ASTM D3755-20

Standard Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials Under Direct-Voltage Stress

SIGNIFICANCE AND USE
5.1 This test method is intended for use as a control and acceptance test for direct-voltage applications. It can also be used in the partial evaluation of material for specific end uses and as a means for detecting changes in material due to specific deteriorating causes.  
5.2 Experience indicates that the breakdown value obtained with direct voltage usually will be approximately 2 to 4 times the rms value of the 60-Hz alternating-voltage breakdown.  
5.3 For a nonhomogeneous test specimen, the distribution of voltage stress within the specimen is determined by impedance (largely capacitive) with alternating voltage. With an increasing direct voltage, the voltage distribution will still be largely capacitive, although this depends partly on the rate of voltage increase. After steady application of direct voltage the voltage division across the test specimen is determined by resistance. The choice of direct or alternating voltage depends upon the purpose for which the breakdown test is to be used, and to some extent, on the intended application of the material.  
5.4 A more complete discussion of the significance of dielectric breakdown tests is given in Appendix X1 of this method and in Appendix X1 of Test Method D149. Those appendix sections of Test Method D149 that refer to alternating voltage are not applicable to the direct-voltage method.
SCOPE
1.1 This test method covers the determination of dielectric breakdown voltage and dielectric strength of solid electrical insulating materials under direct-voltage stress.  
1.2 Since some materials require special treatment, reference shall also be made to ASTM specifications or to the test method directly applicable to the material to be tested. See Test Method D149 for the determination of dielectric strength of electrical insulating materials at commercial power frequencies.  
1.3 This test method is similar to IEC Publication 243-2. All procedures in this test method are included in IEC 243-2. Differences between this test method and IEC 243-2 are largely editorial.  
1.4 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 applicability of regulatory limitations prior to use. Specific precaution statements are given in Section 7.  
1.5 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: 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 D3755-14 - Standard Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials Under Direct-Voltage Stress
• Effective Date: 01-Jan-2020
• Refers: ASTM D1711-24 - Standard Terminology Relating to Electrical Insulation
• Effective Date: 01-Mar-2024
• Refers: ASTM D149-20 - 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 D3487-16e1 - Standard Specification for Mineral Insulating Oil Used in Electrical Apparatus
• Effective Date: 15-Jun-2016
• Refers: ASTM D3487-16 - 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 D176-07(2012) - Standard Test Methods for Solid Filling and Treating Compounds Used for Electrical Insulation (Withdrawn 2013)
• Effective Date: 01-Apr-2012
• 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 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 D3755-20: Standard Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials Under Direct-Voltage Stress provides a method for determining the dielectric breakdown voltage and dielectric strength of solid electrical insulating materials when subjected to direct-voltage (DC) stress. Developed by ASTM International, this standard is widely utilized for control, acceptance, and partial evaluation of electrical insulating materials, and for detecting changes in performance due to material deterioration. This test is particularly crucial for ensuring reliability in applications where electrical insulation will encounter direct-voltage conditions.

Key Topics

• Dielectric Breakdown Voltage & Strength: Defines key measures for evaluating an insulating material’s ability to withstand electrical stress without failure under direct voltage.
• Test Apparatus & Conditions:
  • Use of specialized high-voltage DC sources, grounded enclosures, and appropriately selected electrodes.
  • Specimen conditioning regarding temperature and humidity to reflect potential use environments.
• Safety Precautions: Emphasizes strict safety procedures due to the presence of lethal voltages and the potential generation of hazardous ozone gas.
• Criteria for Breakdown:
  • Identifies proper signs of failure such as sudden current increase, flashover, and visible material breakdown.
  • Recommends repeating tests to confirm if ambiguous results occur.
• Factors Impacting Results:
  • Thickness and homogeneity of specimens, electrode configuration, environmental conditions (temperature, humidity), and the nature of the surrounding medium (gas or oil).
• Reporting Requirements: Specifies details to include-such as specimen thickness, breakdown voltage data, environmental conditions, conditioning, electrode setup, and medium.

