ASTM D3638-07
(Test Method)Standard Test Method for Comparative Tracking Index of Electrical Insulating Materials
Standard Test Method for Comparative Tracking Index of Electrical Insulating Materials
SIGNIFICANCE AND USE
Electrical equipment can fail as a result of electrical tracking of insulating material that is exposed to various contaminating environments 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 voltages, provides a comparison of the performance of insulating materials under wet and contaminated conditions. The comparative tracking index is not related directly to the suitable operating voltage in service.
When organic electrical insulating materials are subjected to conduction currents between electrodes on their surfaces, many minute tree-like carbonaceous paths or tracks are developed near the electrodes. These tracks are oriented randomly, but generally propagate between the electrodes under the influence of the applied potential difference. Eventually a series of tracks spans the electrode gap, and failure occurs by shorting of the electrodes.
The conditions specified herein are intended, as in other tracking test methods, to produce a condition conducive to the formation of surface discharges and possible subsequent tracking. Test conditions are chosen to reproducibly and conveniently accelerate a process; for this reason, they rarely reproduce the varied conditions found in actual service. Therefore, while tracking tests serve to differentiate materials under given conditions, results of tracking tests cannot be used to infer either direct or comparative service behavior of an application design. Rather, tracking test results provide a tool for judging the suitability of materials for a given application. The suitability can only be verified through testing the design in actual end use or under conditions which simulate end use as closely as possible.
SCOPE
1.1 This test method evaluates in a short period of time the low-voltage (up to 600 V) track resistance or comparative tracking index (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 are approximate.
1.3 This standard is technically equivalent to the version of IEC Publication 112 cited in . However, the 2007 version of IEC 60112 Fourth Edition yields numerical CTI values that are very likely to differ significantly from this standard.
This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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An American National Standard
Designation:D3638–07
Standard Test Method for
Comparative Tracking Index of Electrical Insulating
1
Materials
This standard is issued under the fixed designation D3638; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* parative Track Index of Solid Insulating Materials Under
3
Moist Conditions, 2007 Fourth Edition
1.1 This test method evaluates in a short period of time the
low-voltage (up to 600 V) track resistance or comparative
3. Terminology
tracking index (CTI) of materials in the presence of aqueous
3.1 Definitions:
contaminants.
3.1.1 track—a partially conducting path of localized dete-
1.2 The values stated in metric (SI) units are to be regarded
rioration on the surface of an insulating material.
as standard.The inch-pound equivalents of the metric units are
3.1.2 tracking—the process that produces tracks as a result
approximate.
of the action of electric discharges on or close to an insulation
1.3 This standard is technically equivalent to the version of
surface.
IECPublication 112citedin2.2.However,the2007versionof
3.1.3 tracking, contamination—tracking caused by scintil-
IEC60112FourthEditionyieldsnumericalCTIvaluesthatare
lations that result from the increased surface conduction due to
very likely to differ significantly from this standard.
contamination.
1.4 This standard does not purport to address all of the
3.1.4 tracking resistance—thequantitativeexpressionofthe
safety problems, if any, associated with its use. It is the
voltage and the time required to develop a track under the
responsibility of the user of this standard to establish appro-
specified conditions.
priate safety and health practices and determine the applica-
3.1.5 For other terminology, refer to Terminology D1711.
bility of regulatory limitations prior to use.
3.2 Definitions of Terms Specific to This Standard:
2. Referenced Documents 3.2.1 comparative tracking index—an index for electrical
2
insulating materials which is arbitrarily defined as the numeri-
2.1 ASTM Standards:
cal value of that voltage which will cause failure by tracking
D1711 Terminology Relating to Electrical Insulation
when the number of drops of contaminant required to cause
D6054 Practice for Conditioning Electrical Insulating Ma-
failure is equal to 50.
terials for Testing
3.2.1.1 Discussion—The voltage value is obtained from a
2.2 IEC Publication:
plot of the number of drops required to cause failure by
112 Recommended Method for Determining the Compara-
tracking versus the applied voltage.
tive Track Index of Solid Insulating Materials Under
3
3.2.2 failure, n—an attribute of an electrical circuit contain-
Moist Conditions, 1971 Second Edition
ing an electrical-current-sensing device that rapidly decreases
60112 Recommended Method for Determining the Com-
the applied voltage to zero if the current in the circuit exceeds
a predetermined limit.
1
This test method is under the jurisdiction of ASTM Committee D09 on
4. Summary of Test Method
Electrical and Electronic Insulating Materials and is the direct responsibility of
Subcommittee D09.12 on Electrical Tests. 4.1 The surface of a specimen of electrical insulating
CurrenteditionapprovedJune1,2007.PublishedJuly2007.Originallyapproved
material is subjected to a low-voltage alternating stress com-
in 1977. Last previous edition approved in 1998 as D3638–93(1998). DOI:
bined with a low current which results from an aqueous
10.1520/D3638-07.
2
contaminant (electrolyte) which is dropped between two op-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
posing electrodes every 30 s. The voltage applied across these
Standards volume information, refer to the standard’s Document Summary page on
electrodes is maintained until the current between them ex-
the ASTM website.
3 ceeds a predetermined value. This condition constitutes a
Available from the International Electrotechnical Commission, Geneva, Swit-
zerland.
failure. Additional specimens are tested at other voltages so
*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.
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D3638–07
that a relationship between applied voltage and number of 6.1.1 Variable Power Source, consisting of a transformer
drops to failure can be established through graphical means. type supply, such as the combinationT1 andT2 in Fig. 1, with
The numerical value of t
...
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