1、Designation:D363807 Designation: D3638 12An American National StandardStandard 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 adoptio
2、n 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.1. Scope*1.1 This test method evaluates in a short period of time the low-voltage (up t
3、o 600 V) track resistance or comparative trackingindex (CTI) of materials in the presence of aqueous contaminants.1.2 The values stated in metric (SI) units are to be regarded as standard. The inch-pound equivalents of the metric units areapproximate.1.3 This standard is technically equivalent to th
4、e version of IEC Publication 112 cited in 2.2. However, the 2007 version of IEC60112 Fourth Edition yields numerical CTI values that are very likely to differ significantly from this standard.1.4 This standard does not purport to address all of the safety problems, if any, associated with its use. I
5、t is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1711 Terminology Relating to Electrical InsulationD6054 Practice for Conditioning
6、 Electrical Insulating Materials for Testing2.2 IEC Publication:112 Recommended Method for Determining the Comparative Track Index of Solid Insulating Materials Under MoistConditions, 1971 Second Edition360112 Recommended Method for Determining the Comparative Track Index of Solid Insulating Materia
7、ls Under MoistConditions, 2007 Fourth Edition33. Terminology3.1 Definitions:3.1.1 tracka partially conducting path of localized deterioration on the surface of an insulating material.3.1.2 trackingthe process that produces tracks as a result of the action of electric discharges on or close to an ins
8、ulationsurface.3.1.3 tracking, contaminationtracking caused by scintillations that result from the increased surface conduction due tocontamination.3.1.4 tracking resistancethe quantitative expression of the voltage and the time required to develop a track under the specifiedconditions.3.1.5 For oth
9、er terminology, refer to Terminology D1711.3.2 Definitions of Terms Specific to This Standard:3.2.1 comparative tracking indexan index for electrical insulating materials which is arbitrarily defined as the numerical valueof that voltage which will cause failure by tracking when the number of drops
10、of contaminant required to cause failure is equalto 50.3.2.1.1 DiscussionThe voltage value is obtained from a plot of the number of drops required to cause failure by trackingversus the applied voltage.3.2.2 failure, nan attribute of an electrical circuit containing an electrical-current-sensing dev
11、ice that rapidly decreases the1This test method is under the jurisdiction of ASTM Committee D09 on Electrical and Electronic Insulating Materials and is the direct responsibility of SubcommitteeD09.12 on Electrical Tests.Current edition approved JuneJan. 1, 2007.2012. Published July 2007.February 20
12、12. Originally approved in 1977. Last previous edition approved in 19982007 asD363893(1998).D3638 07. DOI: 10.1520/D3638-07.10.1520/D3638-12.2For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume
13、 information, refer to the standards Document Summary page on the ASTM website.3Available from the International Electrotechnical Commission, Geneva, Switzerland.1This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have bee
14、n made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document
15、.*A Summary 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.applied voltage to zero if the current in the circuit exceeds a predetermined limit.4. Summary of Test Method4.1 The su
16、rface of a specimen of electrical insulating material is subjected to a low-voltage alternating stress combined witha low current which results from an aqueous contaminant (electrolyte) which is dropped between two opposing electrodes every30 s. The voltage applied across these electrodes is maintai
17、ned until the current between them exceeds a predetermined value. Thiscondition constitutes a failure.Additional specimens are tested at other voltages so that a relationship between applied voltage andnumber of drops to failure can be established through graphical means. The numerical value of the
18、voltage which causes failurewith the application of 50 drops of the electrolyte is arbitrarily called the comparative tracking index. This index provides anindication of the relative track resistance of the material.5. Significance and Use5.1 Electrical equipment can fail as a result of electrical t
19、racking of insulating material that is exposed to various contaminatingenvironments and surface conditions. There are a number of ASTM and other tests designed to quantify behavior of materials,especially at relatively high voltages. This method is an accelerated test which at relatively low test vo
