1、Designation: D 3638 07An American National StandardStandard Test Method forComparative Tracking Index of Electrical InsulatingMaterials1This standard is issued under the fixed designation D 3638; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method evaluates in a short period of time thelow-voltage (up to 600 V) track res
3、istance or comparativetracking index (CTI) of materials in the presence of aqueouscontaminants.1.2 The values stated in metric (SI) units are to be regardedas standard. The inch-pound equivalents of the metric units areapproximate.1.3 This standard is technically equivalent to the version ofIEC Publ
4、ication 112 cited in 2.2. However, the 2007 version ofIEC 60112 Fourth Edition yields numerical CTI values that arevery likely to differ significantly from this standard.1.4 This standard does not purport to address all of thesafety problems, if any, associated with its use. It is theresponsibility
5、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.2. Referenced Documents2.1 ASTM Standards:2D 1711 Terminology Relating to Electrical InsulationD 6054 Practice for Conditioning Electrical Insula
6、ting Ma-terials for Testing2.2 IEC Publication:112 Recommended Method for Determining the Compara-tive Track Index of Solid Insulating Materials UnderMoist Conditions, 1971 Second Edition360112 Recommended Method for Determining the Com-parative Track Index of Solid Insulating Materials UnderMoist C
7、onditions, 2007 Fourth Edition33. Terminology3.1 Definitions:3.1.1 tracka partially conducting path of localized dete-rioration on the surface of an insulating material.3.1.2 trackingthe process that produces tracks as a resultof the action of electric discharges on or close to an insulationsurface.
8、3.1.3 tracking, contaminationtracking caused by scintil-lations that result from the increased surface conduction due tocontamination.3.1.4 tracking resistancethe quantitative expression of thevoltage and the time required to develop a track under thespecified conditions.3.1.5 For other terminology,
9、 refer to Terminology D 1711.3.2 Definitions of Terms Specific to This Standard:3.2.1 comparative tracking indexan index for electricalinsulating materials which is arbitrarily defined as the numeri-cal value of that voltage which will cause failure by trackingwhen the number of drops of contaminant
10、 required to causefailure is equal to 50.3.2.1.1 DiscussionThe voltage value is obtained from aplot of the number of drops required to cause failure bytracking versus the applied voltage.3.2.2 failure, nan attribute of an electrical circuit contain-ing an electrical-current-sensing device that rapid
11、ly decreasesthe applied voltage to zero if the current in the circuit exceedsa predetermined limit.4. Summary of Test Method4.1 The surface of a specimen of electrical insulatingmaterial is subjected to a low-voltage alternating stress com-bined with a low current which results from an aqueouscontam
12、inant (electrolyte) which is dropped between two op-posing electrodes every 30 s. The voltage applied across theseelectrodes is maintained until the current between them ex-ceeds a predetermined value. This condition constitutes afailure. Additional specimens are tested at other voltages sothat a re
13、lationship between applied voltage and number ofdrops to failure can be established through graphical means.The numerical value of the voltage which causes failure withthe application of 50 drops of the electrolyte is arbitrarily1This test method is under the jurisdiction of ASTM Committee D09 onEle
14、ctrical and Electronic Insulating Materials and is the direct responsibility ofSubcommittee D09.12 on Electrical Tests.Current edition approved June 1, 2007. Published July 2007. Originally approvedin 1977. Last previous edition approved in 1998 as D 3638 93 (1998).2For referenced ASTM standards, vi
15、sit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from the International Electrotechnical Commission, Geneva, Swit-zerland.1*A Summary
16、 of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.called the comparative tracking index. This index provides anindication of the relative track resistance of the material.5. Signif
17、icance and Use5.1 Electrical equipment can fail as a result of electricaltracking of insulating material that is exposed to variouscontaminating environments and surface conditions. There area number of ASTM and other tests designed to quantifybehavior of materials, especially at relatively high vol
18、tages.This method is an accelerated test which at relatively low testvoltages, provides a comparison of the performance of insu-lating materials under wet and contaminated conditions. Thecomparative tracking index is not related directly to thesuitable operating voltage in service.5.2 When organic e
