0.0001, plus 10 % of the higher of the two values
liquid several times. Immediately after mixing the sample, pour used in this computation, discard these results, reclean the cell,
a quantity of liquid sufficient for four fillings of the test cell obtain another sample, and repeat the procedure until two
into a chemically clean dry beaker and heat on a hot plate to a measurements from a sample are obtained that do meet the
temperature 2 °C below the desired test temperature. Stir the prescribed limits.
fluid frequently during heating.
11.3.2 Remove the cell from the test chamber, lift out the 13. Procedure—Relative Permittivity
inner electrode, but do not rest it on any surface, and fill the cell
13.1 Measure the capacitance of the test cell with air as the
with a portion of the heated specimen. Replace the beaker with
dielectric and then with the cell filled with the liquid. Both
the remainder of the heated sample on the hot plate. Insert the
measurements should be made at the same temperature. Use
inner electrode and rinse the electrodes by twice raising and
these measurements in calculating the relative permittivity
lowering the inner electrode. Remove the inner electrode and
from the following equation:
hold it suspended in air; then decant the rinsing liquid and
K' 5 C /C (3)
x v
immediately fill the cell from the remainder of the heated
specimen. Replace the inner electrode.
where:
11.3.3 Insert a mercury thermometer graduated in 0.25 °C
K' = relative permittivity of the liquid,
increments, or other temperature measuring devices (for
C = capacitance of test cell with the liquid as the dielectric,
x
example, thermocouples) that provide equal accuracy, in the
and
thermometer well provided in the inner electrode
C = capacitance of test cell with air as the dielectric.
v
(Warning—A spring-loaded thermocouple may be used for
measuring the temperature of the inner electrode, but extreme
14. Report
caution shall be exercised that these wires do not come in
14.1 Report the following informatio
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D924 − 15 D924 − 23
Standard Test Method for
Dissipation Factor (or Power Factor) and Relative
Permittivity (Dielectric Constant) of Electrical Insulating
Liquids
This standard is issued under the fixed designation D924; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope
1.1 This test method describes testing of new electrical insulating liquids as well as liquids in service or subsequent to service in
cables, transformers, oil circuit breakers, and other electrical apparatus.
1.2 This test method provides a procedure for making referee tests at a commercial frequency of between 45 and 65 Hz.45 Hz and
65 Hz.
1.3 Where it is desired to make routine determinations requiring less accuracy, certain modifications to this test method are
permitted as described in Sections 16 to 24.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 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 healthsafety, health, and environmental practices and to determine
the applicability of regulatory limitations prior to use. Specific warnings are given in 11.3.3.
1.6 Mercury has been designated by the EPA and many state agencies as a hazardous material that can cause nervous system,
kidney and liver damage. Mercury, or its vapor, may be hazardous to health and corrosive to materials. Caution should be taken
when handling mercury and mercury containing products. See the applicable product Material Safety Data Sheet (MSDS)(SDS)
for details and the EPA’s website: http://www.epa.gov/mercury/faq.htm website for additional information. Users should be aware
that selling mercury and/or mercury containing products into your state may be prohibited by state law.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D150 Test Methods for AC Loss Characteristics and Permittivity (Dielectric Constant) of Solid Electrical Insulation
This test method is under the jurisdiction of ASTM Committee D27 on Electrical Insulating Liquids and Gases and is the direct responsibility of Subcommittee D27.05
on Electrical Test.
Current edition approved Oct. 1, 2015Dec. 1, 2023. Published November 2015December 2023. Originally approved in 1947 as D924 – 47 T. Last previous edition approved
in 20082015 as D924 – 08.D924 – 15. DOI: 10.1520/D0924-15.10.1520/D0924-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D924 − 23
D923 Practices for Sampling Electrical Insulating Liquids
D2864 Terminology Relating to Electrical Insulating Liquids and Gases
D2865 Practice for Calibration of Standards and Equipment for Electrical Insulating Materials Testing
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
2.2 IEEE Standard:
Standard 4 IEEE Standard Techniques for High-Voltage Testing
3. Terminology
3.1 Definitions—Definitions of terms used in this test method are given in Terminology D2864. Also refer to Test Methods D150
for detailed discussion of terms.
4. Significance and Use
4.1 Dissipation Factor (or Power Factor)—This is a measure of the dielectric losses in an electrical insulating liquid when used
in an alternating electric field and of the energy dissipated as heat. A low dissipation factor or power factor indicates low ac
dielectric losses. Dissipation factor or power factor may be useful as a means of quality control, and as an indication of changes
in quality resulting from contamination and deterioration in service or as a result of handling.
4.1.1 The loss characteristic is commonly measured in terms of dissipation factor (tangent of the loss angle) or of power factor
(sine of the loss angle) and may be expressed as a decimal value or as a percentage. For decimal values up to 0.05, dissipation
factor and power factor values are equal to each other within about one part in one thousand. In general, since the dissipation factor
or power factor of insulating oils in good condition have decimal values below 0.005, the two measurements (terms) may be
considered interchangeable.