20、ltages, provides acomparison of the performance of insulating materials under wet and contaminated conditions. The comparative tracking index isnot related directly to the suitable operating voltage in service.5.2 When organic electrical insulating materials are subjected to conduction currents betw
21、een electrodes on their surfaces, manyminute tree-like carbonaceous paths or tracks are developed near the electrodes. These tracks are oriented randomly, but generallypropagate between the electrodes under the influence of the applied potential difference. Eventually a series of tracks spans theele
22、ctrode gap, and failure occurs by shorting of the electrodes.5.3 The conditions specified herein are intended, as in other tracking test methods, to produce a condition conducive to theformation of surface discharges and possible subsequent tracking. Test conditions are chosen to reproducibly and co
23、nvenientlyaccelerate a process; for this reason, they rarely reproduce the varied conditions found in actual service. Therefore, while trackingtests serve to differentiate materials under given conditions, results of tracking tests cannot be used to infer either direct orcomparative service behavior
24、 of an application design. Rather, tracking test results provide a tool for judging the suitability ofmaterials for a given application. The suitability can only be verified through testing the design in actual end use or underconditions which simulate end use as closely as possible.6. Apparatus6.1
25、The simplified electrical circuitry used in this test is illustrated in Fig. 1. For necessary information on the cleanliness ofapparatus, see Annex A1. The essential components are as follows:6.1.1 Variable Power Source, consisting of a transformer type supply, such as the combination T1 and T2 in F
26、ig. 1, with avariable output of 0 to 1000 V, 60 Hz capable of maintaining a current of 1 A (1 kVA).6.1.2 Voltmeter (V1), capable of measuring the varying a-c output of the power source.A0 to 600-V voltmeter with an accuracyof at least 6 2.5 % of full scale.6.1.3 Ammeter (A1), with a range of 0 to 1
27、A a-c and an accuracy of at least 610 % of full scale.6.1.4 Current Limiting Resistor (R1), continuously variable, wire wound, rated at greater than 1 A.6.1.5 Shorting Switch (S1), single-pole single-throw rated at 1000 V and greater than 1 A. Note1The need for a shortingswitch can be considered opt
28、ional. It is possible to couple the variable resistor with the autotransformer which gives an automaticsetting of the current throughout the range of the instrument. Then whenever it is necessary to check the calibration of theinstrument, the shorting action can be accomplished by a jumper wire plac
29、ed across the electrodes. This coupling of theautotransformer with the variable resistor can be considered another option.6.1.66.1.5.1 A shorting switch is optional. See Annex A2.FIG. 1 Electrical Circuit ComponentsD3638 1226.1.6 Over-Current Relay (R0), which is inserted in the circuit shall not tr
30、ip at currents up to 0.1A. Use a relay having a trippingtime on short circuit of at least 0.5 s and a current limited on short circuit to 1 A with a tolerance of 610 % at a power factor of0.9 to 1.0. Note2Some instruments have used a Heinemann breaker, which is probably the closest standard commerci
31、al breakerto that described in the IEC Method. This breaker is Heinemann Model Series JA, Curve 2. The tripping action also can beaccomplished with suitable electronic circuitry.6.1.6.1 The tripping action can be accomplished with suitable electronic circuitry or with a commercial circuit breaker.46
32、.1.7 Testing Fixture, adjustable platform which supports the specimen and electrode setup.6.1.8 Platinum Electrodes, having a rectangular cross section measuring 5 by 2 mm (0.2 by 0.08 in.), extending 20 mm (0.8in) minimum from suitable mounting shanks (Fig. 2). Machine the end of each electrode to
33、form a 30 chisel-point edge, havinga radius from 0.05 to 0.10 mm, extending along the 5-mm (0.2-in) side of the electrode. This is the radius that generally resultsfrom polishing a “O mm” radius electrode. Since the direction of polish can influence the results, polish all electrodes in a directionp
34、erpendicular to the long dimension of the electrode face.6.1.9 Dropping Apparatus, capable of dropping the electrolyte precisely as specified in Section 9. Include in the droppingapparatus device for electrically starting and stopping the dropping of the electrolyte as well as a counting device for
