ASTM D150-22

5.1?PermittivityInsulating materials are used in general in two distinct ways, (1) to support and insulate components of an electrical network from each other and from ground, and (5.2?AC LossFor both cases (as electrical insulation and as capacitor dielectric) the ac loss generally needs to be small, both in order to reduce the heating of the material and to minimize its effect on the rest of the network. In high frequency applications, a low value of loss index is particularly desirable, since for a given value of loss index, the dielectric loss increases directly with frequency. In certain dielectric configurations such as are used in terminating bushings and cables for test, an increased loss, usually obtained from increased conductivity, is sometimes introduced to control the voltage gradient. In comparisons of materials having approximately the same permittivity or in the use of any material under such conditions that its permittivity remains essentially constant, it is potentially useful to consider also dissipation factor, power factor, phase angle, or loss angle. Factors affecting ac loss are discussed in Appendix X3.

5.3?CorrelationWhen adequate correlating data are available, dissipation factor or power factor are useful to indicate the characteristics of a material in other respects such as dielectric breakdown, moisture content, degree of cure, and deterioration from any cause. However, it is possible that deterioration due to thermal aging will not affect dissipation factor unless the material is subsequently exposed to moisture. While the initial value of dissipation factor is important, the change in dissipation factor with aging is often much more significant.

5.4?Capacitance is the ratio of a quantity, 5.5?Dissipation factor ((D), (loss tangent), (tan ?)) is the ratio of the loss index (?") to the relative permittivity (?') which is equal to the tangent of its loss angle (?) or the cotangent of its phase angle (?) (see Fig. 1 and Fig. 2).

5.6?Loss angle ((phase defect angle), (?)) is the angle whose tangent is the dissipation factor or arctan ?"/?' or whose cotangent is the phase angle.

5.7?Loss index (?" (?<sub>5.7.1?The loss index is expressed as:


.</sub>

When the power loss is in watts, the applied voltage is in volts per centimeter, the frequency is in hertz, the volume is the cubic centimeters to which the voltage is applied, the constant has the value of 5.556 ? 10^?13.

5.8?Phase angle (?) is the angle whose cotangent is the dissipation factor, arccot ?"/?' and is also the angular difference in the phase between the sinusoidal alternating voltage applied to a dielectric and the component of the resulting current having the same frequency as the voltage.

5.9?Power factor (PF) is the ratio of the power in watts, 5.9.1?Power factor is expressed as the cosine of the phase angle ? (or the sine of the loss angle ?).

When the dissipation factor is less than 0.1, the power factor differs from the dissipation factor by less than 0.5 %. Their exact relationship is found from the following:

5.10?Relative permittivity ((relative dielectric constant) (SIC) ?'(?_r)) is the real part of the relative complex permittivity. It is also the ratio of the equivalent parallel capacitance, C_p, of a given configuration of electrodes with a material as a dielectric to the capacitance, C_?, of the same configuration of electrodes with vacuum (or air for most practical purposes) as the dielectric: