ASTM D3755-97
(Test Method)Standard Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials Under Direct-Voltage Stress
Standard Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials Under Direct-Voltage Stress
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 should also be made to ASTM specifications or to the test method directly applicable to the material to be tested. See Test Method D 149 for the determination of dielectric strength of electrical insulating materials at commercial power frequencies.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
An American National Standard
Designation: D 3755 – 97
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 D 3755; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope Electrical Apparatus
2.2 ANSI Standard:
1.1 This test method covers the determination of dielectric
ANSI C68.1 Techniques for Dielectric Tests, IEEE Standard
breakdown voltage and dielectric strength of solid electrical
No. 4.
insulating materials under direct-voltage stress.
2.3 IEC Standard:
1.2 Since some materials require special treatment, refer-
IEC 243-2 Methods of test for electric strength of solid
ence should also be made to ASTM specifications or to the test
insulating materials—Part 2: Additional requirements for
method directly applicable to the material to be tested. See Test
tests using direct voltage
Method D 149 for the determination of dielectric strength of
electrical insulating materials at commercial power frequen-
3. Terminology
cies.
3.1 Definitions:
1.3 This test method is similar to IEC Publication 243-2. All
3.1.1 dielectric breakdown voltage, n—Refer to Terminol-
procedures in this test method are included in IEC 243-2.
ogy D 1711.
Differences between this test method and IEC 243-2 are largely
3.1.2 dielectric strength, n—Refer to Terminology D 1711.
editorial.
3.1.3 flashover, n—Refer to Terminology D 1711.
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
4. Summary of Test Method
responsibility of the user of this standard to establish appro-
4.1 The specimen, held in a properly designed electrode
priate safety and health practices and determine the applica-
system, is electrically stressed by the application of an increas-
bility of regulatory limitations prior to use. Specific precaution
ing direct voltage until internal breakdown occurs. The test
statements are given in Section 7.
voltage is applied at a uniform rate of increase. The direct
2. Referenced Documents voltage is obtained from a high-voltage supply of adequate
current capacity and regulation, reasonably ripple-free, with
2.1 ASTM Standards:
facilities for measuring and controlling the output voltage.
D 149 Test Method for Dielectric Breakdown Voltage and
Dielectric Strength of Solid Electrical Insulating Materials
5. Significance and Use
at Commercial Power Frequencies
5.1 This test method is intended for use as a control and
D 176 Test Methods for Solid Filling and Treating Com-
acceptance test for direct-voltage applications. It may be used
pounds Used for Electrical Insulation
also in the partial evaluation of material for specific end uses
D 877 Test Method for Dielectric Breakdown Voltage of
and as a means for detecting changes in material due to specific
Insulating Liquids Using Disk Electrodes
2 deteriorating causes.
D 1711 Terminology Relating to Electrical Insulation
5.2 Experience indicates that the breakdown value obtained
D 2436 Specification for Forced-Convection Laboratory
2 with direct voltage usually will be approximately 2 to 4 times
Ovens for Electrical Insulation
the rms value of the 60-Hz alternating-voltage breakdown.
D 3487 Specification for Mineral Insulating Oil Used in
5.3 For a nonhomogeneous test specimen, the distribution
of voltage stress within the specimen is determined by imped-
ance (largely capacitive) with alternating voltage. With an
This test method is under the jurisdiction of ASTM Committee D-9 on
increasing direct voltage, the voltage distribution may be still
Electrical and Electronic Insulating Materials and is the direct responsibility of
Subcommittee D09.12 on Electrical Tests.
Current edition approved March 10, 1997. Published March 1998. Originally
e1
published as D 3755 – 79. Last previous edition D 3755 – 86 (1995) .
2 4
Annual Book of ASTM Standards, Vol 10.01. Available from American National Standards Institute, 11 West 42nd St., 13th
Annual Book of ASTM Standards, Vol 10.03. Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D3755–97
largely capacitive, but depends partly on the rate of voltage 6.6 Ground Switch—The power supply shall be equipped
increase. After steady application of direct voltage the voltage with a grounding switch that is gravity operated and designed
division across the test specimen is determined by resistance. to close in less than 0.5 s. The grounding switch shall connect
The choice of direct or alternating voltage depends upon the the high-voltage output terminal of the power supply and
purpose for which the breakdown test is to be used, and to ground terminal through a low resistance when the input
some extent, on the intended application of the material. supply power is removed or the test chamber door is opened.
