Designation:D 2303–97
An American National Standard
Standard Test Methods for
Liquid-Contaminant,Inclined-Plane Tracking and Erosion of Insulating Materials 1
This standard is issued under the fixed designation D 2303;the number immediately following the designation indicates the year of original adoption or,in the case of revision,the year of last revision.A number 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
1.1These test methods cover the evaluation of the relative tracking and erosion resistance of insulating solids using the liquid-contaminant,inclined-plane test.2The following test methods also can be used to evaluate the tracking resistance of materials:D 2132(contaminants:dust and fog)and D 3638(contaminant:conductive liquid drops).
1.2Two tracking and one erosion test procedure are de-scribed:
1.2.1A “variable voltage method”to evaluate resistance to tracking.
1.2.2A “time-to-track method”to evaluate resistance to tracking.
1.2.3A method for quantitative determination of erosion (Annex A1).
1.3While a particular contaminant solution is specified,other concentrations of the same contaminant,or different contaminants may be used to simulate different environmental or service conditions.
1.4The values stated in inch-pound units are to be regarded as the standard.
1.5This standard does not purport to address all of the safety concerns,if any,associated with its use.It is the responsibility 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 precau-tionary statements are given in Section 8.
2.Referenced Documents 2.1ASTM Standards:
D 374Test Methods for Thickness of Solid Electrical Insu-lation 3
D 1711Terminology Relating to Electrical Insulation 3
D 2132Test Method for Dust-and Fog-Tracking and Ero-sion Resistance of Electrical Insulating Materials 3
D 3638Test Method for Comparative Tracking Index of Electrical Insulating Materials 43.Terminology 3.1Definitions:
3.1.1erosion,electrical ,n —the progressive wearing away of electrical insulation by the action of electrical discharges.3.1.2erosion resistance,electrical ,n —the quantitative expression of the amount of electrical erosion under specific conditions.
3.1.3track ,n —a partially conducting path of localized deterioration on the surface of an insulating material.
3.1.4tracking ,n —the process that produces tracks as a result of the action of electric discharges on or close to the insulation surface.
3.1.5tracking,contamination,n —tracking caused by scin-tillations that result from the increased surface conduction due to contamination.
3.1.6tracking resistance ,n —the quantitative expression of the voltage and the time required to develop a track under specified conditions.
3.2Definitions of Terms Specific to This Standard:
3.2.1initial tracking voltage ,n —the applied voltage at which continuous tracking can be initiated in a specified time.3.2.2time-to-track ,n —the time in which tracking proceeds a specified distance between the test electrodes at a specified voltage.
3.3Other definitions pertinent to these test methods are given in Terminology D 1711.
4.Significance and Use
4.1These test methods differentiate among solid electrical insulating materials on the basis of their resistance to the action of voltage stresses along the surface of the solid when wet with an ionizable,electrically conductive,liquid contaminant.
4.2These test methods quantitatively evaluate,in a relative manner,the effects upon an insulating material resulting from
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These test methods are under the jurisdiction of ASTM Committee D-9on Electrical and Electronic Insulating Materials and are the direct responsibility of Subcommittee D09.12on Electrical and Electronic Tests.
Current edition approved Sept.10,1997.Published November 1997.Originally issued as D 2303–64T.Last previous edition D 2303–96.2
K.N.Mathes,Chapter 4,“Surface Failure Measurements,”Engineering Dielectrics,Vol IIB,Electrical Properties of Solid Insulating Materials,Measure-ment Techniques ,R.Bartnikas,Editor,ASTM STP 926,ASTM,Philadelphia,1987.3
Annual Book of ASTM Standards ,V ol 10.01.
4
Annual Book of ASTM Standards ,V ol 10.02.
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Copyright ©ASTM International,100Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.
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the action of electrical discharges upon a material surface.The effects are similar to those that may occur in service under the influence of dirt combined with moisture condensed from the atmosphere.
4.2.1In the field,the conditions resulting in electrical discharges occur sporadically.Degradation,often in the form of a conducting “track”,develops very slowly until it ulti-mately bridges the space between conductors thus causing complete electrical breakdown.
