ASTM D149-20

Standard Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials at Commercial Power Frequencies

SIGNIFICANCE AND USE
5.1 The dielectric strength of an electrical insulating material is a property of interest for any application where an electrical field will be present. In many cases the dielectric strength of a material will be the determining factor in the design of the apparatus in which it is to be used.  
5.2 Tests made as specified herein are suitable for use to provide part of the information needed for determining suitability of a material for a given application; and also, for detecting changes or deviations from normal characteristics resulting from processing variables, aging conditions, or other manufacturing or environmental situations. This test method is useful for process control, acceptance or research testing.  
5.3 Results obtained by this test method can seldom be used directly to determine the dielectric behavior of a material in an actual application. In most cases it is necessary that these results be evaluated by comparison with results obtained from other functional tests or from tests on other materials, or both, in order to estimate their significance for a particular material.  
5.4 Three methods for voltage application are specified in Section 12: Method A, Short-Time Test; Method B, Step-by-Step Test; and Method C, Slow Rate-of-Rise Test. Method A is the most commonly-used test for quality-control tests. However, the longer-time tests, Methods B and C, which usually will give lower test results, will potentially give more meaningful results when different materials are being compared with each other. If a test set with motor-driven voltage control is available, the slow rate-of-rise test is simpler and preferable to the step-by-step test. The results obtained from Methods B and C are comparable to each other.  
5.5 Documents specifying the use of this test method shall also specify:  
5.5.1 Method of voltage application,  
5.5.2 Voltage rate-of-rise, if slow rate-of-rise method is specified,  
5.5.3 Specimen selection, preparation, and conditio...
SCOPE
1.1 This test method covers procedures for the determination of dielectric strength of solid insulating materials at commercial power frequencies, under specified conditions.2,3  
1.2 Unless otherwise specified, the tests shall be made at 60 Hz. However, this test method is suitable for use at any frequency from 25 to 800 Hz. At frequencies above 800 Hz, dielectric heating is a potential problem.  
1.3 This test method is intended to be used in conjunction with any ASTM standard or other document that refers to this test method. References to this document need to specify the particular options to be used (see 5.5).  
1.4 It is suitable for use at various temperatures, and in any suitable gaseous or liquid surrounding medium.  
1.5 This test method is not intended for measuring the dielectric strength of materials that are fluid under the conditions of test.  
1.6 This test method is not intended for use in determining intrinsic dielectric strength, direct-voltage dielectric strength, or thermal failure under electrical stress (see Test Method D3151).  
1.7 This test method is most commonly used to determine the dielectric breakdown voltage through the thickness of a test specimen (puncture). It is also suitable for use to determine dielectric breakdown voltage along the interface between a solid specimen and a gaseous or liquid surrounding medium (flashover). With the addition of instructions modifying Section 12, this test method is also suitable for use for proof testing.  
1.8 This test method is similar to IEC Publication 243-1. All procedures in this method are included in IEC 243-1. Differences between this method and IEC 243-1 are largely editorial.  
1.9 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 determine the applicabil...

General Information

• Status: Published
• Publication Date: 31-Dec-2019
• ICS: 29.035.01 - Insulating materials in general
• Technical Committee: D09 - Electrical and Electronic Insulating Materials
• Drafting Committee: D09.12 - Electrical Tests

Relations

• Replaces: ASTM D149-09(2013) - Standard Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials at Commercial Power Frequencies
• Effective Date: 01-Jan-2020
• Refers: ASTM D1711-24 - Standard Terminology Relating to Electrical Insulation
• Effective Date: 01-Mar-2024
• Refers: ASTM D3487-16 - Standard Specification for Mineral Insulating Oil Used in Electrical Apparatus
• Effective Date: 15-Jun-2016
• Refers: ASTM D3487-16e1 - Standard Specification for Mineral Insulating Oil Used in Electrical Apparatus
• Effective Date: 15-Jun-2016
• Refers: ASTM D1711-15 - Standard Terminology Relating to Electrical Insulation
• Effective Date: 01-Nov-2015
• Refers: ASTM D1711-14a - Standard Terminology Relating to Electrical Insulation
• Effective Date: 01-Nov-2014
• Refers: ASTM D1711-14 - Standard Terminology Relating to Electrical Insulation
• Effective Date: 01-May-2014
• Refers: ASTM D1711-13 - Standard Terminology Relating to Electrical Insulation
• Effective Date: 01-Nov-2013
• Refers: ASTM D1711-11a - Standard Terminology Relating to Electrical Insulation
• Effective Date: 01-Aug-2011
• Refers: ASTM D3487-09 - Standard Specification for Mineral Insulating Oil Used in Electrical Apparatus
• Effective Date: 01-Dec-2009
• Refers: ASTM D2413-99(2009) - Standard Practice for Preparation of Insulating Paper and Board Impregnated with a Liquid Dielectric
• Effective Date: 01-Oct-2009
• Refers: ASTM D618-08 - Standard Practice for Conditioning Plastics for Testing
• Effective Date: 01-Nov-2008
• Refers: ASTM D3487-08 - Standard Specification for Mineral Insulating Oil Used in Electrical Apparatus
• Effective Date: 01-Nov-2008
• Refers: ASTM D1711-08 - Standard Terminology Relating to Electrical Insulation
• Effective Date: 01-May-2008
• Refers: ASTM D877-02(2007) - Standard Test Method for Dielectric Breakdown Voltage of Insulating Liquids Using Disk Electrodes
• Effective Date: 01-Oct-2007

Overview

ASTM D149-20 is a critical standard developed by ASTM International detailing the Standard Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials at Commercial Power Frequencies. This document outlines procedures to determine the dielectric strength and breakdown voltage of solid insulating materials used in electrical applications operating at power frequencies, typically 60 Hz, but suitable for frequencies ranging from 25 to 800 Hz.

These tests provide essential data to evaluate the suitability of insulating materials in environments exposed to electrical fields. ASTM D149-20 supports material selection, quality control, process optimization, and research in industries such as electrical equipment manufacturing, electronics, and energy.

Key Topics

• Dielectric Breakdown Voltage: The minimum voltage at which a material loses its insulating property and allows current to pass through.
• Dielectric Strength: The maximum electric field a material can withstand without experiencing dielectric failure.
• Voltage Application Methods: Three standardized procedures are specified for voltage application during testing:
  • Short-Time Test (Method A): Rapid voltage increase; commonly used for quality control.
  • Step-by-Step Test (Method B): Incremental voltage steps; useful for comparing different materials.
  • Slow Rate-of-Rise Test (Method C): Gradual voltage increase; especially suitable when comparing materials using motor-driven voltage sources.
• Test Conditions: The standard emphasizes the importance of specifying test parameters such as frequency, voltage application method, specimen preparation, surrounding medium (air, oil, or gas), temperature, and electrode configuration.
• Scope Limitations: ASTM D149-20 does not address intrinsic dielectric strength, direct-voltage dielectric strength, or thermal failures under electrical stress.

Applications

ASTM D149-20 is widely implemented across industries where high electrical insulation reliability is crucial, including:

• Material Qualification: Assessing if solid electrical insulating materials such as polymers, papers, rubbers, ceramics, and glass meet safety and performance requirements for use in transformers, motors, cables, and other electrical apparatus.
• Process Control and Quality Assurance: Monitoring production batches for consistency and detecting deviations due to aging or manufacturing changes.
• Research and Development: Comparing materials under standardized conditions to evaluate performance innovations or effects of environmental exposure and process modifications.
• Acceptance Testing: Establishing product conformity prior to shipment or installation, ensuring claimed dielectric strength is achieved.

The method is versatile-it allows testing at various temperatures and in different insulating environments to simulate real operating conditions. It is not intended for materials that are fluid under test conditions or applications specifically requiring direct-current or intrinsic dielectric strength measurements.

