ASTM D3382-95
(Test Method)Standard Test Methods for Measurement of Energy and Integrated Charge Transfer Due to Partial Discharges (Corona) Using Bridge Techniques
Standard Test Methods for Measurement of Energy and Integrated Charge Transfer Due to Partial Discharges (Corona) Using Bridge Techniques
SCOPE
1.1 These test methods cover two bridge techniques for measuring the energy and integrated charge of pulse and pulseless partial discharges:
1.2 Test Method A makes use of capacitance and loss characteristics such as measured by the transformer ratio-arm bridge or the high-voltage Schering bridge (Test Methods D150). Test Method A can be used to obtain the integrated charge transfer and energy loss due to partial discharges in a dielectric from the measured increase in capacitance and tan [delta] with voltage.
1.3 Test Method B makes use of a somewhat different bridge circuit, identified as a charge-voltage-trace (parallelogram) technique, which indicates directly on an oscilloscope the integrated charge transfer and the magnitude of the energy loss due to partial discharges.
1.4 Both test methods are intended to supplement the measurement and detection of pulse-type partial discharges as covered by Test Method D1868, by measuring the sum of both pulse and pulseless discharges per cycle in terms of their charge and energy.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific precaution statements are given in Section 7.
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Designation: D 3382 – 95 An American National Standard
Standard Test Methods for
Measurement of Energy and Integrated Charge Transfer Due
to Partial Discharges (Corona) Using Bridge Techniques
This standard is issued under the fixed designation D 3382; 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 3. Terminology
1.1 These test methods cover two bridge techniques for 3.1 Definitions:
measuring the energy and integrated charge of pulse and 3.1.1 pseudoglow discharge, n—a type of partial discharge
pulseless partial discharges: characterized by pulses of relatively small amplitude, and,
1.2 Test Method A makes use of capacitance and loss generally, a long rise time.
characteristics such as measured by the transformer ratio-arm 3.1.1.1 Discussion—As a result of the upper frequency
bridge or the high-voltage Schering bridge (Test Methods limitation in their Fourier frequency spectrum, pseudoglow
D 150). Test Method A can be used to obtain the integrated discharges are not readily detected by conventional partial-
charge transfer and energy loss due to partial discharges in a discharge-pulse detectors. Pseudoglow discharges are also
dielectric from the measured increase in capacitance and tan d characterized by a diffused glow, that cannot be visually
with voltage. distinguished from that due to a true-glow discharge.
1.3 Test Method B makes use of a somewhat different 3.1.2 pulse discharge, n—a type of partial-discharge phe-
bridge circuit, identified as a charge-voltage-trace (parallelo- nomenon characterized by a spark-type breakdown.
gram) technique, which indicates directly on an oscilloscope 3.1.2.1 Discussion—The resultant detected pulse discharge
the integrated charge transfer and the magnitude of the energy has a short rise time and its Fourier frequency spectrum may
loss due to partial discharges. extend as far as 100 MHz. Such a pulse discharge may be
1.4 Both test methods are intended to supplement the readily detected by conventional pulse detectors, that are
measurement and detection of pulse-type partial discharges as generally designed for partial-discharge measurements within
covered by Test Method D 1868, by measuring the sum of both the frequency band from 30 kHz to several megahertz.
pulse and pulseless discharges per cycle in terms of their 3.1.3 pulseless-glow discharge, n—a type of partial-
charge and energy. discharge phenomenon characterized by a diffused glow.
1.5 This standard does not purport to address all of the 3.1.3.1 Discussion—The overall voltage waveform across a
safety concerns, if any, associated with its use. It is the gap-space undergoing a pulseless-glow discharge does not
responsibility of the user of this standard to establish appro- indicate the presence of any abrupt voltage falls, except for the
priate safety and health practices and determine the applica- two at the beginning of each half cycle (for example, thyratron
bility of regulatory limitations prior to use. Specific precaution behavior) (1) (2). Although discharge energy is expended over
statements are given in Section 7. the pulseless region, a conventional partial-discharge-pulse
detector will give no indication of this as it will only respond
2. Referenced Documents
to the two initiating breakdowns.
2.1 ASTM Standards:
3.1.4 See (3) and (4) for more information on the previous
D 150 Test Methods for AC Loss Characteristics and Per- definitions.
mittivity (Dielectric Constant) of Solid Electrical Insulat-
3.1.5 For definitions of other terms pertaining to this stan-
ing Materials dard refer to Terminology D 1711.