Applications

ASTM D3755-20 is used in a variety of industries to assess the electrical insulating properties of solid materials intended for use under DC voltage:

• Quality Control and Material Acceptance: Ensures that insulating components, such as plastics, composites, or ceramics, meet specified performance criteria before deployment in electrical equipment.
• Research and Development: Supports material selection and formulation in the development of new insulating materials or blends.
• Aging and Deterioration Studies: Detects the impact of long-term stress, thermal aging, or exposure to contaminants on dielectric performance.
• Comparative Evaluation: Allows engineering teams to compare material performance under DC stress with known standards or benchmarks.
• Compliance Assessment: Demonstrates conformance to internal or regulatory requirements when direct-voltage electrical conditions are expected in service.

The test procedure is adaptable for both thin and thick specimens, with modifications to prevent surface flashover during high-voltage testing, such as testing in oil for high-voltage or thick samples.

Related Standards

ASTM D3755-20 aligns closely with a number of other significant standards in the field of electrical insulation testing:

• ASTM D149 – Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials at Commercial Power Frequencies (AC testing counterpart).
• IEC 243-2 – Methods of Test for Electric Strength of Solid Insulating Materials – Part 2: Additional Requirements for Tests Using Direct Voltage (international equivalent, largely editorial differences).
• ANSI C68.1/IEEE Std 4 – Techniques for Dielectric Tests, providing guidelines for voltage application and measurement.

Further, ASTM D1711 offers standardized terminology for the field, and ASTM D3487 covers specifications for mineral insulating oils used during testing.

Practical Value

By providing a structured and repeatable procedure for measuring dielectric breakdown voltage and strength under direct voltage, ASTM D3755-20 supports manufacturers, quality assurance teams, and researchers in:

• Ensuring safety and reliability in electrical equipment
• Detecting early material weaknesses or deterioration
• Satisfying market and regulatory requirements concerning electrical insulation performance

This standard thus plays an essential role in safeguarding electrical systems where solid insulation is exposed to direct-voltage stress.

Keywords: dielectric breakdown voltage, dielectric strength, solid electrical insulating materials, DC voltage, electrical insulation testing, ASTM D3755, direct-voltage stress, quality control.