Related Standards

• ASTM D374: Test Methods for Thickness of Solid Electrical Insulation.
• ASTM D618: Practice for Conditioning Plastics for Testing.
• ASTM D877: Test Method for Dielectric Breakdown Voltage of Insulating Liquids.
• ASTM D1711: Terminology Relating to Electrical Insulation.
• ASTM D2413: Practice for Preparation of Insulating Paper and Board Impregnated with a Liquid Dielectric.
• ASTM D3151: Test Method for Thermal Failure of Solid Electrical Insulating Materials Under Electric Stress.
• IEC 243-1: Methods of Test for Electrical Strength of Solid Insulating Materials at Power Frequencies.
• ANSI C68.1 / IEEE Standard 4: Techniques for Dielectric Tests.

By adhering to ASTM D149-20, professionals ensure accurate, repeatable measurement of dielectric strength, enabling better design and greater reliability in electrical systems. For more comprehensive information, users should consult the full text of the standard and related documents listed above.

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: D149 − 20
Standard Test Method for
Dielectric Breakdown Voltage and Dielectric Strength of
Solid Electrical Insulating Materials at Commercial Power
Frequencies
This standard is issued under the fixed designation D149; 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 (´) 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* (flashover). With the addition of instructions modifying Sec-
tion 12, this test method is also suitable for use for proof
1.1 This test method covers procedures for the determina-
testing.
tion of dielectric strength of solid insulating materials at
2,3
commercial power frequencies, under specified conditions. 1.8 ThistestmethodissimilartoIECPublication243-1.All
procedures in this method are included in IEC 243-1. Differ-
1.2 Unless otherwise specified, the tests shall be made at 60
encesbetweenthismethodandIEC243-1arelargelyeditorial.
Hz. However, this test method is suitable for use at any
1.9 This standard does not purport to address all of the
frequency from 25 to 800 Hz. At frequencies above 800 Hz,
safety concerns, if any, associated with its use. It is the
dielectric heating is a potential problem.
responsibility of the user of this standard to establish appro-
1.3 This test method is intended to be used in conjunction
priate safety, health, and environmental practices and deter-
with anyASTM standard or other document that refers to this
mine the applicability of regulatory limitations prior to use.
test method. References to this document need to specify the
Specific hazard statements are given in Section 7. See also
particular options to be used (see 5.5).
6.4.1.
1.4 It is suitable for use at various temperatures, and in any
1.10 This international standard was developed in accor-
suitable gaseous or liquid surrounding medium.
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
1.5 This test method is not intended for measuring the
Development of International Standards, Guides and Recom-
dielectric strength of materials that are fluid under the condi-
mendations issued by the World Trade Organization Technical
tions of test.
Barriers to Trade (TBT) Committee.
1.6 This test method is not intended for use in determining
intrinsic dielectric strength, direct-voltage dielectric strength,
2. Referenced Documents
or thermal failure under electrical stress (see Test Method
2.1 ASTM Standards:
D3151).
D374Test Methods for Thickness of Solid Electrical Insu-
1.7 This test method is most commonly used to determine
lation (Metric) D0374_D0374M
thedielectricbreakdownvoltagethroughthethicknessofatest
D618Practice for Conditioning Plastics for Testing
specimen (puncture). It is also suitable for use to determine
D877Test Method for Dielectric Breakdown Voltage of
dielectric breakdown voltage along the interface between a
Insulating Liquids Using Disk Electrodes
solid specimen and a gaseous or liquid surrounding medium
D1711Terminology Relating to Electrical Insulation
D2413Practice for Preparation of Insulating Paper and
Board Impregnated with a Liquid Dielectric
This test method is under the jurisdiction of ASTM Committee D09 on
Electrical and Electronic Insulating Materials and is the direct responsibility of
D3151Test Method for Thermal Failure of Solid Electrical
Subcommittee D09.12 on Electrical Tests.
Insulating Materials Under Electric Stress (Withdrawn
Current edition approved Jan. 1, 2020. Published January 2020. Originally
2007)
approved in 1922. Last previous edition approved in 2013 as D149–09(2013).
DOI: 10.1520/D0149-20.
Bartnikas, R., Chapter 3, “High Voltage Measurements,” Electrical Properties
of Solid Insulating Materials, Measurement Techniques, Vol. IIB, Engineering For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Dielectrics, R. Bartnikas, Editor, ASTM STP 926, ASTM, Philadelphia, 1987. contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Nelson, J. K., Chapter 5, “Dielectric Breakdown of Solids,” Electrical Standards volume information, refer to the standard’s Document Summary page on
Properties of Solid Insulating Materials: Molecular Structure and Electrical the ASTM website.
Behavior, Vol. IIA, Engineering Dielectrics, R. Bartnikas and R. M. Eichorn, The last approved version of this historical standard is referenced on
Editors, ASTM STP 783, ASTM, Philadelphia, 1983. www.astm.org.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D149 − 20
D3487Specification for Mineral Insulating Oil Used in electrical field will be present. In many cases the dielectric
Electrical Apparatus strength of a material will be the determining factor in the
D5423Specification for Forced-Convection Laboratory Ov- design of the apparatus in which it is to be used.
ens for Evaluation of Electrical Insulation
5.2 Tests made as specified herein are suitable for use to
2.2 IEC Standard:
provide part of the information needed for determining suit-
Pub. 243-1Methods of Test for Electrical Strength of Solid
ability of a material for a given application; and also, for
Insulating Materials—Part 1:Tests at Power Frequencies
detecting changes or deviations from normal characteristics
2.3 ANSI Standard:
resulting from processing variables, aging conditions, or other
C68.1 Techniques for Dielectric Tests, IEEE Standard No.
manufacturing or environmental situations.This test method is
useful for process control, acceptance or research testing.
3. Terminology
5.3 Resultsobtainedbythistestmethodcanseldombeused
directly to determine the dielectric behavior of a material in an
3.1 Definitions:
actual application. In most cases it is necessary that these
3.1.1 dielectric breakdown voltage (electric breakdown
results be evaluated by comparison with results obtained from
voltage), n—the potential difference at which dielectric failure
other functional tests or from tests on other materials, or both,
occurs under prescribed conditions in an electrical insulating
in order to estimate their significance for a particular material.
material located between two electrodes. (See also Appendix
X1.)
5.4 Three methods for voltage application are specified in
3.1.1.1 Discussion—The term dielectric breakdown voltage
Section 12: Method A, Short-Time Test; Method B, Step-by-
is sometimes shortened to “breakdown voltage.”
StepTest; and Method C, Slow Rate-of-RiseTest. MethodAis
the most commonly-used test for quality-control tests.
3.1.2 dielectric failure (under test), n—an event that is
However, the longer-time tests, Methods B and C, which
evidencedbyanincreaseinconductanceinthedielectricunder
usually will give lower test results, will potentially give more
test limiting the electric field that can be sustained.
meaningful results when different materials are being com-
3.1.3 dielectric strength, n—the voltage gradient at which
pared with each other. If a test set with motor-driven voltage
dielectric failure of the insulating material occurs under spe-
control is available, the slow rate-of-rise test is simpler and
cific conditions of test.