D 1711 Terminology Relating to Electrical Insulation
3.2 Symbols:Symbols:
D 1868 Test Method for Detection and Measurement of 3.2.1 Refer to Annex A1 for symbols for mathematical
Partial Discharge (Corona) Pulses in Evaluation of Insu-
terms used in this standard.
lation Systems
4. Summary of Test Methods
4.1 The dielectric characteristics of a specimen of solid
insulating material may be represented by a parallel combina-
These test methods are under the jurisdiction of ASTM Committee D-9 on
tion of capacitance and conductance. The values of capacitance
Electrical and Electronic Insulating Materials and are the direct responsibility of
Subcommittee D09.12 on Electrical Tests.
Current edition approved Sept. 10, 1995. Published January 1996. Originally
e1 3
published as D 3382 – 75. Last previous edition D 3382 – 86 (1990) . The boldface numbers in parentheses refer to the list of references at the end of
Annual Book of ASTM Standards, Vol 10.01. these test methods.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 3382
and conductance remain practically constant over the useful of Test Methods D 150.
range of alternating voltage stress at a fixed frequency. If, 6.2 Since tests will be made at ionizing voltage, all connec-
however, the specimen contains gaseous inclusions (cavities), tions making up the complete high-voltage circuit should be
incremental increases in capacitance and conductance occur as free of corona to avoid measurement interference. See Section
the voltage stress is raised above the value necessary to initiate 5 of Test Method D 1868.
partial discharges in the cavities. The energy loss in the 6.3 Other phenomena in addition to partial discharges may
incremental conductance is considered to be that dissipated by produce anomalous changes in insulation losses with changes
the partial discharges. in voltage stress. Such losses are a source of error in these
4.2 In Test Method A an initial measurement is made of the methods, since they are indistinguishable from discharge
capacitance and loss characteristic of the specimen at an losses. However, these losses are often negligible in compari-
applied voltage below the discharge inception level. The son with partial discharge losses.
voltage is then raised to the specified test value and a second 6.4 Any temperature change in the specimen between the
measurement made. The energy loss due to partial discharges is times at which the low-voltage and high-voltage measurements
calculated from the results of the two measurements. are taken may cause a change in the normal losses and appear
4.3 In Test Method B a special bridge circuit is balanced at as changes in discharge energy, thus causing an error in test
a voltage below the discharge inception level. The voltage is results. This situation can be recognized in Method B and
then raised to the specified test value, but the bridge is not corrective action taken (see 11.3).
rebalanced. Any unbalanced voltage at the detector terminals is 6.5 Paint used to grade potential on the surface of some
displayed in conjunction with the test voltage on an oscillo- insulation specimens (for example, generator stator coil)
scope. The oscilloscope pattern approximates a parallelogram, should not be included in the measurement, since the conduc-
the area of which is a measure of the energy loss due to partial tance of such paints may change with voltage and affect the
discharges. accuracy of the method as a measure of discharge energy. It is
sometimes possible to exclude the painted surfaces from the
5. Significance and Use
measuring circuit by the use of guarding or shielding tech-
5.1 These test methods are useful in research and quality
niques.
control for evaluating insulating materials and systems since
7. Hazards
they provide for the measurement of charge transfer and energy
loss due to partial discharges (5) (6) (7).
7.1 Warning— Lethal voltages may be present during this
5.2 Pulse measurements of partial discharges indicate the
test. It is essential that the test apparatus, and all associated
magnitude of individual discharges. However, if there are
equipment that may be electrically connected to it, be properly
numerous discharges per cycle it may be important to know
designed and installed for safe operation. Solidly ground all
their charge sum, since this sum can be related to the total
electrically conductive parts that any person might come in
volume of internal gas spaces that are discharging, if it is
contact with during the test. Provide means for use at the
assumed that the gas cavities are simple capacitances in series
completion of any test to ground any parts which: were at high
with the capacitances of the solid dielectrics (8).
voltage during the test; may have acquired an induced charge
5.3 Internal (cavity-type) discharges may be of a glow,
during the test; may retain a charge even after disconnection of
pulseless, or pseudoglow nature, which are not indicated by
the voltage source. Thoroughly instruct all operators in the
conventional pulse-discharge detectors (1) (2) (5). Pseudoglow
proper way to conduct tests safely. When making high voltage
discharges are detected primarily in terms of their effects upon
tests, particularly in compressed gas or in oil, the energy
tan d and capacitance, since their rise times are much too long
released at breakdown may be suffıcient to result in fire,
to excite pulse detectors as covered in Test Method D 1868. explosion, or rupture of the test chamber. Design test equip-
5.4 Pseudoglow discharges have been observed to occur in
ment, test chambers, and test specimens so as to minimize the
air, particularly when a partially conducting surface is in- possibility of such occurrences and to eliminate the possibility
volved. Such partially conducting surfaces may develop with
of personal injury.
polymers that are exposed to partial discharges for sufficiently 7.2 Warning— Ozone is a physiologically hazardous gas at
long periods to accumulate acidic degradation products. Also
elevated concentrations. The exposure limits are set by gov-
in some applications, like turbogenerators, where a low mo- ernmental agencies and are usually based upon recommenda-
lecular weight such as hydrogen or helium is used as a coolant,
tions made by the American Conference of Governmental
pseudoglow discharges may develop.
Industrial Hygienists. Ozone is likely to be present whenever
voltages exist which are suffıcient to cause partial, or complete,
6. Sources of Errors
discharges in air or other atmospheres that contain oxygen.
6.1 Surface Discharges—All discharges in the test speci-
Ozone has a distinctive odor which is initially discernible at
men are measured, whether on the surface or in internal
low concentrations but sustained inhalation of ozone can cause
cavities. If it is desired to measure only internal cavities, the
temporary loss of sensitivity to the scent of ozone. Because of
other discharges must be avoided. In the case of an insulated
this it is important to measure the concentration of ozone in the
conductor with an outer electrode on the surface (such as a
atmosphere, using commercially available monitoring devices,
cable or generator coil), the surface discharges at the end of this
outer electrode can be removed from the measurement with a
closely-spaced guard ring connected to ground. See Section 4 Building D-7, 8500 Glenway Drive, Cincinnati, OH 45211.
D 3382
whenever the odor of ozone is persistently present or when removal of harmonics is more important when the quantities to
ozone generating conditions continue. Use appropriate means, be measured are small.
such as exhaust vents, to reduce ozone concentrations to
TEST METHOD B
acceptable levels in working areas.
11. Procedure
TEST METHOD A
11.1 The test method requires the placing of the test
specimen, considered essentially as a high-voltage capacitor, in
8. Procedure
series with a low-voltage capacitor, across a sinusoidal test-
8.1 Conventional circuits for the measurement of
voltage source. See Fig. 2. Two other bridge arms provide a
alternating-voltage capacitance and loss characteristics of in-
voltage for balancing, at an applied voltage level below
sulation may be used for this method. The transformer-ratioarm
inception of partial discharges, the sinusoidal voltage across
bridge shown in Fig. 1, or the Schering bridge shown in Fig.
the low-voltage capacitor. Any partial discharges that occur at
X4.2 of Test Methods D 150 are well suited to this application.
higher applied voltages in the specimen will be integrated by
8.2 Energize the test specimen at a low voltage, V , below
the low-voltage capacitor to produce an unbalanced voltage.
the discharge-inception voltage, and measure capacitance C
x1
The unbalanced voltage controls the vertical deflection of an
and dissipation factor tan d . Raise the voltage to a specified
oscilloscope beam, while a voltage proportional to, and in
test level, V , and repeat the measurements for C and tan d .
2 x2 2
phase with, the test voltage controls the horizontal deflection.
Calculate the power loss, DP, in watts due to discharges at
A description of a suitable circuit for this test method is
voltage V as follows:
detailed in Annex A2.
11.2 The oscilloscope display is simply a horizontal line
DP5vV @C tan d 2 C tan d ! (1)
2 x2 2 x1 1
below the discharge inception voltage where no unbalanced
2 2
5 P 2 ~P V /V ! (2)
2 1 2 1
voltages occur. Above the discharge inception voltage the
8.3 The increment of dissipation factor tan d − tan d ,
2 1
display opens into an approximate parallelogram. The height of
called delta tan delta, and written D tan d, is often used as an
the parallelogram represents the sum of the partial discharges
index of discharge intensity.
per half cycle, and the area represents the energy dissipated per
cycle by the discharges. See Fig. 3.
9. Precision and Bias
11.3 If the parallelogram has been tilted or distorted by the
9.1 This test method has been in use for many years, but no
increase in voltage, a small adjustment in the capacitance and
statement for precision has been made and no activity is
resistance balance can be made to make the top and bottom of
planned to develop such a statement.
the parallelogram horizontal. This will compensate for some
9.2 A statement of bias is not possible due to the lack of a
changes in capacitance and tan d due to effects other than
standard reference material.
partial discharges.
12. Calibration of Oscilloscope Coefficients
10. Interferences
12.1 In order to evaluate the parallelogram, it is necessary to
10.1 Harmonics—The test voltage must be reasonably free
determine the deflection sensitivities of the oscilloscope. See
of harmonics in order to produce the required horizontal line
Fig. 3. The horizontal-deflection
...
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