5.4 A more complete discussion of the significance of
7. Safety Precautions
dielectric breakdown tests is given in Appendix X1 of this
method and of Test Method D 149. Those appendix sections of
7.1 Warning— Lethal voltages are a potential hazard
Test Method D 149 that refer to alternating voltage are not during the performance of this test. It is essential that the test
applicable to the direct-voltage method.
apparatus, and all associated equipment electrically connected
to it, be properly designed and installed for safe operation.
6. Apparatus
Solidly ground all electrically conductive parts which it is
6.1 Basic Direct-Voltage Power Supplies, or dielectric test
possible for a person to contact during the test. Provide means
sets of various voltage ratings, that can operate with one of the
for use at the completion of any test to ground any parts which
two output terminals grounded, are commonly available com-
were at high voltage during the test or have the potential for
mercially. Such apparatus customarily includes the necessary
acquiring an induced charge during the test or retaining a
voltage-control, voltage-measuring, and circuitinterrupting
charge even after disconnection of the voltage source. Thor-
equipment. A provision for retaining the breakdown voltage
oughly instruct all operators as to the correct procedures for
reading after breakdown is desirable.
performing tests safely. When making high voltage tests,
6.1.1 For a direct voltage derived from a rectified and
particularly in compressed gas or in oil, it is possible for the
filtered power frequency source, ripple on the output voltage
energy released at breakdown to be suffıcient to result in fire,
generally should be less than 1 %. The criterion is met if the
explosion, or rupture of the test chamber. Design test equip-
time constant of the circuit is at least 0.4 s. The time constant
ment, test chambers, and test specimens so as to minimize the
is product of the filter capacitance plus the specimen capaci-
possibility of such occurrences and to eliminate the possibility
tance in microfarads, and the specimen insulation resistance (in
of personal injury. If the potential for fire exists, have fire
megohms) corresponding to the parallel combination of the
suppression equipment available.
voltmeter circuit resistance and the specimen resistance.
7.2 When a direct-voltage test has been applied to the test
6.2 Voltage Control, that will enable the test voltage to be
specimen, both the specimen and power supply can remain
increased at a linear rate. Preference should be given to a
charged after the test voltage source has been de-energized.
variable-speed motor-driven voltage control over a manual
This may present a hazard to test personnel. Direct-voltage
control. The rate-of-rise of test voltage shall not vary more than
testing may be more hazardous than testing with alternating
620 % from the specified rate at any point.
voltage, where the charge on the specimen is rapidly dissipated
6.3 Voltmeter, to measure the voltage directly applied to the
in the low-impedance winding of the test transformer after the
electrode system. The response of the voltmeter shall be such
test is de-energized.
that its time lag shall not introduce an error greater than 1 % of
7.3 The test specimen and high-voltage output of the power
full scale at any rate-of-rise used. The overall accuracy of the
supply must be enclosed in a grounded metallic screen. Access
voltmeter and the voltage-measuring device used shall be such
to the test enclosure must be dependent upon prior grounding
that the measurement error will not exceed 62 % of full scale
of the power supply and test specimen through a low resistance
and be in accordance with ANSI C68.1.
as referred to in 6.6.
6.4 Electrodes:
7.4 A manual grounding stick must be used to completely
6.4.1 For those cases when the insulating material is in the
discharge the test specimen and power supply after the test and
form of flat sheet or tape, or is of the nature of a semisolid (for
prior to handling them. The grounding stick should be left in
example, grease potting material, etc.) the electrodes may be
contact with the test specimen and high-voltage transformer
selected from those listed in Table 2 of Test Method D 149. The
terminals for as long as feasible.
electrode contact pressure shall be adequate to obtain good
7.5 Warning—Ozone is a physiologically hazardous gas at
electrical contact.