preferable to the step-by-step test. The results obtained from
3.1.4 electric strength, n—see dielectric strength.
Methods B and C are comparable to each other.
3.1.4.1 Discussion—Internationally, “electric strength” is
5.5 Documents specifying the use of this test method shall
used almost universally.
also specify:
3.1.5 flashover (as related to electrical), n—an electrical
5.5.1 Method of voltage application,
discharge between two electrodes which occurs around the
5.5.2 Voltage rate-of-rise, if slow rate-of-rise method is
surface of a solid dielectric in the surrounding medium.
specified,
3.1.6 For definitions of other terms relating to solid insulat-
5.5.3 Specimen selection, preparation, and conditioning,
ing materials, refer to Terminology D1711.
5.5.4 Surrounding medium and temperature during test,
5.5.5 Electrodes,
4. Summary of Test Method
5.5.6 Wherever possible, the failure criterion of the current-
4.1 Alternating voltage at a commercial power frequency
sensing element, and
(60 Hz, unless otherwise specified) is applied to a test
5.5.7 Any desired deviations from the recommended proce-
specimen. The voltage is increased from zero or from a level
dures as given.
well below the breakdown voltage, in one of three prescribed
5.6 If any of the requirements listed in 5.5 are missing from
methods of voltage application, until dielectric failure of the
the specifying document, then the recommendations for the
test specimen occurs.
several variables shall be followed.
4.2 Mostcommonly,thetestvoltageisappliedusingsimple
5.7 Unless the items listed in 5.5 are specified, tests made
test electrodes on opposite faces of specimens.The options for
with such inadequate reference to this test method are not in
the specimens are that they be molded or cast, or cut from flat
conformancewiththistestmethod.Iftheitemslistedin5.5are
sheetorplate.Otherelectrodeandspecimenconfigurationsare
not closely controlled during the test, it is possible that the
also suitable for use to accommodate the geometry of the
precisions stated in 15.2 and 15.3 will not be obtained.
samplematerial,ortosimulateaspecificapplicationforwhich
5.8 Variations in the failure criteria (current setting and
the material is being evaluated.
response time) of the current sensing element significantly
5. Significance and Use
affect the test results.
5.1 The dielectric strength of an electrical insulating mate-
5.9 Appendix X1 contains a more complete discussion of
rial is a property of interest for any application where an
the significance of dielectric strength tests.
Available from International Electrotechnical Commission (IEC), 3 rue de 6. Apparatus
Varembé, Case postale 131, CH-1211, Geneva 20, Switzerland, http://www.iec.ch.
6.1 Voltage Source—Obtain the test voltage from a step-up
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. transformer supplied from a variable sinusoidal low-voltage
D149 − 20
source. The transformer, its voltage source, and the associated 6.1.5 It is important for the circuit-breaking device to have
controls shall have the following capabilities: an adjustable current-sensing element in the step-up trans-
6.1.1 The ratio of crest to root-mean-square (rms) test former secondary, to allow for adjustment consistent with the
specimen characteristics and arranged to sense specimen cur-
voltage shall be equal to =265% 1.34 to1.48 , with the test
~ !
rent. Set the sensing element to respond to a current that is
specimen in the circuit, at all voltages greater than 50% of the
indicative of specimen breakdown as defined in 12.3.
breakdown voltage.
6.1.6 Thecurrentsettingislikelytohaveasignificanteffect
6.1.2 The capacity of the source shall be sufficient to
onthetestresults.Makethesettinghighenoughthattransients,
maintainthetestvoltageuntildielectricbreakdownoccurs.For
such as partial discharges, will not trip the breaker but not so
most materials, using electrodes similar to those shown in
high that excessive burning of the specimen, with resultant
Table 1, an output current capacity of 40 mA is usually
electrode damage, will occur on breakdown. The optimum
satisfactory. For more complex electrode structures, or for
currentsettingisnotthesameforallspecimensanddepending
testing high-loss materials, it is possible that higher current
upon the intended use of the material and the purpose of the
capacity will be needed. The power rating for most tests will
test, it is often desirable to make tests on a given sample at
vary from 0.5 kVA for testing low-capacitance specimens at
more than one current setting. The electrode area is likely to
voltages up to 10 kV, to 5 kVA for voltages up to 100 kV.
have a significant effect upon the choice of current setting.
6.1.3 The controls on the variable low-voltage source shall
6.1.7 It is possible that the specimen current-sensing ele-
be capable of varying the supply voltage and the resultant test
ment will be in the primary of the step-up transformer.
voltage smoothly, uniformly, and without overshoots or
Calibratethecurrent-sensingdialintermsofspecimencurrent.
transients, in accordance with 12.2. Do not allow the peak
6.1.8 Exercise care in setting the response of the current
voltage to exceed 1.48 times the indicated rms test voltage
control. If the control is set too high, the circuit will not
under any circumstance. Motor-driven controls are preferable
respond when breakdown occurs; if set too low, it is possible
for making short-time (see 12.2.1) or slow-rate-of-rise (see
that it will respond to leakage currents, capacitive currents, or
12.2.3) tests.
partial discharge (corona) currents or, when the sensing ele-
6.1.4 Equip the voltage source with a circuit-breaking
ment is located in the primary, to the step-up transformer
device that will operate within three cycles. The device shall
magnetizing current.
disconnect the voltage-source equipment from the power
6.2 Voltage Measurement—A voltmeter must be provided
service and protect it from overload as a result of specimen
for measuring the rms test voltage. If a peak-reading voltmeter
breakdown causing an overload of the testing apparatus. If
prolonged current follows breakdown it will result in unnec- is used, divide the reading by =2 to get rms values. The
essary burning of the test specimens, pitting of the electrodes, overall error of the voltage-measuring circuit shall not exceed
and contamination of any liquid surrounding medium. 5% of the measured value. In addition, the response time of
A
TABLE 1 Typical Electrodes for Dielectric Strength Testing of Various Types of Insulating Materials
Electrode
B,C
Description of Electrodes Insulating Materials
Type
1 Opposing cylinders 51 mm (2 in.) in diameter, 25 mm (1 in.) thick with flat sheets of paper, films, fabrics, rubber, molded plastics, laminates,
edges rounded to 6.4 mm (0.25 in.) radius boards, glass, mica, and ceramic
2 Opposing cylinders 25 mm (1 in.) in diameter, 25 mm (1 in.) thick with same as for Type 1, particularly for glass, mica, plastic, and ceramic
edges rounded to 3.2 mm (0.125 in.) radius
3 Opposing cylindrical rods 6.4 mm (0.25 in.) in diameter with edges same as for Type 1, particularly for varnish, plastic, and other thin film and
D
rounded to 0.8 mm (0.0313 in.) radius tapes: where small specimens necessitate the use of smaller electrodes,
or where testing of a small area is desired
4 Flat plates 6.4 mm (0.25 in.) wide and 108 mm (4.25 in.) long with edges same as for Type 1, particularly for rubber tapes and other narrow widths
square and ends rounded to 3.2 mm (0.125 in.) radius of thin materials
E
5 Hemispherical electrodes 12.7 mm (0.5 in.) in diameter filling and treating compounds, gels and semisolid compounds and greases,
embedding, potting, and encapsulating materials
6 Opposing cylinders; the lower one 75 mm (3 in.) in diameter, 15 mm same as for Types 1 and 2
(0.60 in.) thick; the upper one 25 mm (1 in.) in diameter, 25 mm
F
thick; with edges of both rounded to 3 mm (0.12 in.) radius
G