4.2.2In these test methods,the conducting liquid contami-nant is continuously supplied at an optimum rate to the surface of a test specimen in such a fashion that essentially continuous electrical discharge can be maintained.
4.2.3By producing continuous surface discharge with con-trolled energy it is possible,within a few hours,to cause specimen failure which is similar to failure occurring under long-time exposure to the erratic conditions of service in the field.
4.2.4The test conditions,which are standardized and accel-erated,do not reproduce all of the conditions encountered in service.Use caution when making either direct or comparative service behavior inferences derived from the results of tracking tests.
4.3The time-to-track a 1-in.(25-mm)distance at a specified voltage between electrodes separated 2in.(50mm)has also been found useful in categorizing insulating materials for indoor and protected outdoor applications,such as metal-clad switchgear.
4.4The initial tracking voltage has been found useful for evaluating insulating materials to be used at high voltages or outdoors and unprotected,as well as for establishing (see 10.1)the test voltage for the time-to-track test.
4.5In service many types of contamination may cause tracking and erosion of different materials to different degrees.This method recognizes the importance of such variability and suggests the use of special test solutions to meet specific service needs.For example,an ionic contaminant containing,in addition,a carbonaceous component such as sugar may be used to cause tracking on very resistant materials like polym-ethylmethacrylate.Such contamination may be representative of some severe industrial environments.In this case,the time-to-track technique is used,since time is required to decompose the contaminant solution and build up conducting residues on the sample surface.
4.6Very track-resistant materials,such as polymethyl-methacrylate,may erode rather than track under more usual contaminant conditions in service.The use of this method for measuring erosion is consequently important.For erosion studies,only tests as a function of time at constant voltage are useful.
5.Apparatus
5.1A simple schematic diagram of the apparatus is given in Fig.1and consists of the following.Details are given in Annex
A2.
FIG.1Schematic Diagram of
Apparatus
5.1.1A 60-Hz power supply with an output voltage stabi-lized to 61%which can be varied from 1to at least 7.5kV with a rated current of no less than 0.1A for every test station to be used (that is,0.5A for five stations).
5.1.2A means for applying a specified contaminant solution at a controlled rate to the specimen surface.A pneumatically actuated repeating pipet has been found useful for this purpose and is described in Annex A2.Peristaltic pumps have also been used (A2).
5.1.3Stainless steel top and bottom electrodes as shown in Fig.2.
N OTE 1—Stainless-steel type 302is recommended.
5.1.4A pad of filter paper cut as shown in Fig.3to fit under the top electrode and used to smooth out the flow of the contaminant solution.
5.1.5A set of ballast resistors (50,10,and 1-k V rated at 200W each)to be connected as specified in series with each test specimen on the high-voltage side of the power supply.Somewhat lower resistances are being considered by the International Electrotechnical Commission (IEC/TC15).
5.1.6A 330-V ,1⁄2-W,carbon resistor 5mounted with a simple tension spring and connected in series with the speci-men and ground to act as an overload,high-voltage fuse.5.1.7Structural parts and a grounded safety enclosure.
6.Sampling
6.1Refer to applicable materials specifications for sampling instructions.
7.Test Specimens
7.1Make insulation specimens with a flat surface approxi-
mately 2by 5in.(50by 130mm)as shown in Fig.4.Measure the thickness in accordance with Test Methods D 374if there is no standard for a particular material.Specimens must be thick enough that tracking does not penetrate completely through the specimen during the test.Secure thin specimens to prevent sagging.Specimens thicker than 3⁄4in.(2cm)are difficult to clamp in the apparatus.
7.2Prepare separate specimens exposing each surface of sheet or other materials with two or more surfaces which may have different characteristics.Carefully identify the surface so
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International Resistance Co.RC 20-mil type carbon-composition resistors,available from the TRW Electronics Corp.,Commerce Terminal Bldg.,Philadelphia,PA,have been found
satisfactory.