19、lectrical insulating materials are sub-jected to conduction currents between electrodes on theirsurfaces, many minute tree-like carbonaceous paths or tracksare developed near the electrodes. These tracks are orientedrandomly, but generally propagate between the electrodesunder the influence of the a
20、pplied potential difference. Even-tually a series of tracks spans the electrode gap, and failureoccurs by shorting of the electrodes.5.3 The conditions specified herein are intended, as in othertracking test methods, to produce a condition conducive to theformation of surface discharges and possible
21、 subsequent track-ing. Test conditions are chosen to reproducibly and conve-niently accelerate a process; for this reason, they rarelyreproduce the varied conditions found in actual service. There-fore, while tracking tests serve to differentiate materials undergiven conditions, results of tracking
22、tests cannot be used toinfer either direct or comparative service behavior of anapplication design. Rather, tracking test results provide a toolfor judging the suitability of materials for a given application.The suitability can only be verified through testing the designin actual end use or under c
23、onditions which simulate end use asclosely as possible.6. Apparatus6.1 The simplified electrical circuitry used in this test isillustrated in Fig. 1. For necessary information on the cleanli-ness of apparatus, seeAnnexA1. The essential components areas follows:6.1.1 Variable Power Source, consisting
24、 of a transformertype supply, such as the combination T1 and T2 in Fig. 1, witha variable output of 0 to 1000 V, 60 Hz capable of maintaininga current of 1 A (1 kVA).6.1.2 Voltmeter (V1), capable of measuring the varying a-coutput of the power source. A 0 to 600-V voltmeter with anaccuracy of at lea
25、st 6 2.5 % of full scale.6.1.3 Ammeter (A1), with a range of 0 to 1 A a-c and anaccuracy of at least 610 % of full scale.6.1.4 Current Limiting Resistor (R1), continuously vari-able, wire wound, rated at greater than 1 A.6.1.5 Shorting Switch (S1), single-pole single-throw ratedat 1000 V and greater
26、 than 1 A.NOTE 1The need for a shorting switch can be considered optional. Itis possible to couple the variable resistor with the autotransformer whichgives an automatic setting of the current throughout the range of theinstrument. Then whenever it is necessary to check the calibration of theinstrum
27、ent, the shorting action can be accomplished by a jumper wireplaced across the electrodes. This coupling of the autotransformer with thevariable resistor can be considered another option.6.1.6 Over-Current Relay (R0), which is inserted in thecircuit shall not trip at currents up to 0.1 A. Use a rela
28、y havinga tripping time on short circuit of at least 0.5 s and a currentlimited on short circuit to 1 A with a tolerance of 610%atapower factor of 0.9 to 1.0.NOTE 2Some instruments have used a Heinemann breaker, which isprobably the closest standard commercial breaker to that described in theIEC Met
29、hod. This breaker is Heinemann Model Series JA, Curve 2. Thetripping action also can be accomplished with suitable electronic circuitry.6.1.7 Testing Fixture, adjustable platform which supportsthe specimen and electrode setup.6.1.8 Platinum Electrodes, having a rectangular cross sec-tion measuring 5
30、 by 2 mm (0.2 by 0.08 in.), extending 20 mm(0.8 in) minimum from suitable mounting shanks (Fig. 2).Machine the end of each electrode to form a 30 chisel-pointedge, having a radius from 0.05 to 0.10 mm, extending alongthe 5-mm (0.2-in) side of the electrode. This is the radius thatgenerally results f
31、rom polishing a “O mm” radius electrode.Since the direction of polish can influence the results, polish allelectrodes in a direction perpendicular to the long dimension ofthe electrode face.6.1.9 Dropping Apparatus, capable of dropping the electro-lyte precisely as specified in Section 9. Include in
32、 the droppingapparatus device for electrically starting and stopping thedropping of the electrolyte as well as a counting device formonitoring the number of drops. The orifice diameter of thedrop mechanism is approximately 1.5 mm. If necessary, adjustFIG. 1 Electrical Circuit ComponentsD3638072this
33、diameter so as to obtain the proper drop size in accordancewith 9.2. The channel for electrolyte flow is called “the needle”in Annex A1.7. Reagents7.1 Electrolyte Solution of Ammonium Chloride in Water:7.1.1 Prepare a solution of ammonium chloride at an ap-proximate concentration of 0.1 % by dissolv
34、ing1gofreagentgrade ammonium chloride in 1 L of water. Use water having avolume resistivity not less than 0.5 MV/cm at 23 C.Allow thesolution to stand overnight in a covered, but not sealed,container.7.1.2 Calculate the resistivity of the solution using a con-ductivity cell and an a-c bridge, or met
