# ASTM D1868-13

Designation: D1868 − 13Standard Test Method forDetection and Measurement of Partial Discharge (Corona)Pulses in Evaluation of Insulation Systems1This standard is issued under the fixed designation D1868; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (´) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope*1.1 This test method covers the detection and measurementof partial discharge (corona) pulses at the terminals of aninsulation system under an applied test voltage, including thedetermination of partial discharge (corona) inception andextinction voltages as the test voltage is raised and lowered.The test method is also useful in determining quantities such asapparent charge and pulse repetition rate together with suchintegrated quantities as average current, quadratic rate andpower. The test method is useful for test voltages ranging infrequency from zero (direct voltage) to approximately 2000Hz.1.2 The test method is directly applicable to a simpleinsulation system that can be represented as a two-terminalcapacitor (1), (2) .1.3 The test method is also applicable to (distributed param-eter) insulation systems such as high-voltage cable. Consider-ation must be given to attenuation and reflection phenomena inthis type of system. Further information on distributed param-eter systems of cables, transformers, and rotating machines willbe found in Refs. (1), (2), (3), (4), (5), (6), (7), (8), and (9).2(SeeAEIC CS5-87, IEEE C57 113-1991, IEEE C57 124-1991,and IEEE 1434-2005.)1.4 The test method can be applied to multi-terminal insu-lation systems, but at some loss in accuracy, especially wherethe insulation of inductive windings is involved.1.5 This standard does not purport to address all of thesafety problems, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. Specific precautionstatements are given in Sections 8 and 14.2. Referenced Documents2.1 ASTM Standards:3D149 Test Method for Dielectric Breakdown Voltage andDielectric Strength of Solid Electrical Insulating Materialsat Commercial Power FrequenciesD618 Practice for Conditioning Plastics for TestingD2275 Test Method for Voltage Endurance of Solid Electri-cal Insulating Materials Subjected to Partial Discharges(Corona) on the SurfaceD3382 Test Methods for Measurement of Energy and Inte-grated Charge Transfer Due to Partial Discharges (Co-rona) Using Bridge Techniques2.2 Other Documents:AEIC CS5-87 Specifications for Thermoplastic and Cross-linked Polyethlene Insulated Shielded Power CablesRated 5 through 35 kV (9thEdition) October 19874ICEA T-24-380 Guide for Partial Discharge Procedure5IEEE 48 Standard Test Procedures and Requirements forHigh Voltage Alternating Current Cable Terminations6IEEE 1434-2005 Guide to the Measurement of Partial Dis-charges in Rotating Machinery6IEEE C57 113-1991 Guide for PD Measurement in Liquid-Filled Power Transformers and Shunt Reactors6IEEE C57 124-1991 Recommended Practice for the Detec-tion of PD and the Measurement of Apparent Charge inDry-Type Transformers63. Terminology3.1 Definitions:1This test method is under the jurisdiction of ASTM Committee D09 onElectrical and Electronic Insulating Materials and is the direct responsibility ofSubcommittee D09.12 on Electrical Tests.Current edition approved Nov. 1, 2013. Published December 2013. Originallyapproved in 1961. Last previous edition approved in 2007 as D1868 – 07. DOI:10.1520/D1868-13.2The boldface numbers in parentheses refer to the list of references at the end ofthis test method.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at service@astm.org. For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.4Available from the publication department of the Association of EdisonIlluminating Companies, 600 N. 18th St., PO Box 2641, Birmingham, AL35291-0992.5Available from the Insulated Cable Engineers Association, Inc., PO Box 440,South Yarmouth, MA 02664.6Available from Institute of Electrical and Electronics Engineers, Inc. (IEEE),445 Hoes Ln., P.O. Box 1331, Piscataway, NJ 08854-1331, http://www.ieee.org.*A Summary of Changes section appears at the end of this standardCopyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.1 The following terms are presented in a developingsequence; it is best that they be read in their entirety:3.1.2 ionization—the process by which electrons are lostfrom or transferred to neutral molecules or atoms to formpositively or negatively charged particles.3.1.3 partial discharge (corona)—an electrical dischargethat only partially bridges the insulation between conductors.This electrical discharge, which is governed by the transientgaseous ionization process, can assume the form of either aspark characterized by a narrow discharge channel or a diffusedglow having an expanded or substantially broadened