7 Opposing circular flat plates, 150 mm diameter , 10 mm thick with flat sheet, plate, or board materials, for tests with the voltage gradient
H
edges rounded to 3 to 5 mm radius
parallel to the surface
A
These electrodes are those most commonly specified or referenced inASTM standards. With the exception ofType 5 electrodes, no attempt has been made tosuggest
electrode systems for other than flat surface material. It is acceptable to use other electrodes as specified in ASTM standards or as agreed upon between seller and
purchaser where none of these electrodes in the table is suitable for proper evaluation of the material being tested.
B
Electrodes are normally made from either brass or stainless steel. Reference shall be made to the standard governing the material to be tested to determine which, if
either, material is preferable.
C
The electrodes surfaces shall be polished and free from irregularities resulting from previous testing.
D
Refer to the appropriate standard for the load force applied by the upper electrode assembly. Unless otherwise specified the upper electrodes shall be50±2g.
E
Refer to the appropriate standard for the proper gap settings.
F
TheType 6 electrodes are those given in IEC Publication 243-1 for testing of flat sheet materials.They are less critical as to concentricity of the electrodes than are the
Types 1 and 2 electrodes.
G
It is acceptable to use other diameters, provided that all parts of the test specimen are at least 15 mm inside the edges of the electrodes.
H G
The Type 7 electrodes, as described in the table and in Note , are those given in IEC Publication 243-1 for making tests parallel to the surface.
D149 − 20
the voltmeter shall be such that its time lag will not be greater 6.3.7 In some special cases liquid metal electrodes, foil
than 1% of full scale at any rate-of-rise used. electrodes, metal shot, water, or conductive coating electrodes
areused.Itmustberecognizedthatitispossiblethatthesewill
6.2.1 Measure the voltage using a voltmeter or potential
give results differing widely from those obtained with other
transformer connected to the specimen electrodes, or to a
types of electrodes.
separate voltmeter winding, on the test transformer, that is
6.3.8 Because of the effect of the electrodes on the test
unaffected by the step-up transformer loading.
results, it is frequently possible to obtain additional informa-
6.2.2 It is desirable for the reading of the maximum applied
tion as to the dielectric properties of a material (or a group of
test voltage to be retained on the voltmeter after breakdown so materials) by running tests with more than one type of
that the breakdown voltage can be accurately read and re- electrode. This technique is of particular value for research
testing.
corded.
6.4 Surrounding Medium—The document calling for this
6.3 Electrodes—For a given specimen configuration, it is
test method needs to specify the surrounding medium and the
possible that the dielectric breakdown voltage will vary
test temperature. Since flashover must be avoided and the
considerably, depending upon the geometry and placement of
effects of partial discharges prior to breakdown mimimized,
the test electrodes. For this reason it is important that the
even for short time tests, it is often preferable and sometimes
electrodes to be used be described when specifying this test
necessary to make the tests in insulating liquid (see 6.4.1).
method, and that they be described in the report.
Breakdown values obtained in insulating liquid are often not
6.3.1 One of the electrodes listed in Table 1 shall be
comparable with those obtained in air. The nature of the
specified by the document referring to this test method. If no
insulating liquid and the degree of previous use are factors
electrodes have been specified, select an applicable one from
influencing the test values. In some cases, testing in air will
Table 1, or use other electrodes mutually acceptable to the
require excessively large specimens or cause heavy surface
parties concerned when the standard electrodes cannot be used
discharges and burning before breakdown. Some electrode
due to the nature or configuration of the material being tested. systems for testing in air make use of pressure gaskets around
See references in Appendix X2 for examples of some special the electrodes to prevent flashover.The material of the gaskets
or seals around the electrodes has the potential to influence the
electrodes.Inanyeventtheelectrodesmustbedescribedinthe
breakdown values.
report.
6.4.1 When tests are made in insulating oil, an oil bath of
6.3.2 The electrodes of Types 1 through 4 and Type 6 of
adequate size shall be provided. (Warning—The use of glass
Table 1 shall be in contact with the test specimen over the
containers is not recommended for tests at voltages above
entire flat area of the electrodes.
about10kV,becausetheenergyreleasedatbreakdownhasthe
6.3.3 The specimens tested usingType 7 electrodes shall be
potential to be sufficient to shatter the container. Metal baths
ofsuchsizethatallportionsofthespecimenwillbewithinand
must be grounded.)
no less than 15 mm from the edges of the electrodes during
Itisrecommendedthatmineraloilmeetingtherequirements
test.Inmostcases,testsusingType7electrodesaremadewith
of Specification D3487, Type I or II, be used. It shall have a
the plane of the electrode surfaces in a vertical position. Tests
dielectric breakdown voltage as determined by Test Method
madewithhorizontalelectrodesshallnotbedirectlycompared
D877 of at least 26 kV. Other dielectric fluids are suitable for
with tests made with vertical electrodes, particularly when the
useassurroundingmediumsifspecified.Theseinclude,butare
tests are made in a liquid surrounding medium.
notlimitedto,siliconefluidsandotherliquidsintendedforuse
in transformers, circuit breakers, capacitors, or cables.
6.3.4 Keep the electrode surfaces clean and smooth, and
6.4.1.1 The quality of the insulating oil has the potential to
freefromprojectingirregularitiesresultingfromprevioustests.
have an appreciable effect upon the test results. In addition to
If asperities have developed, they must be removed.
thedielectricbreakdownvoltage,mentionedabove,particulate
6.3.5 It is important that the original manufacture and
contaminants are especially important when very thin speci-
subsequent resurfacing of electrodes be done in such a manner
mens (25 µm (1 mil) or less) are being tested. Depending upon
that the specified shape and finish of the electrodes and their
the nature of the oil and the properties of the material being
edges are maintained. The flatness and surface finish of the
tested, other properties, including dissolved gas content, water
electrode faces must be such that the faces are in close contact
content,anddissipationfactoroftheoilalsohavethepotential
with the test specimen over the entire area of the electrodes.
to affect the results. Frequent replacement of the oil, or the use
Surface finish is particularly important when testing very thin
of filters and other reconditioning equipment is important to
materials which are subject to physical damage from improp-
minimizetheeffectofvariationsofthequalityoftheoilonthe
erly finished electrodes. When resurfacing, do not change the
test results.
transition between the electrode face and any specified edge
6.4.1.2 Breakdown values obtained using liquids having
radius.
different electrical properties are often not comparable. (See
6.3.6 Whenever the electrodes are dissimilar in size or
X1.4.7.)Iftestsaretobemadeatotherthanroomtemperature,
shape, ensure that the one at which the lowest concentration of
the bath must be provided with a means for heating or cooling
stress exists, usually the larger in size and with the largest
the liquid, and with a means to ensure uniform temperature.
radius, is at ground potential. Small baths can in some cases be placed in an oven (see 6.4.2)
D149 − 20
inordertoprovidetemperaturecontrol.Ifforcedcirculationof 7.2 Warning—Ozone is a physiologically hazardous gas at