35、monitoringthe number of drops. The orifice diameter of the drop mechanism is approximately 1.5 mm. If necessary, adjust this diameter soas to obtain the proper drop size in accordance with 9.2. The channel for electrolyte flow is called “the needle” in Annex A1.7. Reagents7.1 Electrolyte Solution of
36、 Ammonium Chloride in Water:7.1.1 Prepare a solution of ammonium chloride at an approximate concentration of 0.1 % by dissolving1gofreagent gradeammonium chloride in 1 L of water. Use water having a volume resistivity not less than 0.5 MV/cm at 23 C. Allow the solutionto stand overnight in a covered
37、, but not sealed, container.7.1.2 Calculate the resistivity of the solution using a conductivity cell and an a-c bridge, or meter, following the manufacturersinstructions. If the resistivity is 385 6 5 V/cm at 23 612 C, the solution is suitable for use in the test. If the resistivity is outsidethe a
38、bove limits, adjust the concentration until these limits are observed. Adjustment is accomplished by adding water or NH4Cl.7.1.3 Calibrate the conductivity cell with 0.01 N potassium chloride calibrating solution which is available from the cellmanufacturer.8. Test Specimens8.1 Typical test specimen
39、s can be 50-mm (2 in.) or 100-mm (4 in.) diameter disks or any other similar shape with a minimumthickness of 2.5 mm (0.100 in.). A similar shape is any shape that has essentially a flat (not curved) planar surface that has an areaof at least 2000 mm2and meets the requirements of 8.2 and 8.4. Test a
40、t least five specimens of each sample.8.2 In as much as variations in values can result from a lack of uniformity of dispersion of the material throughout any moldedspecimen or from surface imperfections on any specimen, care must be taken to prepare specimens that are as uniform as possible,both wi
41、thin the particular specimen and from one specimen to another.8.3 Condition specimens in accordance with Procedure A of Practice D6054.8.4 Specimens must be clean of dust, dirt, oil, or other contaminants with smooth surfaces and essentially free from scratches.8.5 Test thin materials by first clamp
42、ing them together tightly to form a specimen having a thickness as close as possible to therecommended thickness.9. Calibration and Standardization9.1 Partially support the electrodes by adjustable pivot arms so that the electrodes rest on the test specimen surface as shownin Fig. 2, exerting a forc
43、e of 100 g (3.5 oz).4The committee has been informed that the closest standard commercial breaker to that described in the IEC Method is Heinemann Model Series JA, Curve 2. Thecommittee has not independently verified this information nor does it endorse that particular breaker.FIG. 2 Electrodes (Rad
44、ius 0.05 to 0.1 mm)D3638 1239.2 The drop height for the electrolyte is to be not more than 40 mm (1.6 in.) above the electrode gap. The holding device isdesigned to store an aqueous solution and deliver periodically a measured drop to the specimen. The drop size is to be 20+50mm3(0.0015 in.3) and th
45、e drop rate is to be 1 drop/30 6 5 s. (The drop size can be measured by using a small calibrated graduateto accumulate a number of drops to obtain an accurate reading.)9.3 Allow approximately 15 drops of electrolyte to drop from the apparatus into a beaker or other container so as to removeany solut
46、ion with a high concentration of ammonium chloride.9.4 Reform the electrodes when the edges are rounded in excess of 0.1-mm diameter or when burrs or rough edges areobservable at 15 3 magnification. Replace electrodes when sharpening or machining fails to restore the specific dimensions of theelectr
47、odes and the quality of the chisel edge.9.5 Reproducibility of results is improved by abrasive cleaning of the electrodes after every two or three tests.9.6 The power source is set to the desired voltage with nothing but air between the electrodes (switch open). The shorting switchis closed and the
48、current limiting resistor adjusted to give a reading of 1 A.10. Procedure10.1 Conduct the test in a draft-free, clean environment at a temperature of 20 6 5 C.10.2 Fill the dropping assembly with solution and set the counter to 0.10.3 Set the power source to the desired voltage and adjust in accorda
49、nce with 9.6.10.4 Place the test specimen on the supporting platform so that the electrodes can be placed on the specimen.10.5 Position the electrodes as shown in Fig. 2 so that the chisel edges contact the specimen at a 60 angle between electrodesand so that the chisel faces are parallel in the vertical plane and are separated by 4 6 0.2 mm (0.16 in.).NOTE3It 1It is recommended that contact of the electrodes with the specimen 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 visibl