4.1.2 The exact relationship between dissipation factor (D) and power factor (PF ) is given by the following equations:
D PF
PF 5 D 5 (1)
2 2
=11D =12 PF
~ !
The reported value of D or PF may be expressed as a decimal value or as a percentage. For example:
D or PF at 25°C 5 0.002 or 0.2% (2)
4.2 Relative Permittivity (Dielectric Constant)—Insulating liquids are used in general either to insulate components of an electrical
network from each other and from ground, alone or in combination with solid insulating materials, or to function as the dielectric
of a capacitor. For the first use, a low value of relative permittivity is often desirable in order to have the capacitance be as small
as possible, consistent with acceptable chemical and heat transfer properties. However, an intermediate value of relative
permittivity may sometimes be advantageous in achieving a better voltage distribution of ac electric fields between the liquid and
solid insulating materials with which the liquid may be in series. When used as the dielectric in a capacitor, it is desirable to have
a higher value of relative permittivity so the physical size of the capacitor may be as small as possible.
4.3 Theory relating to dielectric measurement techniques and to sources of dielectric loss is given in Test Methods D150.
5. Sampling
5.1 Sample electrical insulating liquids in accordance with Practices D923. Samples to be subjected to this test should preferably
be obtained through a closed system. If exposed to atmospheric conditions, it is preferable to take the sample when the relative
humidity is 50 % or less. If it is not feasible, the length of time the sample is exposed to atmospheric conditions must be kept to
a minimum.
5.2 Some liquids, in certain applications, require special handling and processes in the sampling, and these will be found in the
governing procedures. Consult such procedures before samples are taken.
5.3 The quantity of sample taken for this test shall be sufficient for at least three separate determinations of loss characteristics
and relative permittivity.
Available from Institute of Electrical and Electronic Engineers, 445 Hoes Lane, Piscataway, NJ 08854, www.ieee.org.
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5.4 The loss characteristic measurement (dissipation factor or power factor) may be affected by contamination introduced during
sampling and subsequent handling.
PROCEDURE FOR MAKING REFEREE TESTS
6. Apparatus
6.1 Measuring equipment used in these procedures shall be in accordance with Test Methods D150.
6.2 Use only a three-terminal cell for these tests.
6.3 The design of test cells that conform to the general requirements given in the Annex are considered suitable for use in making
these tests.
6.4 Forced-Draft Oven:
6.4.1 When the tests are to be made above room temperature, a suitable forced-draft, thermostatically controlled oven shall be used
as the test chamber. The oven must be capable of meeting the temperature requirements set out in Section 11. For tests at room
temperature the unheated oven can be conveniently used as the test chamber.
6.4.2 Provide the test chamber with an opening in the wall through which two lengths of TFE-fluorocarbon-insulated (or similar)
shielded cable pass to make electrical connection from the measuring equipment and high-voltage transformer, respectively, to the
test cell. Use a perforated ceramic plate or disk to insulate the test cell from the metal flooring of the oven if the flooring is not
insulated from the oven. Provide a safety interlock on the door of the oven so that the electrical circuit supplying voltage to the
test cell will be broken when the oven door is opened.
6.4.3 A cross-sectional view of the test chamber with a three-electrode test cell in place and with test cables connected is shown
in Fig. 1.
6.5 Automatic Thermo-Regulator Cell:
FIG. 1 Test Set-Up for Dissipation Factor Measurements at Elevated Temperatures Using Three-Electrode Test Cell
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6.5.1 When tests are to be made above room temperature but below the flash point, an automatic thermo-regulator cell can be used
as long as it provides uniform heating of the test cell.
6.5.2 The automatic thermo-regulator cell must be able to provide rapid, controlled rate of temperature rise, and be able to
maintain a liquid temperature constant to within 61°C.61 °C.
7. Calibration
7.1 Calibration of test instruments shall be traceable to national standards.
7.2 Verify the calibration at least annually using reference devices that are traceable to national standards.
7.3 Refer to Practice D2865 and IEEE Standard 4 for guidelines on calibrating test equipment.
8. Test Temperature
8.1 The temperature at which a referee test is made shall be mutually agreed upon between the purchaser and the seller.
Measurements are made at many different temperatures. For acceptance tests, it is generally made at a temperature of
100°C,100 °C, while for routine testing it is usually made at 25, 90 or 100°C.25 °C, 90 °C, or 100 °C. In some research
investigations, tests may be made at considerably higher temperatures while in other cases, particularly for tests on cable oils in
service, tests may be made over a range of temperatures.