FIG.2Top and Bottom
Electrodes
far as possible,that is,mold face,press face,etc.Prepare two sets of specimens of materials with notice
able directional characteristics,with the predominant directional characteristic in line with the electrodes for one set and at right angles to the other set.Identify the specimen direction as far as possible;that is,machine direction,cross-machine direction,warp or fill direction (for woven textile reinforced products).Fig.5
7.3Preparation of Specimens —Clean the specimen face with a suitable solvent 6and rinse with distilled water.For specimens to be used in the time-to-track method,do not mechanically destroy,that is,sand,abrade,etc.the natural surface finish of the specimen unless otherwise specified.However,with the variable-voltage method,the surface of the test specimens should be lightly but completely sanded under flowing tap water with 400A-grit wet silicon carbide paper and rinsed with distilled water.Such sanding removes gloss and contaminants to provide a surface that is wet more easily and rapidly by the contaminant.Loss of gloss and slight erosion of the surface usually occurs in service,particularly outdoors.Generously cover the specimen area under the bottom elec-trode with conductive silver paint 7and add the 1-in.(25-mm)tracking reference marks as shown in Fig.5.For all tests,other than the time-to-track test,soak the test specimens prepared as above for 24to 48h in the specified contaminant solution before test.
7.4Prepare five specimens for each determination.8.Procedure
8.1Lethal voltages are a potential hazard during the performance of this test.It is essential that the test apparatus,and all associated equipment electrically connected to it,be properly designed and installed for safe operation.Solidly ground all electrically conductive parts which it is possible for a person to contact during the test.Provide means for use at the completion of any test to ground any parts which were at high voltage during the test or have the potential for acquiring an induced charge during the test or retaining a charge even after disconnection of the voltage source.Thoroughly instruct
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The solvent should not soften or otherwise damage the test specimen.Isopropyl alcohol has been found suitable for many materials.7
DuPont silver paint No.4817has been found suitable for this
purpose.
FIG.3Filter Paper,Showing Clip and Method of
Fastening
FIG.4Test
Specimen
FIG.5Test Specimen Showing Location of Conducting Silver
Paint and Tracking Reference
Marks
all operators as to the correct procedures for performing tests safely.When making high voltage tests,particularly in com-pressed gas or in oil,it is possible for the energy released at breakdown to be suffıcient to result in fire,explosion,or rupture of the test chamber.Design test equipment,test chambers,and test specimens so as to minimize the possibility of such occurrences and to eliminate the possibility of personal injury.If the potential for fire exists,have fire suppression equipment available .
8.1.1Also see Fig.1.
8.2Mount and fuse the specimen with the flat test surface on the underside at an angle of 45°from the horizontal as shown in Fig.1.Insert the contaminant delivery hose midway between eight thicknesses of the filter paper as shown in Fig.3(c )and fold back the filter paper “ear”to prevent contaminant from squirting out the sides.
8.3At the start of each test date,replace all residual liquid in the contaminant supply beaker with fresh contaminant.Cover all beakers to minimize dust and dirt as well as evaporation.Unless otherwise specified,use 0.1%(by weight)ammonium chloride (reagent grade)and 0.02%nonionic wetting agent 8in distilled water.This contaminant solution
must have a resistivity between 370and 400V -cm when measured at 2361°C.
8.4Adjust the contaminant flow and calibrate as described in Annex A1to give the flow rate for the voltage to be specified in Table 1.
8.5After calibration,the start-up procedure differs,depend-ing on whether the test specimen is a carry-over from a previous test,or an entirely new specimen.
8.5.1For a specimen that has never been subjected to voltages and contaminant (that is,new specime
n),start the contaminant injection into the filter paper,allowing the fresh contaminant to wet the filter paper thoroughly and replace the old liquid in the tubes and syringes and to flow as a steady stream (Note 2)(not intermittent bursts)across the test specimen face between electrodes.The contaminant must flow from the quill hole in the bottom of the top electrode and should not squirt out of the sides or top of the filter paper during the pressure stroke of the pipet.Adjust the specimens so that the contaminant runs down as nearly as possible the center line of the specimen.Avoid drafts on equipment that might cause undue cooling of the specimens or of the water vapor from evaporation of the contaminant.Close the safety gate and apply the appropriate test voltage tabulated in Table 1.