elevated concentrations. Levels of acceptable industrial expo-
6.4.2 Where excellent electrode contact is considered im-
sure have been established by the American Conference of
portant, use paint or vaporized metal electrodes. Such elec-
Government and Industrial Hygienists. Ozone has a distinc-
trodes may also be used when specimen geometry prevents the
tive odor that is initially discernible at low concentrations, but
use of rigid, solid metal electodes. The results obtained with
temporary loss of the sense of smell can occur. It is likely to be
painted or sprayed electrodes may not be comparable with
present wherever voltages exist that are sufficient to cause
those obtained using other types of electrodes.
partial or complete discharges in air or other atmospheres
6.5 Test Chamber—For tests under other than ambient
containing oxygen. When the odor of ozone is persistently
conditions, the specimen must be placed in a suitable environ-
present or when ozone generating conditions continue, the
mental chamber of adequate size. For tests at elevated tem-
peratures, an oven that meets the requirements of Specification
D 2436 may be convenient. The test chamber must be equipped
American Conference of Governmental Industrial Hygienists, Building D-7,
with safety devices (Section 7). 6500 Glenway Drive, Cincinnati, OH 45211.
D3755–97
concentration of ozone in the atmosphere should be measured 10. Thickness
using commercially available monitoring devices. Appropriate
10.1 The thickness used in computing the dielectric strength
means, such as installation of exhaust vents, shall be taken to
shall be the average thickness of the specimen measured as
maintain ozone concentrations in working areas within accept-
specified in the test method for the material involved. If not
able levels.
specified, the thickness measurement shall be made at room
temperature of 25 6 5°C.
8. Criteria of Breakdown
10.2 If the material is laminar or known to vary in dielectric
strength with orientation, such as caused by graininess, the
8.1 Dielectric breakdown is generally accompanied by an
specimen should be cut so that its thickness is in the direction
increase in current in the test circuit that may activate a sensing
of the electric field under use conditions.
element such as a circuit breaker, a fuse, or current-sensing
10.3 When thin materials, such as laminates, are to be tested
circuit. If sensitivity of the element is well coordinated with the
in the direction of their width or length, special procedures may
characteristics of the test equipment and the material under
be needed to avoid flashover, some of which are described in
test, its operation may be a positive indication of breakdown.
9.4. Provisions for such tests may also be included in the
8.2 Failure of a circuit breaker to operate may not be a
methods for specific materials.
positive criterion of the absence of breakdown. A breaker may
fail to trip because it is set for too great a current or because of
11. Number of Tests
malfunction. On the other hand, if the tripping circuit is set for
too low a current, currents due to leakage or partial discharge
11.1 Unless otherwise specified, test five specimens.
(corona) may cause it to trip before breakdown voltage is
reached.
12. Conditioning
8.3 Observe the specimen during the test to ascertain that
12.1 The dielectric strength of most insulating materials
tripping of the breaker or current-sensing circuit is not caused
varies with temperature and humidity. Condition such materi-
by flashover. When flashover is a problem, it will be necessary
als in a suitably controlled chamber. For information concern-
to provide for more creepage distance around the electrodes, to
ing the conditioning treatment, refer to the particular method
decrease specimen thickness, or to immerse the specimen in a
for a given material. Keep the test specimens in the chamber
liquid dielectric (Section 13).
long enough to reach a uniform temperature and humidity
8.4 Observation of actual rupture or decomposition is posi- before tests are started. It may be desirable to determine the
tive evidence of specimen breakdown. In test position, how- dielectric behavior of a material over a range of temperature
ever, these physical evidences of breakdown may not be and humidity to which it is likely to be subjected in use. If
apparent. If breakdown is in question it is common practice to conditioning is performed under conditions where condensa-
repeat the test on the same specimen. Breakdown is confirmed tion will occur, it may be desirable to wipe off the surface of
when reapplication of test voltage results in a substantially the test specimen carefully immediately before testing, as this
lower breakdown voltage. will generally tend to minimize flashover.
12.2 Since some materials require a long time to attain
equilibrium at normal conditions of temperature and humidity
9. Test Specimens
specify conditioning when specimens are to be subjected to
9.1 For a description of test specimens of materials and their
tests for
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.