ASTM D1932 - 19

    Standard Test Method for Thermal Endurance of Flexible Electrical Insulating Varnishes

    Active Standard ASTM D1932 | Developed by Subcommittee: D09.01

    Book of Standards Volume: 10.01


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    Significance and Use

    5.1 A major factor affecting the long term performance of insulating materials is thermal degradation. It is possible that factors, such as moisture and vibration, will cause failures after the material has been weakened by thermal degradation.

    5.2 An electrical insulating varnish is effective in protecting electrical equipment only as long as it retains its physical and electrical integrity.

    5.3 The thermal degradation of the varnish results in weight loss, porosity, crazing, and generally a reduction in flexibility. Degradation of the varnish can be detected by a decrease in dielectric strength, which is therefore used as the failure criterion for this test method.

    5.4 Electrical insulating varnishes undergo flexing in service due to vibration and thermal expansion. For this reason, this functional test includes flexing and elongation of the insulation. The electrodes used in this test method are designed to elongate the outer surface of the specimen 2 % with respect to the neutral axis of the base fiber while being tested for dielectric breakdown.

    1. Scope

    1.1 This test method covers the determination of the relative thermal endurance of flexible electrical insulating varnishes by determining the time necessary at elevated temperatures to decrease the dielectric breakdown of the varnish to an arbitrarily selected value when applied to a standard glass fiber fabric.

    1.2 This test method does not apply to varnishes that lose a high percentage of their dielectric breakdown voltage when flexed before elevated temperature exposure as prescribed in the screening test (Section 9). Examples of such varnishes are those used for high speed armatures and laminated structures. Also, this test method is not applicable to varnishes which distort sufficiently during thermal elevated temperature exposure so that they cannot be tested using the curved electrode assembly.

    1.3 Thermal endurance is expressed in terms of a temperature index.

    1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

    Note 1: There is no equivalent IEC or ISO standard.

    1.5 This 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 appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. For specific hazard statements, see Section 7.

    1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.


    2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.

    ASTM Standards

    D149 Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials at Commercial Power Frequencies

    D374/D374M Test Methods for Thickness of Solid Electrical Insulation

    D580/D580M Specification for Greige Woven Glass Tapes and Webbings

    D618 Practice for Conditioning Plastics for Testing

    D1346 Test Method for Testing Electrical Insulating Varnishes for 180 C and Above

    D1711 Terminology Relating to Electrical Insulation

    D2307 Test Method for Thermal Endurance of Film-Insulated Round Magnet Wire

    D2518 Specification for Woven Glass Fabrics for Electrical Insulation

    D5423 Specification for Forced-Convection Laboratory Ovens for Evaluation of Electrical Insulation


    ICS Code

    ICS Number Code 29.035.60 (Varnished fabrics)

    UNSPSC Code

    UNSPSC Code 31211707(Varnishes)


    Referencing This Standard
    Link Here
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    DOI: 10.1520/D1932-19

    Citation Format

    ASTM D1932-19, Standard Test Method for Thermal Endurance of Flexible Electrical Insulating Varnishes, ASTM International, West Conshohocken, PA, 2019, www.astm.org

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