ASTM D3382-95(2001)e1
(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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An American National Standard
e1
Designation:D3382–95 (Reapproved 2001)
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 D3382; 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 (e) indicates an editorial change since the last revision or reapproval.
e NOTE—The address in Footnote Four was editorially updated April 2001.
1. Scope D1868 Test Method for Detection and Measurement of
Partial Discharge (Corona) Pulses in Evaluation of Insu-
1.1 These test methods cover two bridge techniques for
lation Systems
measuring the energy and integrated charge of pulse and
pulseless partial discharges:
3. Terminology
1.2 Test Method A makes use of capacitance and loss
3.1 Definitions:
characteristics such as measured by the transformer ratio-arm
3.1.1 pseudoglow discharge, n—a type of partial discharge
bridge or the high-voltage Schering bridge (Test Methods
characterized by pulses of relatively small amplitude, and,
D150). Test Method A can be used to obtain the integrated
generally, a long rise time.
charge transfer and energy loss due to partial discharges in a
3.1.1.1 Discussion—As a result of the upper frequency
dielectric from the measured increase in capacitance and tan d
limitation in their Fourier frequency spectrum, pseudoglow
with voltage.
discharges are not readily detected by conventional partial-
1.3 Test Method B makes use of a somewhat different
discharge-pulse detectors. Pseudoglow discharges are also
bridge circuit, identified as a charge-voltage-trace (parallelo-
characterized by a diffused glow, that cannot be visually
gram) technique, which indicates directly on an oscilloscope
distinguished from that due to a true-glow discharge.
the integrated charge transfer and the magnitude of the energy
3.1.2 pulse discharge, n—a type of partial-discharge phe-
loss due to partial discharges.
nomenon characterized by a spark-type breakdown.
1.4 Both test methods are intended to supplement the
3.1.2.1 Discussion—The resultant detected pulse discharge
measurement and detection of pulse-type partial discharges as
has a short rise time and its Fourier frequency spectrum may
coveredbyTestMethodD1868,bymeasuringthesumofboth
extend as far as 100 MHz. Such a pulse discharge may be
pulse and pulseless discharges per cycle in terms of their
readily detected by conventional pulse detectors, that are
charge and energy.
generally designed for partial-discharge measurements within
1.5 This standard does not purport to address all of the
the frequency band from 30 kHz to several megahertz.
safety concerns, if any, associated with its use. It is the
3.1.3 pulseless-glow discharge, n—a type of partial-
responsibility of the user of this standard to establish appro-
discharge phenomenon characterized by a diffused glow.
priate safety and health practices and determine the applica-
3.1.3.1 Discussion—The overall voltage waveform across a
bility of regulatory limitations prior to use.Specificprecaution
gap-space undergoing a pulseless-glow discharge does not
statements are given in Section 7.
indicatethepresenceofanyabruptvoltagefalls,exceptforthe
2. Referenced Documents two at the beginning of each half cycle (for example, thyratron
behavior)(1)(2). Althoughdischargeenergyisexpendedover
2.1 ASTM Standards:
the pulseless region, a conventional partial-discharge-pulse
D150 Test Methods for AC Loss Characteristics and Per-
detector will give no indication of this as it will only respond
mittivity (Dielectric Constant) of Solid Electrical Insulat-
to the two initiating breakdowns.
ing Materials
3.1.4 See (3) and (4) for more information on the previous
D1711 Terminology Relating to Electrical Insulation
definitions.
3.1.5 For definitions of other terms pertaining to this stan-
dard refer to Terminology D1711.
These test methods are under the jurisdiction of ASTM Committee D09 on
3.2 Symbols:Symbols:
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 D3382–75. Last previous edition D3382–86(1990) . Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
Annual Book of ASTM Standards, Vol 10.01. these test methods.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D3382
3.2.1 Refer to Annex A1 for symbols for mathematical 6. Sources of Errors
terms used in this standard.
6.1 Surface Discharges—All discharges in the test speci-
men are measured, whether on the surface or in internal
4. Summary of Test Methods
cavities. If it is desired to measure only internal cavities, the
other discharges must be avoided. In the case of an insulated
4.1 The dielectric characteristics of a specimen of solid
conductor with an outer electrode on the surface (such as a
insulating material may be represented by a parallel combina-
cableorgeneratorcoil),thesurfacedischargesattheendofthis
tionofcapacitanceandconductance.Thevaluesofcapacitance
outer electrode can be removed from the measurement with a
and conductance remain practically constant over the useful
closely-spaced guard ring connected to ground. See Section 4
range of alternating voltage stress at a fixed frequency. If,
of Test Methods D150.
however, the specimen contains gaseous inclusions (cavities),
incremental increases in capacitance and conductance occur as 6.2 Since tests will be made at ionizing voltage, all connec-
tions making up the complete high-voltage circuit should be
thevoltagestressisraisedabovethevaluenecessarytoinitiate
free of corona to avoid measurement interference. See Section
partial discharges in the cavities. The energy loss in the
5 of Test Method D1868.
incremental conductance is considered to be that dissipated by
the partial discharges.
6.3 Other phenomena in addition to partial discharges may
produce anomalous changes in insulation losses with changes
4.2 In Test MethodAan initial measurement is made of the
in voltage stress. Such losses are a source of error in these
capacitance and loss characteristic of the specimen at an
methods, since they are indistinguishable from discharge
applied voltage below the discharge inception level. The
losses. However, these losses are often negligible in compari-
voltage is then raised to the specified test value and a second
son with partial discharge losses.
measurementmade.Theenergylossduetopartialdischargesis
calculated from the results of the two measurements. 6.4 Any temperature change in the specimen between the
timesatwhichthelow-voltageandhigh-voltagemeasurements
4.3 In Test Method B a special bridge circuit is balanced at
are taken may cause a change in the normal losses and appear
a voltage below the discharge inception level. The voltage is
as changes in discharge energy, thus causing an error in test
then raised to the specified test value, but the bridge is not
results. This situation can be recognized in Method B and
rebalanced.Anyunbalancedvoltageatthedetectorterminalsis
corrective action taken (see 11.3).
displayed in conjunction with the test voltage on an oscillo-
6.5 Paint used to grade potential on the surface of some
scope. The oscilloscope pattern approximates a parallelogram,
insulation specimens (for example, generator stator coil)
the area of which is a measure of the energy loss due to partial
should not be included in the measurement, since the conduc-
discharges.
tance of such paints may change with voltage and affect the
accuracy of the method as a measure of discharge energy. It is
5. Significance and Use
sometimes possible to exclude the painted surfaces from the
5.1 These test methods are useful in research and quality
measuring circuit by the use of guarding or shielding tech-
control for evaluating insulating materials and systems since
niques.
theyprovideforthemeasurementofchargetransferandenergy
loss due to partial discharges (5) (6) (7).
7. Hazards
5.2 Pulse measurements of partial discharges indicate the
7.1 Warning— Lethal voltages may be present during this
magnitude of individual discharges. However, if there are
test. It is essential that the test apparatus, and all associated
numerous discharges per cycle it may be important to know
equipment that may be electrically connected to it, be properly
their charge sum, since this sum can be related to the total
designed and installed for safe operation. Solidly ground all
volume of internal gas spaces that are discharging, if it is
electrically conductive parts that any person might come in
assumed that the gas cavities are simple capacitances in series
contact with during the test. Provide means for use at the
with the capacitances of the solid dielectrics (8).
completion of any test to ground any parts which: were at high
5.3 Internal (cavity-type) discharges may be of a glow,
voltage during the test; may have acquired an induced charge
pulseless, or pseudoglow nature, which are not indicated by
during the test; may retain a charge even after disconnection of
conventionalpulse-dischargedetectors (1) (2) (5).Pseudoglow
the voltage source. Thoroughly instruct all operators in the
discharges are detected primarily in terms of their effects upon
proper way to conduct tests safely. When making high voltage
tan d and capacitance, since their rise times are much too long
tests, particularly in compressed gas or in oil, the energy
to excite pulse detectors as covered in Test Method D1868.
released at breakdown may be suffıcient to result in fire,
5.4 Pseudoglow discharges have been observed to occur in explosion, or rupture of the test chamber. Design test equip-
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
long periods to accumulate acidic degradation products. Also
7.2 Warning— Ozone is a physiologically hazardous gas at
in some applications, like turbogenerators, where a low mo- elevated concentrations. The exposure limits are set by gov-
lecularweightsuchashydrogenorheliumisusedasacoolant,
ernmental agencies and are usually based upon recommenda-
pseudoglow discharges may develop. tions made by the American Conference of Governmental
D3382
Industrial Hygienists. Ozone is likely to be present whenever 9. Precision and Bias
voltages exist which are suffıcient to cause partial, or complete,
9.1 This test method has been in use for many years, but no
discharges in air or other atmospheres that contain oxygen.
statement for precision has been made and no activity is
Ozone has a distinctive odor which is initially discernible at
planned to develop such a statement.
low concentrations but sustained inhalation of ozone can cause
9.2 A statement of bias is not possible due to the lack of a
temporary loss of sensitivity to the scent of ozone. Because of
standard reference material.
this it is important to measure the concentration of ozone in the
10. Interferences
atmosphere, using commercially available monitoring devices,
whenever the odor of ozone is persistently present or when 10.1 Harmonics—The test voltage must be reasonably free
ozone generating conditions continue. Use appropriate means, of harmonics in order to produce the required horizontal line
such as exhaust vents, to reduce ozone concentrations to below the inception voltage. Harmonics will produce a wavy
acceptable levels in working areas. rather than a flat line. If the waviness is too severe, the voltage
source may have to be filtered to remove the harmonics. The
TEST METHOD A removalofharmonicsismoreimportantwhenthequantitiesto
be measured are small.
8. Procedure
TEST METHOD B
8.1 Conventional circuits for the measurement of
11. Procedure
alternating-voltage capacitance and loss characteristics of in-
11.1 The test method requires the placing of the test
sulationmaybeusedforthismethod.Thetransformer-ratioarm
specimen,consideredessentiallyasahigh-voltagecapacitor,in
bridge shown in Fig. 1, or the Schering bridge shown in Fig.
series with a low-voltage capacitor, across a sinusoidal test-
X4.2ofTestMethodsD150arewellsuitedtothisapplication.
voltage source. See Fig. 2. Two other bridge arms provide a
8.2 Energize the test specimen at a low voltage, V , below
voltage for balancing, at an applied voltage level below
the discharge-inception voltage, and measure capacitance C
x1
inception of partial discharges, the sinusoidal voltage across
and dissipation factor tan d . Raise the voltage to a specified
the low-voltage capacitor.Any partial discharges that occur at
test level, V , and repeat the measurements for C and tan d .
2 x2 2
higher applied voltages in the specimen will be integrated by
Calculate the power loss, DP, in watts due to discharges at
the low-voltage capacitor to produce an unbalanced voltage.
voltage V as follows:
The unbalanced voltage controls the vertical deflection of an
DP5vV @C tan d 2 C tan d ! (1)
2 x2 2 x1 1 oscilloscope beam, while a voltage proportional to, and in
2 2
phase with, the test voltage controls the horizontal deflection.
5 P 2 ~P V /V ! (2)
2 1 2 1
A description of a suitable circuit for this test method is
8.3 The increment of dissipation factor tan d −tan d ,
2 1
detailed in Annex A2.
called delta tan delta, and written D tan d, is often used as an
11.2 The oscilloscope display is simply a horizontal line
index of discharge intensity.
below the discharge inception voltage where no unbalanced
voltages occur. Above the discharge inception voltage the
displayopensintoanapproximateparallelogram.Theheightof
the parallelogram represents the sum of the partial discharges
perhalfcycle,andthearearepresentstheenergydissipatedper
1330 Kemper Meadow Drive, Suite 600, Cincinnati, OH 45200.
cycle by the discharges. See Fig. 3.
11.3 If the parallelogram has been tilted or distorted by the
increase in voltage, a small adjustment in the capacitance and
resistance balance can be made to make the top and bottom of
the parallelogram horizontal. This will compensate for some
changes in capacitance and tan d due to effects other than
partial discharges.
12. Calibration of Oscilloscope Coefficients
12.1 Inordertoevaluatetheparallelogram,itisnecessaryto
d
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