the fluid is provided, care must be taken to prevent bubbles elevated concentrations. The exposure limits are set by gov-
from being whipped into the fluid. The temperature shall be ernmental agencies and are usually based upon recommenda-
maintainedwithin 65°Cofthespecifiedtesttemperatureatthe tions made by the American Conference of Governmental
Industrial Hygienists. Ozone is likely to be present whenever
electrodes, unless otherwise specified. In many cases it is
specified that specimens to be tested in insulating oil are to be voltagesexistwhicharesufficienttocausepartial,orcomplete,
discharges in air or other atmospheres that contain oxygen.
previously impregnated with the oil and not removed from the
oil before testing (see Practice D2413). For such materials, the Ozone has a distinctive odor which is initially discernible at
lowconcentrationsbutsustainedinhalationofozonecancause
bath must be of such design that it will not be necessary to
temporary loss of sensitivity to the scent of ozone. Because of
expose the specimens to air before testing.
thisitisimportanttomeasuretheconcentrationofozoneinthe
6.4.2 If tests in air are to be made at other than ambient
atmosphere, using commercially available monitoring devices,
temperature or humidity, an oven or controlled humidity
whenever the odor of ozone is persistently present or when
chamber must be provided for the tests. Ovens meeting the
ozone generating conditions continue. Use appropriate means,
requirements of Specification D5423 and provided with means
such as exhaust vents, to reduce ozone concentrations to
for introducing the test voltage will be suitable for use when
acceptable levels in working areas.
only temperature is to be controlled.
6.4.3 Testsingassesotherthanairwillgenerallyrequirethe
8. Sampling
use of chambers that can be evacuated and filled with the test
8.1 The detailed sampling procedure for the material being
gas, usually under some controlled pressure. The design of
tested needs to be defined in the specification for that material.
such chambers will be determined by the nature of the test
program to be undertaken.
8.2 Sampling procedures for quality control purposes shall
provide for gathering of sufficient samples to estimate both the
6.5 Test Chamber—The test chamber or area in which the
average quality and the variability of the lot being examined;
tests are to be made shall be of sufficient size to hold the test
andforproperprotectionofthesamplesfromthetimetheyare
equipment, and shall be provided with interlocks to prevent
taken until the preparation of the test specimens in the
accidental contact with any electrically energized parts. A
laboratory or other test area is begun.
number of different physical arrangements of voltage source,
measuring equipment, baths or ovens, and electrodes are 8.3 For the purposes of most tests it is desirable to take
possible, but it is essential that (1) all gates or doors providing samples from areas that are not immediately adjacent to
access to spaces in which there are electrically energized parts obvious defects or discontinuities in the material. Avoid the
be interlocked to shut off the voltage source when opened; (2) outer few layers of roll material, the top sheets of a package of
clearances are sufficiently large that the field in the area of the sheets, or material immediately next to an edge of a sheet or
electrodes and specimen are not distorted and that flashovers roll, unless the presence or proximity of defects or disconti-
nuities is of interest in the investigation of the material.
and partial discharges (corona) do not occur except between
the test electrodes; and (3) insertion and replacement of
8.4 The sample shall be large enough to permit making as
specimens between tests be as simple and convenient as
many individual tests as required for the particular material
possible.Visualobservationoftheelectrodesandtestspecimen
(see 12.4).
during the test is frequently desirable.
9. Test Specimens
7. Hazards
9.1 Preparation and Handling:
7.1 Warning—It is possible that lethal voltages will be
9.1.1 Prepare specimens from samples collected in accor-
present during this test. It is essential that the test apparatus,
dance with Section 8.
and all associated equipment electrically connected to it, be
9.1.2 Whenflat-facedelectrodesaretobeused,thesurfaces
properly designed and installed for safe operation. Solidly
of the specimens which will be in contact with the electrodes
ground all electrically conductive parts that any person might
shall be smooth parallel planes, insofar as possible without
come into contact with during the test. Provide means for use
actual surface machining.
atthecompletionofanytesttogroundanypartswhichfallinto
9.1.3 The specimens shall be of sufficient size to prevent
any of the following cases: (a) were at high voltage during the
flashover under the conditions of test. For thin materials it will
test; (b) have the potential to acquire an induced charge during often be convenient to use specimens large enough to permit
the test; or (c) have the potential to retain a charge even after
making more than one test on a single piece.
disconnection of the voltage source. Thoroughly instruct all 9.1.4 For thicker materials (usually more than 2 mm thick)
operators in the proper way to conduct tests safely. When
it is possible that the breakdown strength will be high enough
makinghigh-voltagetests,particularlyincompressedgasorin thatflashoverorintensesurfacepartialdischarges(corona)will
oil, it is possible that the energy released at breakdown will be
sufficient to result in fire, explosion, or rupture of the test
chamber. Design test equipment, test chambers, and test
Available from American Conference of Governmental Industrial Hygienists,
specimens so as to minimize the possibility of such occur-
Inc. (ACGIH), 1330 Kemper Meadow Dr., Cincinnati, OH 45240, http://
rences and to eliminate the possibility of personal injury. www.acgih.org.
D149 − 20
occur prior to breakdown. Techniques that are suitable for use 11.2 Unless otherwise specified, follow the procedures in
to prevent flashover, or to reduce partial discharge (corona) Practice D618.
include:
11.3 For many materials the moisture content has more
9.1.4.1 Immerse the specimen in insulating oil during the
effect on dielectric strength than does temperature. Condition-
test. See X1.4.7 for the surrounding medium factors influenc-
ingtimesforthesematerialsshallbesufficientlylongtopermit
ingbreakdown.Thisisoftennecessaryforspecimensthathave
the specimens to reach moisture equilibrium as well as
not been dried and impregnated with oil, as well as for those
temperature equilibrium.
which have been prepared in accordance with Practice D2413,
11.4 If the conditioning atmosphere is such that condensa-
for example. (See 6.4.)
tionoccursonthesurfaceofthespecimens,itisoftendesirable
9.1.4.2 Machinearecessordrillaflat-bottomholeinoneor
to wipe the surfaces of the specimens immediately before
both surfaces of the specimen to reduce the test thickness. If
testing. This will usually reduce the probability of surface
dissimilar electrodes are used (such as Type 6 of Table 1) and
flashover.
only one surface is to be machined, the larger of the two
electrodes shall be in contact with the machined surface. Care
12. Procedure
must be taken in machining specimens not to contaminate or
12.1 (Warning—see Section 7 before commencement of
mechanically damage them.
any test.)
9.1.4.3 Apply seals or shrouds around the electrodes, in
12.2 Methods of Voltage Application:
contact with the specimen to reduce the tendency to flashover.
12.2.1 Method A, Short-Time Test—Apply voltage uni-
9.1.5 Materials that are not in flat sheet form shall be tested
formlytothetestelectrodesfromzeroatoneoftheratesshown
using specimens (and electrodes) appropriate to the material
inFig.1untilbreakdownoccurs.Usetheshort-timetestunless
and the geometry of the sample. It is essential that for these
otherwise specified.
materials both the specimen and the electrodes b
...