N OTE 2—This steady flow condition should be observed for 5min at the normal test contaminant feed rate and not at a manually operated accelerated calibration rate.
8.5.2For a specimen that is a continuation from a previous test (that is,off test overnight),wash down the test specimen face and filter paper with distilled water in order to remove any contaminant residue from the previous test.Do not change the filter paper.Start the contaminant flow,allowing the fresh contaminant to wet the filter paper thoroughly,and replace the old liquid in the tubes and syringes until a steady contaminant flow (Note 2)is established across the specimen face.Momen-tarily arrest the contaminant injection into the filter paper,and inject 2mL of distilled water into the filter paper with a ma
nual syringe.Quickly rewash the specimen face only with distilled water,close the safety gate,start up the contaminant flow,and apply the required voltage.Time is of the essence here,for any prolonged delay will result in a too vigorous and faulty start-up.
8.6Effective scintillation,small yellow to white (perhaps with some parts blue)arcs,should appear predominantly just above the teeth of the lower electrode within at most a very few minutes after application of the voltage.These discharges should occur in essentially continuous fashion,although they may “dance”from one tooth to another before finally settling down to cause a small,bright “hot spot”which will start“chewing”on the specimen surface and which will ultimately lead to tracking failure.The condition of effective scintillation can also be observed with a cathode-ray oscilloscope.The signal may be picked off the ungrounded side of the fuse resistor.Proper scintillation is observed as a continual but nonuniform break-up of the 60-Hz current wave over the whole duration of each half cycle.Effective scintillation is critical and if not obtained,then the electrical circuit,the contaminant flow characteristics,and the contaminant conductivity must be carefully checked and adjusted if necessary.
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Triton X-100made by Rohm and Haas Co.,Philadelphia,PA,has been found satisfactory.It should be added to a small portion of the water and thoroughly mixed before being added to the larger bulk.
TABLE 1Rates of Contaminant Application
N OTE 1—The rates of contaminant application shown are suitable only for contaminants with a resistivity of approximately 370to 400V ·cm at 23°C on nonporous samples.With porous samples it may be nesessary to increase the contaminant flow somewhat to maintain effective,continual scintillation.Lower contaminant resistivities also will require a higher rate and higher resistivities,a lower rate of contaminant application;this must be determined experimentally.At too high a contaminant rate scintillation will be greatly reduced because the current will flow in the contaminant film without disrupting it.At too low a rate the solution boils away or at the higher voltages is electrostatically removed so that scintillation occurs only at intervals in scattered bursts.A The tendency for tracking and erosion is increased with a decrease in contaminant resistivity or with the incorporation of a carbonaceous material such as sugar,even though in the latter case the resistivity is not decreased.The chemical nature of the ionizable contaminant is usually of minor importance in respect to tracking but may be of major importance in respect to erosion.
Rate of Application of 0.1%NH 4Cl-0.02%Wetting Agent,
mL/min
Voltage Range,kV Series Resistor,
editor evaluating revisionV 0.075  1.0B to 1.7510000.15  2.0to 2.75100000.30  3.0to 3.75500000.60  4.0to 4.75500000.90
5.0to
6.0
50
000
A
Mathes,K.N.,and McGowan,E.J.,“Surface Electrical Failure in the Presence of Contaminants.The Inclined-Plane,Liquid-Contaminant Test,”Transactions ,Part I ,Communications and Electronics ,Am.Inst.Electrical Engrs.,TEECA,July,1961(AIEE Preprint 61-21).B
Scintillation at 1kV is very critical,and it may be desirable to remove the series resistor and to decrease further the contaminant rate,that is,so that 0.075mL is applied only once every 2min.With such slow rat
es,it is possible also to obtain scintillation at voltages even lower than 1kV to permit test of relatively poor
materials.

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