ASTM D1868-93(1998)

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An American National Standard
Designation:D1868–93(Reapproved 1998)
Standard Test Method for
Detection and Measurement of Partial Discharge (Corona)
Pulses in Evaluation of Insulation Systems
This standard is issued under the fixed designation D1868; 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.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope D149 Test Method for Dielectric Breakdown Voltage and
Dielectric Strength of Solid Electrical Insulating Materials
1.1 This test method covers the detection and measurement
at Commercial Power Frequencies
of partial discharge (corona) pulses at the terminals of an
D618 Practice for Conditioning Plastics and Electrical
insulation system under an applied test voltage, including the
Insulating Materials for Testing
determination of partial discharge (corona) inception and
D2275 Test Method for Voltage Endurance of Solid Elec-
extinction voltages as the test voltage is raised and lowered.
trical Insulating Materials Subjected to Partial Discharges
Thetestmethodisalsousefulindeterminingquantitiessuchas
(Corona) on the Surface
apparent charge and pulse repetition rate together with such
D3382 Test Methods for Measurement of Energy and
integrated quantities as average current, quadratic rate and
Integrated Charge Transfer Due to Partial Discharges
power. The test method is useful for test voltages ranging in
(Corona) Using Bridge Techniques
frequency from zero (direct voltage) to approximately 2000
2.2 Other Documents:
Hz.
AEIC CS5-87 Specifications for Thermoplastic and
1.2 The test method is directly applicable to a simple
Crosslinked Polyethylene Insulated Shielded Power
insulation system that can be represented as a two-terminal
Cables Rated 5 through 35 kV (9th Edition) October
capacitor (1), (2).
1.3 Thetestmethodisalsoapplicableto(distributedparam-
ICEA T-24-380 Guide for Partial Discharge Procedure
eter) insulation systems such as high-voltage cable. Consider-
IEEE 48 Standard Test Procedures and Requirements for
ationmustbegiventoattenuationandreflectionphenomenain
High Voltage Alternating Current Cable Terminations
this type of system. Further information on distributed param-
eter systems will be found in Refs. (1), (2), (3), and (4).
3. Terminology
1.4 The test method can be applied to multi-terminal insu-
3.1 Definitions—The following terms are presented in a
lation systems, but at some loss in accuracy, especially where
developing sequence; it is best that they be read in their
the insulation of inductive windings is involved.
entirety:
1.5 This standard does not purport to address all of the
3.1.1 ionization—the process by which electrons are lost
safety problems, if any, associated with its use. It is the
from or transferred to neutral molecules or atoms to form
responsibility of the user of this standard to establish appro-
positively or negatively charged particles.
priate safety and health practices and determine the applica-
3.1.2 partial discharge (corona)—an electrical discharge
bility of regulatory limitations prior to use.Specificprecaution
thatonlypartiallybridgestheinsulationbetweenconductors.A
statements are given in Sections 8 and 14.
transient gaseous ionization occurs in an insulation system if
2. Referenced Documents
2.1 ASTM Standards:
Annual Book of ASTM Standards, Vol 10.01.
Annual Book of ASTM Standards, Vols 08.01 and 10.01.
Annual Book of ASTM Standards, Vol 10.02.
1 6
This test method is under the jurisdiction of ASTM Committee D-9 on Available from the publication department of the Association of Edison
Electrical and Electronic Insulating Materials and is the direct responsibility of Illuminating Companies, 600 N. 18th St., PO Box 2641, Birmingham, AL
Subcommittee D09.12 on Electrical Tests. 35291-0992.
Current edition approved June 15, 1993. Published August 1993. Originally Available from the Insulated Cable Engineers Association, Inc., PO Box 440,
e1
published as D1868–61 T. Last previous edition D1868–81(1990) . South Yarmouth, MA 02664.
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof Available from the Institute of Electrical and Electronics Engineers Service
this test method. Center, 445 Hoes Lane, Piscataway, NJ 08854.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D1868
the voltage stress exceeds a critical value, and this ionization 3.1.10 average discharge (corona) current (I)—the sum of
t
produces partial discharges. the absolute magnitudes of the individual discharges during a
certain time interval divided by that time interval. When the
3.1.3 corona—visiblepartialdischargesingasesadjacentto
a conductor. This term has also been used to refer to partial discharges are measured in coulombs and the time interval in
seconds, the calculated current will be in amperes.
discharges in general.