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: D149 − 09 (Reapproved 2013) D149 − 20
Standard Test Method for
Dielectric Breakdown Voltage and Dielectric Strength of
Solid Electrical Insulating Materials at Commercial Power
Frequencies
This standard is issued under the fixed designation D149; 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 covers procedures for the determination of dielectric strength of solid insulating materials at commercial
2,3
power frequencies, under specified conditions.
1.2 Unless otherwise specified, the tests shall be made at 60 Hz. However, this test method is suitable for use at any frequency
from 25 to 800 Hz. At frequencies above 800 Hz, dielectric heating is a potential problem.
1.3 This test method is intended to be used in conjunction with any ASTM standard or other document that refers to this test
method. References to this document need to specify the particular options to be used (see 5.5).
1.4 It is suitable for use at various temperatures, and in any suitable gaseous or liquid surrounding medium.
1.5 This test method is not intended for measuring the dielectric strength of materials that are fluid under the conditions of test.
1.6 This test method is not intended for use in determining intrinsic dielectric strength, direct-voltage dielectric strength, or
thermal failure under electrical stress (see Test Method D3151).
1.7 This test method is most commonly used to determine the dielectric breakdown voltage through the thickness of a test
specimen (puncture). It is also suitable for use to determine dielectric breakdown voltage along the interface between a solid
specimen and a gaseous or liquid surrounding medium (flashover). With the addition of instructions modifying Section 12, this test
method is also suitable for use for proof testing.
1.8 This test method is similar to IEC Publication 243-1. All procedures in this method are included in IEC 243-1. Differences
between this method and IEC 243-1 are largely editorial.
1.9 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use. Specific hazard statements are given in Section 7. Also seeSee also 6.4.1.
1.10 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:
D374 Test Methods for Thickness of Solid Electrical Insulation (Metric) D0374_D0374M
D618 Practice for Conditioning Plastics for Testing
This test method is under the jurisdiction of ASTM Committee D09 on Electrical and Electronic Insulating Materials and is the direct responsibility of Subcommittee
D09.12 on Electrical Tests.
Current edition approved April 1, 2013Jan. 1, 2020. Published April 2013January 2020. Originally approved in 1922. Last previous edition approved in 20092013 as
D149 – 09.D149 – 09 (2013). DOI: 10.1520/D0149-09R13.10.1520/D0149-20.
Bartnikas, R., Chapter 3, “High Voltage Measurements,” Electrical Properties of Solid Insulating Materials, Measurement Techniques, Vol. IIB, Engineering Dielectrics,
R. Bartnikas, Editor, ASTM STP 926, ASTM, Philadelphia, 1987.
Nelson, J. K., Chapter 5, “Dielectric Breakdown of Solids,” Electrical Properties of Solid Insulating Materials: Molecular Structure and Electrical Behavior, Vol. IIA,
Engineering Dielectrics, R. Bartnikas and R. M. Eichorn, Editors, ASTM STP 783, ASTM, Philadelphia, 1983.
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.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D149 − 20
D877 Test Method for Dielectric Breakdown Voltage of Insulating Liquids Using Disk Electrodes
D1711 Terminology Relating to Electrical Insulation
D2413 Practice for Preparation of Insulating Paper and Board Impregnated with a Liquid Dielectric
D3151 Test Method for Thermal Failure of Solid Electrical Insulating Materials Under Electric Stress (Withdrawn 2007)
D3487 Specification for Mineral Insulating Oil Used in Electrical Apparatus
D5423 Specification for Forced-Convection Laboratory Ovens for Evaluation of Electrical Insulation
2.2 IEC Standard:
Pub. 243-1 Methods of Test for Electrical Strength of Solid Insulating Materials—Part 1: Tests at Power Frequencies
2.3 ANSI Standard:
C68.1 Techniques for Dielectric Tests, IEEE Standard No. 4
3. Terminology
3.1 Definitions:
3.1.1 dielectric breakdown voltage (electric breakdown voltage), n—the potential difference at which dielectric failure occurs
under prescribed conditions in an electrical insulating material located between two electrodes. (See also Appendix X1.)
3.1.1.1 Discussion—
The term dielectric breakdown voltage is sometimes shortened to “breakdown voltage.”
3.1.2 dielectric failure (under test), n—an event that is evidenced by an increase in conductance in the dielectric under test
limiting the electric field that can be sustained.
3.1.3 dielectric strength, n—the voltage gradient at which dielectric failure of the insulating material occurs under specific
conditions of test.
3.1.4 electric strength, n—see dielectric strength.
3.1.4.1 Discussion—
Internationally, “electric strength” is used almost universally.
3.1.5 flashover, flashover (as related to electrical), n—a disruptive electrical discharge at an electrical discharge between two
electrodes which occurs around the surface of electrical insulation ora solid dielectric in the surrounding medium, which may or
may not cause permanent damage to the insulation.medium.
3.1.6 For definitions of other terms relating to solid insulating materials, refer to Terminology D1711.
4. Summary of Test Method
4.1 Alternating voltage at a commercial power frequency (60 Hz, unless otherwise specified) is applied to a test specimen. The
voltage is increased from zero or from a level well below the breakdown voltage, in one of three prescribed methods of voltage
application, until dielectric failure of the test specimen occurs.
4.2 Most commonly, the test voltage is applied using simple test electrodes on opposite faces of specimens. The options for the
specimens are that they be molded or cast, or cut from flat sheet or plate. Other electrode and specimen configurations are also
suitable for use to accommodate the geometry of the sample material, or to simulate a specific application for which the material
is being evaluated.
5. Significance and Use
5.1 The dielectric strength of an electrical insulating material is a property of interest for any application where an electrical
field will be present. In many cases the dielectric strength of a material will be the determining factor in the design of the apparatus
in which it is to be used.
5.2 Tests made as specified herein are suitable for use to provide part of the information needed for determining suitability of
a material for a given application; and also, for detecting changes or deviations from normal characteristics resulting from
processing variables, aging conditions, or other manufacturing or environmental situations. This test method is useful for process
control, acceptance or research testing.
The last approved version of this historical standard is referenced on www.astm.org.
Available from International Electrotechnical Commission (IEC), 3 rue de Varembé, Case postale 131, CH-1211, Geneva 20, Switzerland, http://www.iec.ch.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
D149 − 20
5.3 Results obtained by this test method can seldom be used directly to determine the dielectric behavior of a material in an
actual application. In most cases it is necessary that these results be evaluated by comparison with results obtained from other
functional tests or from tests on other materials, or both, in order to estimate their significance for a particular material.
5.4 Three methods for voltage application are specified in Section 12: Method A, Short-Time Test; Method B, Step-by-Step
Test; and Method C, Slow Rate-of-Rise Test. Method A is the most commonly-used test for quality-control tests. However, the
longer-time tests, Methods B and C, which usually will give lower test results, will potentially give more meaningful results when
different materials are being compared with each other. If a test set with motor-driven voltage control is available, the slow
rate-of-rise test is simpler and preferable to the step-by-step test. The results obtained from Methods B and C are comparable to
each other.
5.5 Documents specifying the use of this test method shall also specify:
5.5.1 Method of voltage application,
5.5.2 Voltage rate-of-rise, if slow rate-of-rise method is specified,
5.5.3 Specimen selection, preparation, and conditioning,
5.5.4 Surrounding medium and temperature during test,
5.5.5 Electrodes,
5.5.6 Wherever possible, the failure criterion of the current-sensing element, and
5.5.7 Any desired deviations from the recommended procedures as given.
5.6 If any of the requirements listed in 5.5 are missing from the specifying document, then the recommendations for the several
variables shall be followed.
5.7 Unless the items listed in 5.5 are specified, tests made with such inadequate reference to this test method are not in
conformance with this test method. If the items listed in 5.5 are not closely controlled during the test, it is possible that the
precisions stated in 15.2 and 15.3 will not be obtained.
5.8 Variations in the failure criteria (current setting and response time) of the current sensing element significantly affect the test
results.
5.9 Appendix X1. contains a more complete discussion of the significance of dielectric strength tests.
6. Apparatus
6.1 Voltage Source—Obtain the test voltage from a step-up transformer supplied from a variable sinusoidal low-voltage source.
The transformer, its voltage source, and the associated controls shall have the following capabilities:
6.1.1 The ratio of crest to root-mean-square (rms) test voltage shall be equal to =265% 1.34 to 1.48 , with the test specimen in
~ !
the circuit, at all voltages greater than 50 % of the breakdown voltage.
6.1.2 The capacity of the source shall be sufficient to maintain the test voltage until dielectric breakdown occurs. For most
materials, using electrodes similar to those shown in Table 1, an output current capacity of 40 mA is usually satisfactory. For more
complex electrode structures, or for testing high-loss materials, it is possible that higher current capacity will be needed. The power
rating for most tests will vary from 0.5 kVA for testing low-capacitance specimens at voltages up to 10 kV, to 5 kVA for voltages
