Dielectric Constant and Dissipation Factor ASTM D150

Dielectric Constant (DC) and Dissipation Factor (DF) According in accordance with ASTM D150, IEC 60250

Dielectric Constant and Dissipation Factor are important properties used to evaluate the electrical insulation performance of materials. Dielectric Constant, also known as relative permittivity, is a measure of the ability of an insulating material to store electrical energy. The higher the dielectric constant, the more electrical energy can be stored by the material. Dissipation Factor, on the other hand, measures the efficiency of an insulating material in storing and releasing electrical energy. The lower the dissipation factor, the more efficient the material is at storing and releasing electrical energy.

Dielectric Constant is defined as the ratio of the capacitance induced by two metallic plates with an insulator between them to the capacitance of the same plates with air or a vacuum between them. This test can be conducted at different frequencies, usually between the 10Hz and 2MHz range, with the specific frequency determined by the customer.

To perform the test, a sample is placed between two metallic plates and capacitance is measured. A second run is measured without the specimen between the two electrodes. The ratio of these two values is the dielectric constant. It is important to note that the sample must be flat and larger than the 50mm (2 in) circular electrodes used for the measurement.

Dissipation Factor is defined as the reciprocal of the ratio between the insulating material's capacitive reactance to its resistance at a specified frequency. It measures the inefficiency of an insulating material. A lower dissipation factor indicates a more efficient insulating material.

The ASTM D150 and IEC 60250 standards provide guidelines for testing dielectric constant and dissipation factor. These standards specify the test conditions and the instruments required for accurate testing. The results obtained from these tests provide valuable information for selecting appropriate insulating materials for specific applications.

In general, when a material is used for strictly insulating purposes, it is better to have a lower dielectric constant. However, when a material is used in electric applications where high capacitance is needed, a higher dielectric constant is required.

Both Dielectric Constant and Dissipation Factor are important properties used to evaluate the electrical insulation performance of materials. The test procedure, as specified by ASTM D150 and IEC 60250, involves measuring the capacitance induced by two metallic plates with an insulator between them and comparing it to the capacitance of the same plates with air or a vacuum between them. The results obtained from these tests provide valuable information for selecting appropriate insulating materials for specific applications.

Test Method Summary for Measuring Capacitance, AC Resistance, and Permittivity of Specimens

I. Introduction:

This test method outlines the procedure to measure capacitance and AC resistance of a specimen. It provides guidance on selecting the right electrodes, equipment, measurement methodologies, and also offers directions to avoid or correct for capacitance errors.

II. Objective:

1. To calculate the relative permittivity of the specimen.

2. To determine the dissipation factor from measured values.

III. Test Equipment and Material:

1. Electrode systems

   • Contacting Electrodes: Electrode Materials, Metal Foil, Conducting Paint, Fired-On Silver, Sprayed Metal, Evaporated Metal, Liquid Metal, Rigid Metal, Water.

   • Non-Contacting Electrodes: Fixed Electrodes, Micrometer Electrodes, Fluid Displacement Methods.

2. Apparatus and Methods for Measuring Capacitance and A-C Loss: Frequency Direct and Substitution Methods, Two-Terminal Measurements, Three-Terminal Measurements, Fluid Displacement Methods, Accuracy considerations.

IV. Procedure:

1. Measure the capacitance and AC resistance of the specimen.

2. Calculate the relative permittivity:

   • Determine the specimen capacitance.

   • Calculate the vacuum capacitance using the provided electrode configuration.

   • Divide the specimen capacitance by the vacuum capacitance to get relative permittivity.

3. Calculate the dissipation factor using the measured values.

4. Use the method to:

   • Choose appropriate electrodes, equipment, and measurement methodologies.

   • Avoid or correct capacitance errors.

5. Take into consideration:

   • Fringing and stray capacitance.

   • Guarded electrodes.

   • Specimens' geometry.

   • Calculation of vacuum capacitance.

   • Corrections for edge, ground, and gap.