dischargechannel. The partial discharges occur in gas filled cavitiesoccluded within insulating systems and are initiated wheneverthe voltage across the cavities changes by a value equal to theirbreakdown voltage (5).3.1.4 corona—visible partial discharges in gases adjacent toa conductor. This term has also been used to refer to partialdischarges in general.3.1.5 continuous partial discharges (continuous corona)—discharges that recur at rather regular intervals; for example onapproximately every cycle of an alternating voltage or at leastonce per minute for an applied direct voltage.3.1.6 partial discharge (corona) inception voltage (PDIV[CIV])—the lowest voltage at which continuous partial dis-charges above some stated magnitude (which may define thelimit of permissible background noise) occur as the appliedvoltage is gradually increased (Note 1). Where the appliedvoltage is alternating, the PDIV is expressed as 1/√2 of thepeak voltage. Many test and specimen parameters can affectthis value, and in some cases reproducibility may be difficult toachieve.NOTE 1—Many factors may influence the value of the PDIV and PDEVincluding the rate at which the voltage is increased or decreased as well asthe previous history of the voltage applied to the specimen. In many casesit may be difficult to obtain the same value with subsequent tests.Moreover, the “continuous” character of the partial discharges issometimes quite difficult to define, and an arbitrary judgment in thisrespect may lead to different values of the PDIV or PDEV.3.1.7 partial discharge (corona) extinction voltage (PDEV[CEV])—the highest voltage at which partial discharges abovesome stated magnitude no longer occur as the applied voltageis gradually decreased from above the inception voltage (seeNote 1). Where the applied voltage is alternating, the PDEV isexpressed as 1/=2 of the peak voltage. Many test andspecimen parameters can affect this value, and in some casesreproducibility may be difficult to achieve.3.1.8 partial discharge pulse voltage (Vt)—the terminalpulse voltage resulting from a partial discharge represented asa voltage source suddenly applied in series with the capaci-tance of the insulation system under test, and that would bedetected at the terminals of the system under open-circuitconditions. The shape, rise time, and magnitude of the voltageVtof the partial discharge pulse are dependent upon thegeometry of the cavity, its size, nature of its boundaries, thetype of gas and the pressure within as well as the parameters ofthe transmission medium between the discharge site and thepartial discharge pulse detector. The partial discharge pulses ofthe spark-type discharge will have substantially shorter risetimes than those of the glow-type (10).3.1.9 partial discharge quantity (terminal corona charge)(Qt)—the magnitude of an individual discharge in an insulationsystem expressed in terms of the charge transfer measured atthe system terminals. The measured charge is in general notequal to the charge transferred at the discharge site, and doeshave a relation to the discharge energy. For a small specimenthat can be treated as a simple lumped capacitor, it is equal tothe product of the capacitance of the insulation system and thepartial discharge pulse voltage, that is:Qt5 CtVt(1)where:Qt= partial discharge quantity, C,Ct= capacitance of the specimen insulation system, F, andVt= peak value of the partial discharge pulse voltageappearing across Ct,V.3.1.10 partial discharge (corona) level—the magnitude ofthe greatest recurrent discharge during an observation ofcontinuous discharges.3.1.11 average discharge (corona) current (It)—the sum ofthe absolute magnitudes of the individual discharges during acertain time interval divided by that time interval. When thedischarges are measured in coulombs and the time interval inseconds, the calculated current will be in amperes.It5(t0t1Q11Q21222222Qnt12 t0(2)where:It= average current, A,t0= starting time, s,t1= completion time, s, andQ1,Q2,Qn= partial discharge quantity in a corona pulse 1through n, C.3.1.12 quadratic rate—the sum of the squares of the indi-vidual discharge magnitudes during a certain time intervaldivided by that time interval. The quadratic rate is expressed as(coulombs)2per second.3.1.13 partial discharge (corona) energy (W)— the energydrawn from the test voltage source as the result of an individualdischarge. It is the product of the magnitude Q of that dischargeand the instantaneous value V of the voltage across the testspecimen at the inception of the discharge (11). Thus thedischarge energy of the ith pulse is:Wi5 QiVi(3)where:Wi= the discharge energy, W·s( = J),QI= the partial discharge magnitude, (see 3.1.9), andD1868 − 132Vi= the instantaneous value of the applied test voltage at thetime of the discharge, V.3.1.14 partial discharge (corona) power loss (P)— thesummation of the energies drawn from the test voltage sourceby individual discharges occurring over a period of time,divided by that time period.P 51T(i51i5mQiVi(4)where:P = the discharge power, W,T = the time period, s,m = the number of the final pulse during T, andQiVi= the discharge energy of the ith pulse (see 3.1.13).When partial discharge pulse-height analysis is performedover a one-second interval, then the power dissapated, P, can bedetermined from:P 5(j51injQjVj(5)where:P = pulse discharge power loss, W,nj= recurrence rate of the jth discharge pulse in pulses/second.Qj= the corresponding value of the partial discharge quan-tity in coulombs for the particular pulse.Vj= instantaneous value of the applied voltage in volts atwhich the jth discharge pulse takes place (6).If the assumption (12) is made that Vj∆Cj. Ct∆Vj(where∆Cjis incremental capacitance rise in Ctdue to the drop ∆VjinVjas a result of the jth discharge), then the above summationmust be multiplied by1⁄2 . However, this assumption is notusually borne out in practice.3.1.15 partial discharge apparent power loss (Pa)—thesummation over a period of time of all corona pulse amplitudesmultiplied by the rms test voltage.Pa5 ItVs(6)where:Pa= apparent power loss in time interval (t1−t0), W,It= average corona current, A, andVs= applied rms test voltage, V.3.1.16 partial discharge (corona) pulse rate (n)—the aver-age number of discharge pulses that occur per second or insome other specified time interval. The pulse count may berestricted to pulses above a preset threshold magnitude, or tothose between stated lower and upper magnitude limits.3.1.17 partial discharge pulse—a voltage or current pulsethat occurs at some designated location in a circuit as a resultof a partial discharge.4. Summary of Test Method4.1 A specimen insulation system is energized in a testcircuit by a high-voltage source.Apartial discharge (corona) inthe specimen will cause a sudden charge transfer and aresulting voltage pulse at the specimen terminals. Calibrate ameasuring instrument coupled to the terminals to respond tothe voltage pulse in terms of the charge transferred at theterminals.5. Significance and Use5.1 The presence of partial discharges (corona) at operatingvoltage in an insulation system has the potential to result in asignificant reduction in the life of the insulating material. Somematerials are more susceptible to such discharge damage thanothers. This characteristic can be investigated using TestMethod D2275.5.2 The presence of partial discharges (corona) in an appar-ently solid insulation is a potential indication of the existenceof internal cavities. Partial discharge tests have been useful inthe design and inspection of molded, laminated, and compositeinsulation, as well as specimens in the form of cables,capacitors, transformers, bushings, stator bars, and rotatingmachines (1), (2), (3), (4), (5), (6), (7), (8), (9), (13), and (12).(See also AEIC CS5-87, ICEA T-24-380, IEEE 48, IEEE C57113-1991, IEEE C57 124-1991, and IEEE 1434-2005.)5.3 Partial discharge (corona) inception and extinction volt-ages are used in the determination of the limiting voltage atwhich an insulation system will operate free of such dis-charges. The extinction voltage is often substantially lowerthan the inception voltage. Where the operating voltage isbelow the inception voltage but above the extinction voltage, itis possible that a transient over-voltage will initiate dischargeswhich then continue until the voltage is lowered below theextinction voltage. Inception and extinction voltages dependupon many factors, including temperature and the rate at whichthe voltage is changed. After a time at a voltage, it is possiblethat discharges will start and stop in a nonuniform andunpredictable fashion, especially for discharges within cavitiesin certain materials, in particular if the discharge degradationproducts formed are conductive (1), (5).5.4 The magnitude (pulse height) of a partial discharge is anindication of the amount of energy that it dissipates in theinsulation system. Partial discharge magnitude and pulse rateare useful in estimating the rate, or change of rate, at whichdeterioration is produced.5.5 In general, the occurrence of partial discharges is notdirectly related to the basic properties of a solid insulatingmaterial, but usually results from overstressing of gaseousocclusions or similar imperfections or discontinuities in aninsulating system. It is possible that partial discharges willoriginate at locations such as on the leads or terminals withoutresulting in any hazard within the main part of the insulationsystem.6. Interference6.1 It is possible that radiated or conducted electricaldisturbances from sources ot