up to 100 kV.
6.1.3 The controls on the variable low-voltage source shall be capable of varying the supply voltage and the resultant test
voltage smoothly, uniformly, and without overshoots or transients, in accordance with 12.2. Do not allow the peak voltage to
exceed 1.48 times the indicated rms test voltage under any circumstance. Motor-driven controls are preferable for making
short-time (see 12.2.1) or slow-rate-of-rise (see 12.2.3) tests.
6.1.4 Equip the voltage source with a circuit-breaking device that will operate within three cycles. The device shall disconnect
the voltage-source equipment from the power service and protect it from overload as a result of specimen breakdown causing an
overload of the testing apparatus. If prolonged current follows breakdown it will result in unnecessary burning of the test
specimens, pitting of the electrodes, and contamination of any liquid surrounding medium.
6.1.5 It is important for the circuit-breaking device to have an adjustable current-sensing element in the step-up transformer
secondary, to allow for adjustment consistent with the specimen characteristics and arranged to sense specimen current. Set the
sensing element to respond to a current that is indicative of specimen breakdown as defined in 12.3.
6.1.6 The current setting is likely to have a significant effect on the test results. Make the setting high enough that transients,
such as partial discharges, will not trip the breaker but not so high that excessive burning of the specimen, with resultant electrode
damage, will occur on breakdown. The optimum current setting is not the same for all specimens and depending upon the intended
use of the material and the purpose of the test, it is often desirable to make tests on a given sample at more than one current setting.
The electrode area is likely to have a significant effect upon the choice of current setting.
6.1.7 It is possible that the specimen current-sensing element will be in the primary of the step-up transformer. Calibrate the
current-sensing dial in terms of specimen current.
D149 − 20
A
TABLE 1 Typical Electrodes for Dielectric Strength Testing of Various Types of Insulating Materials
Electrode
B,C
Description of Electrodes Insulating Materials
Type
1 Opposing cylinders 51 mm (2 in.) in diameter, 25 mm (1 in.) thick with flat sheets of paper, films, fabrics, rubber, molded plastics, laminates,
edges rounded to 6.4 mm (0.25 in.) radius boards, glass, mica, and ceramic
2 Opposing cylinders 25 mm (1 in.) in diameter, 25 mm (1 in.) thick with same as for Type 1, particularly for glass, mica, plastic, and ceramic
edges rounded to 3.2 mm (0.125 in.) radius
3 Opposing cylindrical rods 6.4 mm (0.25 in.) in diameter with edges same as for Type 1, particularly for varnish, plastic, and other thin film and
D
rounded to 0.8 mm (0.0313 in.) radius tapes: where small specimens necessitate the use of smaller electrodes,
or where testing of a small area is desired
4 Flat plates 6.4 mm (0.25 in.) wide and 108 mm (4.25 in.) long with edges same as for Type 1, particularly for rubber tapes and other narrow widths
square and ends rounded to 3.2 mm (0.125 in.) radius of thin materials
E
5 Hemispherical electrodes 12.7 mm (0.5 in.) in diameter filling and treating compounds, gels and semisolid compounds and greases,
embedding, potting, and encapsulating materials
6 Opposing cylinders; the lower one 75 mm (3 in.) in diameter, 15 mm same as for Types 1 and 2
(0.60 in.) thick; the upper one 25 mm (1 in.) in diameter, 25 mm
F
thick; with edges of both rounded to 3 mm (0.12 in.) radius
G
7 Opposing circular flat plates, 150 mm diameter , 10 mm thick with flat sheet, plate, or board materials, for tests with the voltage gradient
H
edges rounded to 3 to 5 mm radius
parallel to the surface
A
These electrodes are those most commonly specified or referenced in ASTM standards. With the exception of Type 5 electrodes, no attempt has been made to suggest
electrode systems for other than flat surface material. It is acceptable to use other electrodes as specified in ASTM standards or as agreed upon between seller and
purchaser where none of these electrodes in the table is suitable for proper evaluation of the material being tested.
B
Electrodes are normally made from either brass or stainless steel. Reference shall be made to the standard governing the material to be tested to determine which, if
either, material is preferable.
C
The electrodes surfaces shall be polished and free from irregularities resulting from previous testing.
D
Refer to the appropriate standard for the load force applied by the upper electrode assembly. Unless otherwise specified the upper electrodes shall be 50 ± 2 g.
E
Refer to the appropriate standard for the proper gap settings.
F
The Type 6 electrodes are those given in IEC Publication 243-1 for testing of flat sheet materials. They are less critical as to concentricity of the electrodes than are the
Types 1 and 2 electrodes.
G
It is acceptable to use other diameters, provided that all parts of the test specimen are at least 15 mm inside the edges of the electrodes.
H G
The Type 7 electrodes, as described in the table and in Note , are those given in IEC Publication 243-1 for making tests parallel to the surface.
6.1.8 Exercise care in setting the response of the current control. If the control is set too high, the circuit will not respond when
breakdown occurs; if set too low, it is possible that it will respond to leakage currents, capacitive currents, or partial discharge
(corona) currents or, when the sensing element is located in the primary, to the step-up transformer magnetizing current.
6.2 Voltage Measurement—A voltmeter must be provided for measuring the rms test voltage. If a peak-reading voltmeter is
used, divide the reading by =2 to get rms values. The overall error of the voltage-measuring circuit shall not exceed 5 % of the
measured value. In addition, the response time of the voltmeter shall be such that its time lag will not be greater than 1 % of full
scale at any rate-of-rise used.
6.2.1 Measure the voltage using a voltmeter or potential transformer connected to the specimen electrodes, or to a separate
voltmeter winding, on the test transformer, that is unaffected by the step-up transformer loading.
6.2.2 It is desirable for the reading of the maximum applied test voltage to be retained on the voltmeter after breakdown so that
the breakdown voltage can be accurately read and recorded.
6.3 Electrodes—For a given specimen configuration, it is possible that the dielectric breakdown voltage will vary considerably,
depending upon the geometry and placement of the test electrodes. For this reason it is important that the electrodes to be used
be described when specifying this test method, and that they be described in the report.
6.3.1 One of the electrodes listed in Table 1 shall be specified by the document referring to this test method. If no electrodes
have been specified, select an applicable one from Table 1, or use other electrodes mutually acceptable to the parties concerned
when the standard electrodes cannot be used due to the nature or configuration of the material being tested. See references in
Appendix X2 for examples of some special electrodes. In any event the electrodes must be described in the report.
6.3.2 The electrodes of Types 1 through 4 and Type 6 of Table 1 shall be in contact with the test specimen over the entire flat
area of the electrodes.
6.3.3 The specimens tested using Type 7 electrodes shall be of such size that all portions of the specimen will be within and
no less than 15 mm from the edges of the electrodes during test. In most cases, tests using Type 7 electrodes are made with the
plane of the electrode surfaces in a vertical position. Tests made with horizontal electrodes shall not be directly compared with tests
made with vertical electrodes, particularly when the tests are made in a liquid surrounding medium.
6.3.4 Keep the electrode surfaces clean and smooth, and free from projecting irregularities resulting from previous tests. If
asperities have developed, they must be removed.
6.3.5 It is important that the original manufacture and subsequent resurfacing of electrodes be done in such a manner that the
specified shape and finish of the electrodes and their edges are maintained. The flatness and surface finish of the electrode faces
must be such that the faces are in close contact with the test specimen over the entire area of the electrodes. Surface finish is
particularly important when testing very thin materials which are subject to physical damage from improperly finished electrodes.
When resurfacing, do not change the transition between the electrode face and any specified edge radius.
D149 − 20
6.3.6 Whenever the electrodes are dissimilar in size or shape, ensure that the one at which the lowest concentration of stress
exists, usually the larger in size and with the largest radius, is at ground potential.
6.3.7 In some special cases liquid metal electrodes, foil electrodes, metal shot, water, or conductive coating electrodes are used.
It must be recognized that it is possible that these will give results differing widely from those obtained with other types of
electrodes.
6.3.8 Because of the effect of the electrodes on the test results, it is frequently possible to obtain additional information as to
the dielectric properties of a material (or a group of materials) by running tests with more than one type of electrode. This technique
is of particular value for research testing.
6.4 Surrounding Medium—The document calling for this test method needs to specify the surrounding medium and the test
temperature. Since flashover must be avoided and the effects of partial discharges prior to breakdown mimimized, even for short
time tests, it is often preferable and sometimes necessary to make the tests in insulating liquid (see 6.4.1). Breakdown values
obtained in insulating liquid are often not comparable with those obtained in air. The nature of the insulating liquid and the degree
of previous use are factors influencing the test values. In some cases, testing in air will require excessively large specimens or cause
heavy surface discharges and burning before breakdown. Some electrode systems for testing in air make use of pressure gaskets
around the electrodes to prevent flashover. The material of the gaskets or seals around the electrodes has the potential to influence
the breakdown values.
6.4.1 When tests are made in insulating oil, an oil bath of adequate size shall be provided. (Warning—The use of glass
containers is not recommended for tests at voltages above about 10 kV, because the energy released at breakdown has the potential
to be sufficient to shatter the container. Metal baths must be grounded.)
It is recommended that mineral oil meeting the requirements of Specification D3487, Type I or II, be used. It shall have a
dielectric breakdown voltage as determined by Test Method D877 of at least 26 kV. Other dielectric fluids are suitable for use as
surrounding mediums if specified. These include, but are not limited to, silicone fluids and other liquids intended for use in
transformers, circuit breakers, capacitors, or cables.
6.4.1.1 The quality of the insulating oil has the potential to have an appreciable effect upon the test results. In addition to the
dielectric breakdown voltage, mentioned above, particulate contaminants are especially important when very thin specimens (25
μm (1 mil) or less) are being tested. Depending upon the nature of the oil and the properties of the material being tested, other
properties, including dissolved gas content, water content, and dissipation factor of the oil also have the potential to affect the
results. Frequent replacement of the oil, or the use of filters and other reconditioning equipment is important to minimize the effect
of variations of the quality of the oil on the test results.
6.4.1.2 Breakdown values obtained using liquids having different electrical properties are often not comparable. (See X1.4.7.)
If tests are to be made at other than room temperature, the bath must be provided with a means for heating or cooling the liquid,
and with a means to ensure uniform temperature. Small baths can in some cases be placed in an oven (see 6.4.2) in order to provide
temperature control. If forced circulation of the fluid is provided, care must be taken to prevent bubbles from being whipped into
the fluid. The temperature shall be maintained within 65°C of the specified test temperature at the electrodes, unless otherwise
specified. In many cases it is specified that specimens to be tested in insulating oil are to be previously impregnated with the oil
and not removed from the oil before testing (see Practice D2413). For such materials, the bath must be of such design that it will
not be necessary to expose the specimens to air before testing.
6.4.2 If tests in air are to be made at other than ambient temperature or humidity, an oven or controlled humidity chamber must
be provided for the tests. Ovens meeting the requirements of Specification D5423 and provided with means for introducing the
test voltage will be suitable for use when only temperature is to be controlled.
6.4.3 Tests in gasses other than air will generally require the use of chambers that can be evacuated and filled with the test gas,
usually under some controlled pressure. The design of such chambers will be determined by the nature of the test program to be
undertaken.
6.5 Test Chamber—The test chamber or area in which the tests are to be made shall be of sufficient size to hold the test
equipment, and shall be provided with interlocks to prevent accidental contact with any electrically energized parts. A number of
different physical arrangements of voltage source, measuring equipment, baths or ovens, and electrodes are possible, but it is
essential that (1) all gates or doors providing access to spaces in which there are electrically energized parts be interlocked to shut
off the voltage source when opened; (2) clearances are sufficiently large that the field in the area of the electrodes and specimen
are not distorted and that flashovers and partial discharges (corona) do not occur except between the test electrodes; and (3)
insertion and replacement of specimens between tests be as simple and convenient as possible. Visual observation of the electrodes
and test specimen during the test is frequently desirable.
7. Hazards
7.1 Warning—It is possible that lethal voltages will be present during this test. It is essential that the test apparatus, and all
associated equipment electrically connected to it, be properly designed and installed for safe operation. Solidly ground all
electrically conductive parts that any person might come into contact with during the test. Provide means for use at the completion
of any test to ground any parts which fall into any of the following cases: (a) were at high voltage during the test; (b) have the
potential to acquire an induced charge during the test; or (c) have the potential to retain a charge even after disconnection of the
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voltage source. Thoroughly instruct all operators in the proper way to conduct tests safely. When making high-voltage tests,
particularly in compressed gas or in oil, it is possible that the energy released at breakdown will be sufficient to result in fire,
explosion, or rupture of the test chamber. Design test equipment, test chambers, and test specimens so as to minimize the possibility
of such occurrences and to eliminate the possibility of personal injury.
7.2 Warning—Ozone is a physiologically hazardous gas at elevated concentrations. The exposure limits are set by
governmental agencies and are usually based upon recommendations made by the American Conference of Governmental
Industrial Hygienists. Ozone is likely to be present whenever voltages exist which are sufficient to cause partial, or complete,
discharges in air or other atmospheres that contain oxygen. Ozone has a distinctive odor which is initially discernible at low
concentrations but sustained inhalation of ozone can cause temporary loss of sensitivity to the scent of ozone. Because of this it
is important to measure the concentration of ozone in the atmosphere, using commercially available monitoring devices, whenever
the odor of ozone is persistently present or when ozone generating conditions continue. Use appropriate means, such as exhaust
vents, to reduce ozone concentrations to acceptable levels in working areas.
8. Sampling
8.1 The detailed sampling procedure for the material being tested needs to be defined in the specification for that material.
8.2 Sampling procedures for quality control purposes shall provide for gathering of sufficient samples to estimate both the
average quality and the variability of the lot being examined; and for proper protection of the samples from the time they are taken
until the preparation of the test specimens in the laboratory or other test area is begun.
8.3 For the purposes of most tests it is desirable to take samples from areas that are not immediately adjacent to obvious defects
or discontinuities in the material. Avoid the outer few layers of roll material, the top sheets of a package of sheets, or material
immediately next to an edge of a sheet or roll, unless the presence or proximity of defects or discontinuities is of interest in the
investigation of the material.
8.4 The sample shall be large enough to permit making as many individual tests as required for the particular material (see 12.4).
9. Test Specimens
9.1 Preparation and Handling:
9.1.1 Prepare specimens from samples collected in accordance with Section 8.
9.1.2 When flat-faced electrodes are to be used, the surfaces of the specimens which will be in contact with the electrodes shall
be smooth parallel planes, insofar as possible without actual surface machining.
9.1.3 The specimens shall be of sufficient size to prevent flashover under the conditions of test. For thin materials it will often
be convenient to use specimens large enough to permit making more than one test on a single piece.
9.1.4 For thicker materials (usually more than 2 mm thick) it is possible that the breakdown strength will be high enough that
flashover or intense surface partial discharges (corona) will occur prior to breakdown. Techniques that are suitable for use to
prevent flashover, or to reduce partial discharge (corona) include:
9.1.4.1 Immerse the specimen in insulating oil during the test. See X1.4.7 for the surrounding medium factors influencing
breakdown. This is often necessary for specimens that have not been dried and impregnated with oil, as well as for those which
have been prepared in accordance with Practice D2413, for example. (See 6.4.)
9.1.4.2 Machine a recess or drill a flat-bottom hole in one or both surfaces of the specimen to reduce the test thickness. If
dissimilar electrodes are used (such as Type 6 of Table 1) and only one surface is to be machined, the larger of the two electrodes
shall be in contact with the machined surface. Care must be taken in machining specimens not to contaminate or mechanically
damage them.
9.1.4.3 Apply seals or shrouds around the electrodes, in contact with the specimen to reduce the tendency to flashover.
9.1.5 Materials that are not in flat sheet form shall be tested using specimens (and electrodes) appropriate to the material and
the geometry of the sample. It is essential that for these materials both the specimen and the electrodes be defined in the
specification for the material.
9.1.6 Whatever the form of the material, if tests of other than surface-to-surface puncture strength are to be made, define the
specimens and the electrodes in the specification for the material.
9.2 In nearly all cases the actual thickness of the test specimen is important. Unless otherwise specified, measure the thickness
after the test in the immediate vicinity of the area of breakdown. Measurements shall be made at room temperature (25 6 5°C),
using the appropriate procedure of Test Methods D374.
10. Calibration
10.1 In making calibration measurements, take care that the values of voltage at the electrodes can be determined within the
accuracy given in 6.2, with the test specimens in the circuit.
Available from American Conference of Governmental Industrial Hygienists, Inc. (ACGIH), 1330 Kemper Meadow Dr., Cincinnati, OH 45240, http://www.acgih.org.
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10.2 Use an independently calibrated
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