3.1.4 continuous partial discharges (continuous corona)— t
Q 1 Q 1222222 Q
(
dischargesthatrecuratratherregularintervals;forexampleon 1 2 n
t
I 5 (2)
approximately every cycle of an alternating voltage or at least t
t 2 t
1 0
once per minute for an applied direct voltage.
where:
3.1.5 partial discharge (corona) inception voltage (PDIV
I 5 average current, A,
t
[CIV])—the lowest voltage at which continuous partial dis-
t 5 starting time, s,
charges above some stated magnitude (which may define the
t 5 completion time, s, and
limit of permissible background noise) occur as the applied
Q,Q,Q 5 partialdischargequantityinacoronapulse1
1 2 n
voltage is gradually increased (Note 1). Where the applied
through n, C.
voltage is alternating, the PDIV is expressed as 1/=2ofthe
3.1.11 quadratic rate—the sum of the squares of the indi-
peak voltage. Many test and specimen parameters can affect
vidual discharge magnitudes during a certain time interval
thisvalue,andinsomecasesreproducibilitymaybedifficultto
dividedbythattimeinterval.Thequadraticrateisexpressedas
achieve.
(coulombs) per second.
NOTE 1—ManyfactorsmayinfluencethevalueofthePDIVandPDEV
3.1.12 partial discharge (corona) energy (W)— the energy
includingtherateatwhichthevoltageisincreasedordecreasedaswellas
drawnfromthetestvoltagesourceastheresultofanindividual
theprevioushistoryofthevoltageappliedtothespecimen.Inmanycases
discharge.ItistheproductofthemagnitudeQofthatdischarge
it may be difficult to obtain the same value with subsequent tests.
and the instantaneous value V of the voltage across the test
Moreover, the “continuous” character of the partial discharges is
sometimes quite difficult to define, and an arbitrary judgment in this specimen at the inception of the discharge (5). Thus the
respect may lead to different values of the PDIV or PDEV.
discharge energy of the ith pulse is:
3.1.6 partial discharge (corona) extinction voltage (PDEV W 5 QV (3)
i i i
[CEV])—the highest voltage at which partial discharges above
where:
some stated magnitude no longer occur as the applied voltage
W 5 the discharge energy, W·s( 5J),
i
is gradually decreased from above the inception voltage (see
Q 5 the partial discharge magnitude, (see 3.1.8), and
i
Note 1).Where the applied voltage is alternating, the PDEVis
V 5 the instantaneous value of the applied test voltage at
i
expressed as 1/ 2 of the peak voltage. Many test and
=
the time of the discharge, V.
specimen parameters can affect this value, and in some cases
3.1.13 partial discharge (corona) power loss (P)— the
reproducibility may be difficult to achieve.
summation of the energies drawn from the test voltage source
3.1.7 partial discharge pulse voltage (V)—the terminal
t
by individual discharges occurring over a period of time,
pulse voltage resulting from a partial discharge represented as
divided by that time period.
a voltage source suddenly applied in series with the capaci-
i 5 m
tance of the insulation system under test, and that would be
P 5 QV (4)
(
i i
T
detected at the terminals of the system under open-circuit
i 51
conditions.
where:
3.1.8 partial discharge quantity (terminal corona charge)
P 5 the discharge power, W,
(Q)—themagnitudeofanindividualdischargeinaninsulation
t
T 5 the time period, s,
system expressed in terms of the charge transfer measured at
m 5 the number of the final pulse during T, and
the system terminals. The measured charge is in general not
QV 5 the discharge energy of the ith pulse (see 3.1.12).
i i
equal to the charge transferred at the discharge site, and does
When pulse height analysis is used, the summation over a
have a relation to the discharge energy. For a small specimen
period of time of pulses above a preset level of corona usually
that can be treated as a simple lumped capacitor, it is equal to
determined by background noise multiplied by the instanta-
the product of the capacitance of the insulation system and the
neous test voltage at the time of the pulses in the specimen is
partial discharge pulse voltage, that is:
approximately equal to:
Q 5 CV (1)
t t t
i
P 5 nQ V (5)
(
j tj j
where:
j 51
Q 5 partial discharge quantity, C,
t
where:
C 5 capacitanceofthespecimeninsulationsystem,F,and
t
P 5 pulse discharge power loss, W,
V 5 peak value of the partial discharge pulse voltage
t
n 5 recurrence rate of the jth discharge pulse in pulses/
appearing across C,V. j
t
second.
3.1.9 partial discharge (corona) level—the magnitude of
Q 5 the corresponding value of the partial discharge
tj
the greatest recurrent discharge during an observation of
quantity in coulombs for the particular pulse.
continuous discharges.
D1868
stop in a nonuniform and unpredictable fashion, especially for
V 5 instantaneous value of the applied voltage in volts at
j
discharges within cavities in certain materials.
which the jth discharge pulse takes place (6).
5.4 Themagnitude(pulseheight)ofapartialdischargeisan
Iftheassumption(7)ismadethat V DC .C DV (where DC
j j t j j
indication of the amount of energy that it dissipates in the
is incremental capacitance rise in C due to the drop DV in V
t j j
insulation system. Partial discharge magnitude and pulse rate
asaresultofthe jthdischarge),thentheabovesummationmust
1 are useful in estimating the rate, or change of rate, at which
be multiplied by ⁄2. However, this assumption is not usually
deterioration is produced.
borne out in practice.
5.5 In general, the occurrence of partial discharges is not
3.1.14 partial discharge apparent power loss (P )—the
a
directly related to the basic properties of a solid insulating
summationoveraperiodoftimeofallcoronapulseamplitudes
material, but usually results from overstressing of gaseous
multiplied by the rms test voltage.
occlusions or similar imperfections or discontinuities in an
P 5 IV (6)
a t s
insulatingsystem.Partialdischargesmayoriginateatlocations
such as on the leads or terminals without resulting in any
where:
hazard within the main part of the insulation system.
P 5 apparent power loss in time interval (t −t ), W,
a 1 0
I 5 average corona current, A, and
t
V 5 applied rms test voltage, V.
6. Interference
s
3.1.15 partial discharge (corona) pulse rate (n)— the aver-
6.1 Radiated or conducted electrical disturbances from
age number of discharge pulses that occur per second or in
sources other than the test specimen may interfere with the
some other specified time interval. The pulse count may be
measurement of partial discharges. The magnitude of distur-
restricted to pulses above a preset threshold magnitude, or to
bances reaching the measuring instrument must be kept small
those between stated lower and upper magnitude limits.
relative to the most sensitive measurements to be made.
3.1.16 partial discharge pulse—a voltage or current pulse
6.2 Interferencefromradiationmaybereducedbyshielding
that occurs at some designated location in a circuit as a result
the test circuit or by conducting the test in a shielded room.
of a partial discharge.
Interference by conduction may be suppressed by means of a
low-pass filter in the voltage supply circuit.
4. Summary of Test Method
6.3 Coronaontheconnectingleadsbetweenthetestvoltage
4.1 A specimen insulation system is energized in a test source and the specimen may interfere with the measurement.
circuitbyahigh-voltagesource.Apartialdischarge(corona)in Such interference may be avoided if the leads are smooth-
the specimen will cause a sudden charge transfer and a surfaced and of sufficient diameter, with spherical terminals.
resulting voltage pulse at the specimen terminals.Ameasuring 6.4 Interference may often be identified from the display of
instrument coupled to the terminals may be calibrated to
an oscilloscope coupled to the measuring circuit, with its
respond to the voltage pulse in terms of the charge transferred horizontal deflection relating to the instantaneous value of the
at the terminals.
test voltage. For example, pulses that appear only during the
negative half-cycle of the alternating test voltage are often the
5. Significance and Use result of corona originating on the connecting lead or terminal
ratherthantheresultofpartialdischargeswithinthespecimen.
5.1 The presence of partial discharges (corona) at operating
6.5 Interference may be controlled by the use of time
voltage in an insulation system may result in a significant
window circuits that suppress the measuring device input
reduction in the life of the insulating material. Some materials
during the portion of the test voltage wave when partial
are more susceptible to such discharge damage than others.
discharges do not occur, that is, at the voltage zero-crossing
This characteristic can be investigated using Test Method
points. Using this technique take care to avoid the loss of
D2275 (6).
wanted signals. Other more sophisticated interference suppres-
5.2 The presence of partial discharges (corona) in an appar-
sion techniques of signal processing can be used (1).
ently solid insulation may be an indication of the existence of
internal cavities. Partial discharge tests have been useful in the
7. Apparatus
design and inspection of molded, laminated, and composite
insulation, as well as specimens in the form of cables, 7.1 Test Voltage Supply:
capacitors, transformers, and bushings.
7.1.1 The voltage supply must be capable of energizing the
5.3 Partial discharge (corona) inception and extinction volt- test circuit, including the specimen, over a range of voltages to
ages are used in the determination of the limiting voltage at the maximum desired test value.
...