35、er, following themanufacturers instructions. If the resistivity is 385 6 5 V/cmat 23 612 C, the solution is suitable for use in the test. If theresistivity is outside the above limits, adjust the concentrationuntil these limits are observed. Adjustment is accomplished byadding water or NH4Cl.7.1.3 C
36、alibrate the conductivity cell with 0.01 N potassiumchloride calibrating solution which is available from the cellmanufacturer.8. Test Specimens8.1 Typical test specimens can be 50-mm (2 in.) or 100-mm(4 in.) diameter disks or any other similar shape with aminimum thickness of 2.5 mm (0.100 in.). A
37、similar shape isany shape that has essentially a flat (not curved) planar surfacethat has an area of at least 2000 mm2and meets the require-ments of 8.2 and 8.4. Test at least five specimens of eachsample.8.2 In as much as variations in values can result from a lackof uniformity of dispersion of the
38、 material throughout anymolded specimen or from surface imperfections on any speci-men, care must be taken to prepare specimens that are asuniform as possible, both within the particular specimen andfrom one specimen to another.8.3 Condition specimens in accordance with ProcedureAofPractice D 6054.8
39、.4 Specimens must be clean of dust, dirt, oil, or othercontaminants with smooth surfaces and essentially free fromscratches.8.5 Test thin materials by first clamping them togethertightly to form a specimen having a thickness as close aspossible to the recommended thickness.9. Calibration and Standar
40、dization9.1 Partially support the electrodes by adjustable pivot armsso that the electrodes rest on the test specimen surface asshown in Fig. 2, exerting a force of 100 g (3.5 oz).9.2 The drop height for the electrolyte is to be not more than40 mm (1.6 in.) above the electrode gap. The holding devic
41、e isdesigned to store an aqueous solution and deliver periodicallya measured drop to the specimen. The drop size is to be20+50 mm3(0.0015 in.3) and the drop rate is to be 1drop/30 6 5 s. (The drop size can be measured by using a smallcalibrated graduate to accumulate a number of drops to obtainan ac
42、curate reading.)9.3 Allow approximately 15 drops of electrolyte to dropfrom the apparatus into a beaker or other container so as toremove any solution with a high concentration of ammoniumchloride.9.4 Reform the electrodes when the edges are rounded inexcess of 0.1-mm diameter or when burrs or rough
43、 edges areobservable at 15 3 magnification. Replace electrodes whensharpening or machining fails to restore the specific dimen-sions of the electrodes and the quality of the chisel edge.9.5 Reproducibility of results is improved by abrasivecleaning of the electrodes after every two or three tests.9.
44、6 The power source is set to the desired voltage withnothing but air between the electrodes (switch open). Theshorting switch is closed and the current limiting resistoradjusted to give a reading of 1 A.10. Procedure10.1 Conduct the test in a draft-free, clean environment at atemperature of 20 6 5 C
45、.10.2 Fill the dropping assembly with solution and set thecounter to 0.10.3 Set the power source to the desired voltage and adjustin accordance with 9.6.10.4 Place the test specimen on the supporting platform sothat the electrodes can be placed on the specimen.10.5 Position the electrodes as shown i
46、n Fig. 2 so that thechisel edges contact the specimen at a 60 angle betweenelectrodes and so that the chisel faces are parallel in the verticalplane and are separated by 4 6 0.2 mm (0.16 in.).NOTE 3It is recommended that contact of the electrodes with thespecimen shall be such that when a light sour
47、ce is so placed that the lightreaches the eye along the surface of the specimen, no light is visibleFIG. 2 Electrodes (Radius 0.05 to 0.1 mm)D3638073between the specimen and the electrodes. If light is visible due to theelectrode edges having become rounded, the edges must be reground.10.6 Open the
48、shorting switch and begin the sequence ofdrops with the time interval between drops set at 30 6 5s.10.7 Continue until tracking occurs. This condition is usu-ally well defined with a sudden surge occurring in the current(from essentially 0 to almost 1 A) accompanied by a corre-sponding drop in volta
49、ge.10.8 A test is permitted to be repeated on a given specimenprovided the electrode gap is positioned a minimum of 25 mm(1.0 in.) from any specimen area affected by a previous test orfrom any edge. The position of the new test must be clean andun-splashed with electrolyte from a prior test.10.9 Obtain one reading on each of five specimens of asample to be tested at any given voltage. Repeat this process inaccordance with 10.8, at different voltage levels such that atleast two levels produce failures in less than 50 drops and twolevels greater than 50 drops.10.10 Li