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: D3755 − 20
Standard Test Method for
Dielectric Breakdown Voltage and Dielectric Strength of
Solid Electrical Insulating Materials Under Direct-Voltage
Stress
This standard is issued under the fixed designation D3755; 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.
1. Scope* DielectricStrengthofSolidElectricalInsulatingMaterials
at Commercial Power Frequencies
1.1 This test method covers the determination of dielectric
D176 Test Methods for Solid Filling and Treating Com-
breakdown voltage and dielectric strength of solid electrical
pounds Used for Electrical Insulation (Withdrawn 2013)
insulating materials under direct-voltage stress.
D877 Test Method for Dielectric Breakdown Voltage of
1.2 Since some materials require special treatment, refer-
Insulating Liquids Using Disk Electrodes
ence shall also be made to ASTM specifications or to the test
D1711 Terminology Relating to Electrical Insulation
methoddirectlyapplicabletothematerialtobetested.SeeTest
D2436 Specification for Forced-Convection Laboratory Ov-
Method D149 for the determination of dielectric strength of 3
ens for Electrical Insulation (Withdrawn 1994)
electrical insulating materials at commercial power frequen-
D3487 Specification for Mineral Insulating Oil Used in
cies.
Electrical Apparatus
1.3 ThistestmethodissimilartoIECPublication243-2.All
2.2 ANSI Standard:
procedures in this test method are included in IEC 243-2.
ANSI C68.1 Techniques for Dielectric Tests, IEEE Standard
DifferencesbetweenthistestmethodandIEC243-2arelargely
No. 4.
editorial.
2.3 IEC Standard:
IEC 243-2 Methods of test for electric strength of solid
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the insulating materials—Part 2: Additional requirements for
tests using direct voltage
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
3. Terminology
mine the applicability of regulatory limitations prior to use.
Specific precaution statements are given in Section 7.
3.1 Definitions:
1.5 This international standard was developed in accor-
3.1.1 creepage distance, n—shortest distance between two
dance with internationally recognized principles on standard-
conductive parts (typically metal), measured along the surface
ization established in the Decision on Principles for the
of the dielectric insulator.
Development of International Standards, Guides and Recom-
3.1.2 dielectric breakdown voltage, n—Refer to Terminol-
mendations issued by the World Trade Organization Technical
ogy D1711.
Barriers to Trade (TBT) Committee.
3.1.3 dielectric strength, n—Refer to Terminology D1711.
2. Referenced Documents 3.1.4 flashover (as related to electrical), n—an electrical
discharge between two electrodes which occurs around the
2.1 ASTM Standards:
surface of a solid dielectric in the surrounding medium.
D149 Test Method for Dielectric Breakdown Voltage and
4. Summary of Test Method
4.1 The specimen, held in a properly designed electrode
This test method is under the jurisdiction of ASTM Committee D09 on
Electrical and Electronic Insulating Materials and is the direct responsibility of
system, is electrically stressed by the application of an increas-
Subcommittee D09.12 on Electrical Tests.
ing direct voltage until internal breakdown occurs. The test
Current edition approved Jan. 1, 2020. Published January 2020. Originally
approved in 1979. Last previous edition approved in 2014 as D3755 – 14. DOI:
10.1520/D3755-20.
2 3
For referenced ASTM standards, visit the ASTM website, www.astm.org, or The last approved version of this historical standard is referenced on
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM www.astm.org.
Standards volume information, refer to the standard’s Document Summary page on Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
the ASTM website. 4th Floor, New York, NY 10036.
*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
D3755 − 20
voltage is applied at a uniform rate of increase. The direct that the measurement error will not exceed 62 % of full scale
voltage is obtained from a high-voltage supply of adequate and be in accordance with ANSI C68.1.
current capacity and regulation, reasonably ripple-free, with
6.4 Electrodes:
facilities for measuring and controlling the output voltage.
6.4.1 For those cases when the insulating material is in the
form of flat sheet or tape, or is of the nature of a semisolid (for
5. Significance and Use
example, grease potting material, and so forth) the electrodes
shall be selected from those listed in Table 1 of Test Method
5.1 This test method is intended for use as a control and
D149. The electrode contact pressure shall be adequate to
acceptance test for direct-voltage applications. It can also be
obtain good electrical contact.
used in the partial evaluation of material for specific end uses
andasameansfordetectingchangesinmaterialduetospecific 6.4.2 Where excellent electrode contact is considered
important, use paint or vaporized metal electrodes. Such
deteriorating causes.
electrodesshallalsobeusedwhenspecimengeometryprevents
5.2 Experience indicates that the breakdown value obtained
the use of rigid, solid metal electodes. It is possible that the
with direct voltage usually will be approximately 2 to 4 times
results obtained with painted or sprayed electrodes will not be
the rms value of the 60-Hz alternating-voltage breakdown.
comparable with those obtained using other types of elec-
5.3 For a nonhomogeneous test specimen, the distribution
trodes.
of voltage stress within the specimen is determined by imped-
6.5 Test Chamber—For tests under other than ambient
ance (largely capacitive) with alternating voltage. With an
conditions, the specimen must be placed in a suitable environ-
increasing direct voltage, the voltage distribution will still be
mental chamber of adequate size. For tests at elevated
largely capacitive, although this depends partly on the rate of
temperatures, an oven that meets the requirements of Specifi-
voltage increase. After steady application of direct voltage the
cation D2436 will be convenient. The test chamber must be
voltage division across the test specimen is determined by
equipped with safety devices (Section 7).
resistance. The choice of direct or alternating voltage depends
6.6 Ground Switch—The power supply shall be equipped
upon the purpose for which the breakdown test is to be used,
with a grounding switch that is gravity operated and designed
and to some extent, on the intended application of the material.
to close in less than 0.5 s. The grounding switch shall connect
5.4 A more complete discussion of the significance of
the high-voltage output terminal of the power supply and
dielectric breakdown tests is given in Appendix X1 of this
ground terminal through a low resistance when the input
method and in Appendix X1 of Test Method D149. Those
supply power is removed or the test chamber door is opened.
appendixsectionsofTestMethodD149thatrefertoalternating
voltage are not applicable to the direct-voltage method.
7. Safety Precautions
7.1 Warning—Lethalvoltagesareapotentialhazardduring
6. Apparatus
the performance of this test. It is essential that the test
6.1 Basic Direct-Voltage Power Supplies, or dielectric test
apparatus, and all associated equipment electrically connected
sets of various voltage ratings, which can operate with one of
to it, be properly designed and installed for safe operation.
the two output terminals grounded, are commonly available
Solidly ground all electrically conductive parts that a person
commercially. Such apparatus customarily includes the neces-
can contact during the test. Provide means for use at the
sary voltage-control, voltage-measuring, and circuit-
completion of any test to ground any parts that were at high
interrupting equipment. A provision for retaining the break-
voltage during the test or have the potential for acquiring an
down voltage reading after breakdown is desirable.
induced charge during the test or retaining a charge even after
6.1.1 For a direct voltage derived from a rectified and
disconnecting the voltage source. Thoroughly instruct all
filtered power frequency source, ripple on the output voltage
operators as to the correct procedures for performing tests
shall be less than 1 %. The criterion is met if the time constant
safely. When making high-voltage tests, particularly in com-
of the circuit is at least 0.4 s. The time constant is product of
pressed gas or in oil, it is possible for the energy released at
the filter capacitance plus the specimen capacitance in
breakdown to be sufficient to result in fire, explosion, or
microfarads, and the specimen insulation resistance (in mega-
rupture of the test chamber. Design test equipment, test
ohms) corresponding to the parallel combination of the volt-
chambers, and test specimens so as to minimize the possibility
meter circuit resistance and the specimen resistance.
of such occurrences and to eliminate the possibility of personal
6.2 Voltage Control, that will enable the test voltage to be
injury. If the potential for fire exists, have fire suppression
increased at a linear rate. Preference shall be given to a equipment available.
variable-speed motor-driven voltage control over a manual
7.2 When a direct-voltage test has been applied to the test
control.Therate-of-riseoftestvoltageshallnotvarymorethan
specimen, both the specimen and power supply can remain
620 % from the specified rate at any point.
charged after the test voltage source has been de-energized.
6.3 Voltmeter, to measure the voltage directly applied to the This will present a hazard to test personnel. Direct-voltage
electrode system. The response of the voltmeter shall be such testing is more hazardous than testing with alternating voltage,
that its time lag shall not introduce an error greater than 1 % of where the charge on the specimen is rapidly dissipated in the
full scale at any rate-of-rise used. The overall accuracy of the low-impedance winding of the test transformer after the test is
voltmeter and the voltage-measuring device used shall be such de-energized.
D3755 − 20
7.3 The test specimen and high-voltage output of the power 9. Test Specimens
supply must be enclosed in a grounded metallic screen.Access
9.1 Foradescriptionoftestspecimensofmaterialsandtheir
to the test enclosure must be dependent upon prior grounding
preparation, refer to the ASTM methods applicable to the
ofthepowersupplyandtestspecimenthroughalowresistance
materials to be tested.
as referred to in 6.6.
9.2 Providespecimensthatarerepresentativeofthematerial
7.4 A manual grounding stick must be used to completely
to be tested. Prepare enough specimens to permit making five
discharge the test specimen and power supply after the test and
tests. In the preparation of test specimens from solid materials,
prior to handling them. The grounding stick shall be left in
take care that the surfaces in contact with the electrodes are
contact with the test specimen and high-voltage transformer
parallel and as plane and smooth as the material permits.
terminals for as long as feasible.
9.3 Thin Solid Materials (Sheets and Plates Less than 3 mm
7.5 Warning—Ozone is a physiologically hazardous gas at
Thick)—Prepare test specimens of sufficient area to prevent
elevated concentrations. Levels of acceptable industrial expo-
flashover under the conditions of test.
sure have been established by the American Conference of
9.4 Thick Solid Materials—The breakdown of thick solid
Government and Industrial Hygienists. Ozone has a distinc-
materials is generally so high that the specimen must be
tive odor that is initially discernible at low concentrations, but
immersed in insulating fluid to prevent flashover and to
temporary loss of the sense of smell can occur. It is likely to be
minimize partial discharge. See Section 13. Other techniques
present wherever voltages exist that are sufficient to cause
that can be used to prevent flashover are:
partial or complete discharges in air or other atmospheres
9.4.1 The machining of a recess in the test specimen for an
containing oxygen. When the odor of ozone is persistently
electrode.
present or when ozone generating conditions continue, the
9.4.2 The use of shrouds on the test specimen.
concentration of ozone in the atmosphere shall be measured
using commercially available monitoring devices.Appropriate
9.4.3 The application of a sealing apparatus under pressure
means, such as installation of exhaust vents, shall be taken to to the upper and lower faces of the test specimen.
maintain ozone concentrations in working areas within accept-
able levels. 10. Thickness
10.1 Thethicknessusedincomputingthedielectricstrength
8. Criteria of Breakdown
shall be the average thickness of the specimen measured as
8.1 Dielectric breakdown is generally accompanied by an
specified in the test method for the material involved. If not
increase in current in the test circuit that will activate a sensing
specified, the thickness measurement shall be made at room
element such as a circuit breaker, a fuse, or current-sensing
temperature of 25 6 5 °C.
circuit.Ifsensitivityoftheelementiswellcoordinatedwiththe
10.2 If the material is laminar or known to vary in dielectric
characteristics of the test equipment and the material under
strength with orientation, such as caused by graininess, the
test, its operation will be a positive indication of breakdown.
specimen shall be cut so that its thickness is in the direction of
8.2 Failureofacircuitbreakertooperateisnotbeapositive
the electric field under use conditions.
criterionoftheabsenceofbreakdown.Abreakercanfailtotrip
10.3 Whenthinmaterials,suchaslaminates,aretobetested
because it is set for too great a current or because of
inthedirectionoftheirwidthorlength,specialprocedureswill
malfunction. On the other hand, if the tripping circuit is set for
be needed to avoid flashover, s
...

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: D3755 − 14 D3755 − 20
Standard Test Method for
Dielectric Breakdown Voltage and Dielectric Strength of
Solid Electrical Insulating Materials Under Direct-Voltage
Stress
This standard is issued under the fixed designation D3755; 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.
1. Scope Scope*
1.1 This test method covers the determination of dielectric breakdown voltage and dielectric strength of solid electrical
insulating materials under direct-voltage stress.
1.2 Since some materials require special treatment, reference shall also be made to ASTM specifications or to the test method
directly applicable to the material to be tested. See Test Method D149 for the determination of dielectric strength of electrical
insulating materials at commercial power frequencies.
1.3 This test method is similar to IEC Publication 243-2. All procedures in this test method are included in IEC 243-2.
Differences between this test method and IEC 243-2 are largely editorial.
1.4 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 precaution statements are given in Section 7.
1.5 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:
D149 Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials at
Commercial Power Frequencies
D176 Test Methods for Solid Filling and Treating Compounds Used for Electrical Insulation (Withdrawn 2013)
D877 Test Method for Dielectric Breakdown Voltage of Insulating Liquids Using Disk Electrodes
D1711 Terminology Relating to Electrical Insulation
D2436 Specification for Forced-Convection Laboratory Ovens for Electrical Insulation (Withdrawn 1994)
D3487 Specification for Mineral Insulating Oil Used in Electrical Apparatus
2.2 ANSI Standard:
ANSI C68.1 Techniques for Dielectric Tests, IEEE Standard No. 4.
2.3 IEC Standard:
IEC 243-2 Methods of test for electric strength of solid insulating materials—Part 2: Additional requirements for tests using
direct voltage
3. Terminology
3.1 Definitions:
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 May 15, 2014Jan. 1, 2020. Published June 2014January 2020. Originally approved in 1979. Last previous edition approved in 20042014 as
D3755 – 97 (2004)D3755 – 14., which was withdrawn in January 2013 and reinstated in June 2014. DOI: 10.1520/D3755-14. DOI: 10.1520/D3755-20.
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.
The last approved version of this historical standard is referenced on www.astm.org.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036.
*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
D3755 − 20
3.1.1 creepage distance, n—shortest distance between two conductive parts (typically metal), measured along the surface of the
dielectric insulator.
3.1.2 dielectric breakdown voltage, n—Refer to Terminology D1711.
3.1.3 dielectric strength, n—Refer to Terminology D1711.
3.1.4 flashover, flashover (as related to electrical), n—Refer to Terminologyan electrical discharge D1711.between two
electrodes which occurs around the surface of a solid dielectric in the surrounding medium.
4. Summary of Test Method
4.1 The specimen, held in a properly designed electrode system, is electrically stressed by the application of an increasing direct
voltage until internal breakdown occurs. The test voltage is applied at a uniform rate of increase. The direct voltage is obtained
from a high-voltage supply of adequate current capacity and regulation, reasonably ripple-free, with facilities for measuring and
controlling the output voltage.
5. Significance and Use
5.1 This test method is intended for use as a control and acceptance test for direct-voltage applications. It can also be used in
the partial evaluation of material for specific end uses and as a means for detecting changes in material due to specific deteriorating
causes.
5.2 Experience indicates that the breakdown value obtained with direct voltage usually will be approximately 2 to 4 times the
rms value of the 60-Hz alternating-voltage breakdown.
5.3 For a nonhomogeneous test specimen, the distribution of voltage stress within the specimen is determined by impedance
(largely capacitive) with alternating voltage. With an increasing direct voltage, the voltage distribution will still be largely
capacitive, although this depends partly on the rate of voltage increase. After steady application of direct voltage the voltage
division across the test specimen is determined by resistance. The choice of direct or alternating voltage depends upon the purpose
for which the breakdown test is to be used, and to some extent, on the intended application of the material.
5.4 A more complete discussion of the significance of dielectric breakdown tests is given in Appendix X1 of this method and
in Appendix X1 of Test Method D149. Those appendix sections of Test Method D149 that refer to alternating voltage are not
applicable to the direct-voltage method.
6. Apparatus
6.1 Basic Direct-Voltage Power Supplies, or dielectric test sets of various voltage ratings, which can operate with one of the two
output terminals grounded, are commonly available commercially. Such apparatus customarily includes the necessary voltage-
control, voltage-measuring, and circuit-interrupting equipment. A provision for retaining the breakdown voltage reading after
breakdown is desirable.
6.1.1 For a direct voltage derived from a rectified and filtered power frequency source, ripple on the output voltage shall be less
than 1 %. The criterion is met if the time constant of the circuit is at least 0.4 s. The time constant is product of the filter capacitance
plus the specimen capacitance in microfarads, and the specimen insulation resistance (in megaohms) corresponding to the parallel
combination of the voltmeter circuit resistance and the specimen resistance.
6.2 Voltage Control, that will enable the test voltage to be increased at a linear rate. Preference shall be given to a variable-speed
motor-driven voltage control over a manual control. The rate-of-rise of test voltage shall not vary more than 620 % from the
specified rate at any point.
6.3 Voltmeter, to measure the voltage directly applied to the electrode system. The response of the voltmeter shall be such that
its time lag shall not introduce an error greater than 1 % of full scale at any rate-of-rise used. The overall accuracy of the voltmeter
and the voltage-measuring device used shall be such that the measurement error will not exceed 62 % of full scale and be in