9. Test Voltage
9.1 The average stress to which the specimen is subjected shall not be less than 200 V/mm (5 V/mil) (rms). Tests at higher stresses
are desirable but shall not reach such values that electrical discharges across the cell insulating surfaces occur or that internal
ionization of the specimen may be expected. Stress ranges in normal usage for referee tests are 200200 V ⁄mm to 12001200 V
V/mm⁄mm (5 V (5 to 30⁄mil to 30 V V/mil) ⁄mil) (rms).
9.2 Because the ac loss characteristics can vary with voltage stress, for reference purposes it is desirable to make the measurements
at a specific value of voltage stress within the limits in 9.1.
9.3 Referee tests should be carried out in the frequency range 45–65 45 Hz to 65 Hz.
10. Cleaning Test Cell
10.1 The cleanliness of the test cell is of paramount importance when measuring loss characteristics because of the inherent
susceptibility of most insulating liquids to contaminating influences of the most minute nature. For this reason, clean and dry the
cell immediately prior to making the test, and strictly observe the procedures and precautions outlined in 10.2 to 10.5.
10.2 Dismantle the cell completely and wash all the component parts thoroughly with a technical grade of a suitable solvent (such
as acetone, pentane, petroleum ether, or heptane). Wash the component parts with a mild abrasive soap or detergent. Take care not
to lay the electrodes on any surface. Rinse all parts thoroughly with hot tap water, then with cold tap water, followed by several
rinses with distilled water. Take extreme care during the washing and rinsing of some test cells to prevent any moisture from
entering the thermometer well in the inner electrode. As a precaution against this eventuality, use a suitable stopper to plug this
opening prior to starting the cleaning operation.
10.3 After the surfaces of the measuring, guard, and high voltage electrodes have been washed, do not touch these surfaces during
the rinsing or any subsequent operation.
10.4 Place the component parts of the test cell in an oven maintained at 110°C110 °C for a period of not less than 60 min. 60 min.
Do not dry test cells made of Monel at this elevated temperature for more than 90 min as oxidation will take place causing
erroneous results. Take care that the surfaces on which the component parts of the cell are placed in the oven are clean.
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10.5 At the expiration of the drying period, assemble the cell using clean cotton gloves as protection for the hands and to prevent
contamination from skin oils and salt.
11. Preparation of Specimen and Filling Test Cell
11.1 Store the sample in its original sealed container, shielded from light. Some liquids, such as oils of petroleum origin, undergo
changes when exposed to sunlight. Allow the sealed container to stand undisturbed in the room in which the test is to be made
for a sufficient period of time to permit the sample to attain room temperature before it is opened.
11.2 When insulating liquids are heated to elevated temperatures, some of their characteristics undergo a change with time and
the change, even though of the minutest nature, may be reflected in the loss measurement. It is therefore desirable that the elapsed
time necessary for the test specimen to attain temperature equilibrium with the test cell be held to a minimum. For optimum
procedure do not exceed 20 min for this time. It is essential, therefore, that the procedures outlined below be closely followed.
11.3 Forced-Draft Oven:
11.3.1 In order that representative test specimens may be obtained, gently tilt or invert the sample container and swirl the liquid
several times. Immediately after mixing the sample, pour a quantity of liquid sufficient for four fillings of the test cell into a
chemically clean dry beaker and heat on a hot plate to a temperature 2°C2 °C below the desired test temperature. Stir the fluid
frequently during heating.
11.3.2 Remove the cell from the test chamber, lift out the inner electrode, but do not rest it on any surface, and fill the cell with
a portion of the heated specimen. Replace the beaker with the remainder of the heated sample on the hot plate. Insert the inner
electrode and rinse the electrodes by twice raising and lowering the inner electrode. Remove the inner electrode and hold it
suspended in air; then decant the rinsing liquid and immediately fill the cell from the remainder of the heated specimen. Replace
the inner electrode.
11.3.3 Insert a mercury thermometer graduated in 0.25°C0.25 °C increments, or other temperature measuring devices (for
example, thermocouples) that provide equal accuracy, in the thermometer well provided in the inner electrode (Warning—
WarningA—A spring-loaded thermocouple may be used for measuring the temperature of the inner electrode, but extreme caution
shall be exercised that these wires do not come in contact with the high-voltage lead and do not pick up stray emfs). Immediately
return the filled cell to the test chamber (adjusted to a temperature above the desired test temperature) and make the necessary
electrical connections to the cell.
11.3.4 Perform the operations described in 11.3.2 and 11.3.3 as rapidly as possible.
11.4 Automatic Thermo-Regulator Cell:
11.4.1 Gently swirl or invert the sample container to obtain a representative test specimen.
11.4.2 Fill the test cell and flush to rinse thoroughly both the inner and outer electrodes with a portion of the sample. Decant the
rinsing liquid and immediately fill the cell with a new aliquot of sample.
11.4.3 Replace inner electrode and make all necessary electrical connections to the cell. On some instruments the cell must be in
place before filling with specimen.
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