ASTM D924 - 08

    Standard Test Method for Dissipation Factor (or Power Factor) and Relative Permittivity (Dielectric Constant) of Electrical Insulating Liquids

    Active Standard ASTM D924 | Developed by Subcommittee: D27.05

    Book of Standards Volume: 10.03


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    ASTM D924

    Significance and Use

    Dissipation Factor (or Power Factor)This is a measure of the dielectric losses in an electrical insulating liquid when used in an alternating electric field and of the energy dissipated as heat. A low dissipation factor or power factor indicates low ac dielectric losses. Dissipation factor or power factor may be useful as a means of quality control, and as an indication of changes in quality resulting from contamination and deterioration in service or as a result of handling.

    The loss characteristic is commonly measured in terms of dissipation factor (tangent of the loss angle) or of power factor (sine of the loss angle) and may be expressed as a decimal value or as a percentage. For decimal values up to 0.05, dissipation factor and power factor values are equal to each other within about one part in one thousand. In general, since the dissipation factor or power factor of insulating oils in good condition have decimal values below 0.005, the two measurements (terms) may be considered interchangeable.

    The exact relationship between dissipation factor (D) and power factor (PF) is given by the following equations:


    The reported value of D or PF may be expressed as a decimal value or as a percentage. For example:


    Relative Permittivity (Dielectric Constant)Insulating liquids are used in general either to insulate components of an electrical network from each other and from ground, alone or in combination with solid insulating materials, or to function as the dielectric of a capacitor. For the first use, a low value of relative permittivity is often desirable in order to have the capacitance be as small as possible, consistent with acceptable chemical and heat transfer properties. However, an intermediate value of relative permittivity may sometimes be advantageous in achieving a better voltage distribution of a-c electric fields between the liquid and solid insulating materials with which the liquid may be in series. When used as the dielectric in a capacitor, it is desirable to have a higher value of relative permittivity so the physical size of the capacitor may be as small as possible.

    Theory relating to dielectric measurement techniques and to sources of dielectric loss is given in Test Methods D 150.

    1. Scope

    1.1 This test method describes testing of new electrical insulating liquids as well as liquids in service or subsequent to service in cables, transformers, oil circuit breakers, and other electrical apparatus.

    1.2 This test method provides a procedure for making referee tests at a commercial frequency of between 45 and 65 Hz.

    1.3 Where it is desired to make routine determinations requiring less accuracy, certain modifications to this test method are permitted as described in Sections 16 to 24.

    1.4 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 and health practices and to determine the applicability of regulatory limitations prior to use. Specific warnings are given in 11.3.3.

    1.5 Mercury has been designated by the EPA and many state agencies as a hazardous material that can cause nervous system, kidney and liver damage. Mercury, or its vapor, may be hazardous to health and corrosive to materials. Caution should be taken when handling mercury and mercury containing products. See the applicable product Material Safety Data Sheet (MSDS) for details and the EPA's website: http://www.epa.gov/mercury/faq.htm for additional information. Users should be aware that selling mercury and/or mercury containing products into your state may be prohibited by state law.


    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

    D150 Test Methods for AC Loss Characteristics and Permittivity (Dielectric Constant) of Solid Electrical Insulation

    D923 Practices for Sampling Electrical Insulating Liquids

    D2864 Terminology Relating to Electrical Insulating Liquids and Gases

    D2865 Practice for Calibration of Standards and Equipment for Electrical Insulating Materials Testing

    E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method


    ICS Code

    ICS Number Code 29.040.10 (Insulating oils)

    UNSPSC Code

    UNSPSC Code 15121505(Transformer oil or insulating oil)


    DOI: 10.1520/D0924-08

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