accordance with ANSI C68.1.
6.4 Electrodes:
6.4.1 For those cases when the insulating material is in the form of flat sheet or tape, or is of the nature of a semisolid (for
example, grease potting material, and so forth) the electrodes shall be selected from those listed in Table 1 of Test Method D149.
The electrode contact pressure shall be adequate to obtain good electrical contact.
6.4.2 Where excellent electrode contact is considered important, use paint or vaporized metal electrodes. Such electrodes shall
also be used when specimen geometry prevents the use of rigid, solid metal electodes. It is possible that the results obtained with
painted or sprayed electrodes will not be comparable with those obtained using other types of electrodes.
6.5 Test Chamber—For tests under other than ambient conditions, the specimen must be placed in a suitable environmental
chamber of adequate size. For tests at elevated temperatures, an oven that meets the requirements of Specification D2436 will be
convenient. The test chamber must be equipped with safety devices (Section 7).
D3755 − 20
6.6 Ground Switch—The power supply shall be equipped with a grounding switch that is gravity operated and designed to close
in less than 0.5 s. The grounding switch shall connect the high-voltage output terminal of the power supply and ground terminal
through a low resistance when the input supply power is removed or the test chamber door is opened.
7. Safety Precautions
7.1 Warning—Lethal voltages are a potential hazard during the performance of 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 a person can contact during the test. Provide means for use at the completion of any test to ground
any parts that were at high voltage during the test or have the potential for acquiring an induced charge during the test or retaining
a charge even after disconnecting the voltage source. Thoroughly instruct all operators as to the correct procedures for performing
tests safely. When making high-voltage tests, particularly in compressed gas or in oil, it is possible for the energy released at
breakdown to 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. If the
potential for fire exists, have fire suppression equipment available.
7.2 When a direct-voltage test has been applied to the test specimen, both the specimen and power supply can remain charged
after the test voltage source has been de-energized. This will present a hazard to test personnel. Direct-voltage testing is more
hazardous than testing with alternating voltage, where the charge on the specimen is rapidly dissipated in the low-impedance
winding of the test transformer after the test is de-energized.
7.3 The test specimen and high-voltage output of the power supply must be enclosed in a grounded metallic screen. Access to
the test enclosure must be dependent upon prior grounding of the power supply and test specimen through a low resistance as
referred to in 6.6.
7.4 A manual grounding stick must be used to completely discharge the test specimen and power supply after the test and prior
to handling them. The grounding stick shall be left in contact with the test specimen and high-voltage transformer terminals for
as long as feasible.
7.5 Warning—Ozone is a physiologically hazardous gas at elevated concentrations. Levels of acceptable industrial exposure
have been established by the American Conference of Government and Industrial Hygienists. Ozone has a distinctive odor that
is initially discernible at low concentrations, but temporary loss of the sense of smell can occur. It is likely to be present wherever
voltages exist that are sufficient to cause partial or complete discharges in air or other atmospheres containing oxygen. When the
odor of ozone is persistently present or when ozone generating conditions continue, the concentration of ozone in the atmosphere
shall be measured using commercially available monitoring devices. Appropriate means, such as installation of exhaust vents, shall
be taken to maintain ozone concentrations in working areas within acceptable levels.
8. Criteria of Breakdown
8.1 Dielectric breakdown is generally accompanied by an increase in current in the test circuit that will activate a sensing
element such as a circuit breaker, a fuse, or current-sensing circuit. If sensitivity of the element is well coordinated with the
characteristics of the test equipment and the material under test, its operation will be a positive indication of breakdown.
8.2 Failure of a circuit breaker to operate is not be a positive criterion of the absence of breakdown. A breaker can fail to trip
because it is set for too great a current or because of malfunction. On the other hand, if the tripping circuit is set for too low a
current, currents due to leakage or partial discharge (corona) will cause it to trip before breakdown voltage is reached.
8.3 Observe the specimen during the test to ascertain that tripping of the breaker or current-sensing circuit is not caused by
flashover. When flashover is a problem, it will be necessary to provide for more creepage distance around the electrodes, to
decrease specimen thickness, or to immerse the specimen in a liquid dielectric (Section 13).
8.4 Observation of actual rupture or decomposition is positive evidence of specimen breakdown. In test position, however, these
physical evidences of breakdown are not always apparent. If breakdown is in question it is common practice to repeat the test on
the same specimen. Breakdown is confirmed when reapplication of test voltage results in a substantially lower breakdown voltage.
9. Test Specimens
9.1 For a description of test specimens of materials and their preparation, refer to the ASTM methods applicable to the materials
to be tested.
9.2 Provide specimens that are representative of the material to be tested. Prepare enough specimens to permit making five tests.
In the preparation of test specimens from solid materials, take care that the surfaces in contact with the electrodes are parallel and
as plane and smooth as the material permits.
American Conference of Governmental Industrial Hygienists, Building D-7, 6500 Glenway Drive, Cincinnati, OH 45211.
D3755 − 20
9.3 Thin Solid Materials (Sheets and Plates Less than 3 mm Thick)—Prepare test specimens of sufficient area to prevent
flashover under the
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