1、Designation: D3638 12Standard Test Method forComparative Tracking Index of Electrical InsulatingMaterials1This standard is issued under the fixed designation D3638; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last r
2、evision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () 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 resistance or comparativetracking i
3、ndex (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 Publication 112 cited in 2.2. Howeve
4、r, 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 of the user of this standard to
5、establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1711 Terminology Relating to Electrical InsulationD6054 Practice for Conditioning Electrical Insulating Mate-rials for Testing (Withd
6、rawn 2012)32.2 IEC Publication:112 Recommended Method for Determining the Compara-tive Track Index of Solid Insulating Materials UnderMoist Conditions, 1971 Second Edition460112 Recommended Method for Determining the Com-parative Track Index of Solid Insulating Materials UnderMoist Conditions, 2007
7、Fourth Edition43. 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.3.1.3 tracking,
8、contaminationtracking caused by scintilla-tions 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, refer to Termin
9、ology D1711.3.2 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 required to caus
10、efailure 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 rapidly decreasesthe a
11、pplied 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 aqueouscontaminant (electrolyt
12、e) 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 relationship betwee
13、n applied voltage and number ofdrops to failure can be established through graphical means.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 app
14、roved Jan. 1, 2012. Published February 2012. Originallyapproved in 1977. Last previous edition approved in 2007 as D3638 07. DOI:10.1520/D3638-12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards
15、 volume information, refer to the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.4Available from the International Electrotechnical Commission, Geneva, Swit-zerland.*A Summary of Changes section appears at the en
16、d of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1The numerical value of the voltage which causes failure withthe application of 50 drops of the electrolyte is arbitrarilycalled the comparative tracking index. This ind
17、ex provides anindication of the relative track resistance of the material.5. Significance 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
18、 tests designed to quantifybehavior of materials, especially at relatively high voltages.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
19、not related directly to thesuitable operating voltage in service.5.2 When organic electrical 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 orientedr
20、andomly, but generally propagate between the electrodesunder the influence of the applied 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,
21、to produce a condition conducive to theformation of surface discharges and possible 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.Therefore, while tracking t
22、ests serve to differentiate materialsunder given conditions, results of tracking tests cannot be usedto infer 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 suitab
23、ility can only be verified through testing the designin actual end use or under conditions 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, see Annex
24、A1. The essential components areas follows:6.1.1 Variable Power Source, consisting 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 varyi
25、ng a-coutput of the power source. A0 to 600-V voltmeter with anaccuracy of at least 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 variable,wire wound, rated at greater than 1 A.
26、6.1.5 Shorting Switch (S1), single-pole single-throw rated at1000 V and greater than 1 A.6.1.5.1 A shorting switch is optional. See Annex A2.6.1.6 Over-Current Relay (R0), which is inserted in thecircuit shall not trip at currents up to 0.1 A. Use a relay havinga tripping time on short circuit of at
27、 least 0.5 s and a currentlimited on short circuit to 1 A with a tolerance of 610%atapower factor of 0.9 to 1.0.6.1.6.1 The tripping action can be accomplished with suit-able electronic circuitry or with a commercial circuit breaker.56.1.7 Testing Fixture, adjustable platform which supportsthe speci
28、men and electrode setup.6.1.8 Platinum Electrodes, having a rectangular cross sec-tion measuring 5 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,
29、extending alongthe 5-mm (0.2-in) side of the electrode. This is the radius thatgenerally results from 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 Droppi
30、ng Apparatus, capable of dropping the electro-lyte precisely as specified in Section 9. Include in 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 mechan
31、ism is approximately 1.5 mm. If necessary, adjust5The committee has been informed that the closest standard commercial breakerto that described in the IEC Method is Heinemann Model Series JA, Curve 2. Thecommittee has not independently verified this information nor does it endorse thatparticular bre
32、aker.FIG. 1 Electrical Circuit ComponentsD3638 122this 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 chlori
33、de at an ap-proximate concentration of 0.1 % by dissolving1gofreagentgrade ammonium chloride in 1 L of water. Use water having avolume resistivity not less than 0.5 M/cm at 23 C.Allow thesolution to stand overnight in a covered, but not sealed,container.7.1.2 Calculate the resistivity of the solutio
34、n using a con-ductivity cell and an a-c bridge, or meter, following themanufacturers instructions. If the resistivity is 385 6 5 /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. Adjus
35、tment is accomplished byadding water or NH4Cl.7.1.3 Calibrate 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 sh
36、ape with aminimum thickness of 2.5 mm (0.100 in.). A 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
37、 result from a lackof uniformity of dispersion of the material throughout anymolded specimen or from surface imperfections on anyspecimen, 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 specime
38、ns in accordance with ProcedureAofPractice D6054.8.4 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 th
39、e recommended thickness.9. Calibration and Standardization9.1 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
40、.6 in.) above the electrode gap. The holding device 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 gradu
41、ate to accumulate a number of drops to obtainan accurate 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
42、inexcess of 0.1-mm diameter or when burrs or rough edges areobservable at 15 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
43、the electrodes after every two or three tests.9.6 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-fre
44、e, clean environment at atemperature of 20 6 5 C.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.FIG. 2 Electrodes (Radius 0.05 to 0.1 mm)D3638 12310.4 Place the test specimen on the supporting pl
45、atform sothat the electrodes can be placed on the specimen.10.5 Position the electrodes as shown in 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 1It i
46、s recommended that contact of the electrodes with thespecimen shall be such that when a light source is so placed that the lightreaches the eye along the surface of the specimen, no light is visiblebetween the specimen and the electrodes. If light is visible due to theelectrode edges having become r
47、ounded, the edges must be reground.10.6 Open the 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
48、 A) accompanied by a corre-sponding drop in voltage.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-spl
49、ashed 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 Limit any test voltage to 600 V or less. Testing athigher voltages will generate electric discharges above thesurface of the specimen, which will produce erroneous results.10.11 When testing at voltages below 150 V, and there is notsufficient energ
