What is dielectric loss?

Everyone knows that a dielectric is a material that prevents electric current from passing through. There are a huge number of such materials and substances. In addition to their essential properties, they possess a number of other additional properties. Such features include dielectric loss - the energy that is dissipated in a material under the influence of electric fields. Due to this energy, the material heats up, as a result of which its thermal destruction and other adverse effects can occur. Next, we consider what dielectric losses in dielectrics are, how they arise and with what are measured.

Content:

Calculation Method
Types of losses
In the gases
In solids
In liquids
Instrumentation Overview

Calculation Method

Dielectric losses require measurement using a rather complicated calculation system. This system consists of several stages. First of all, it is necessary to calculate the power that a dielectric possesses and what dissipates in it at an alternating voltage. It is determined by the formula:

Pa = U * Ia

The figure below shows the diagrams of the series (a) and parallel (b) connection of the capacitor and active resistance, as well as vector diagrams of the currents in them.

Thus, it is possible to determine the active current, the calculation formula of which will be as follows:

The second value is the tangent of the angle of the vector of the full value of the current to its capacity. This angle is also called the dielectric loss angle. Ic is the dielectric capacitance.

Drawing conclusions from the data obtained, a more detailed formula for calculating power is obtained:

In this case, the current is calculated by the formula: angular frequency * capacitor capacitance. Based on the formulas provided, you can calculate the power as follows:

Based on this formula, it can be seen on what factors the quality and reliability of such a device as a dielectric depend. If you look at the graph, you can see that the properties increase with decreasing angle.

Types of losses

In the gases

In gaseous substances, the electrical conductivity is small and, as a result, dielectric losses will also be insignificant. With the polarization of gas molecules, nothing happens. In this case, the so-called ionization curve is used.

This subordination indicates that with increasing voltage, the angle will also increase. And this means that there is a gas inclusion in the insulation. In the case of large ionization, gas loss will be significant and as a result - heating and destruction of insulation.

Therefore, when making insulation, it is very important to take into account the fact that there should be no gas inclusions. For this, special processing is used. Its essence is as follows: insulation is dried in a vacuum. Then the pores are filled with a compound that is under pressure and then break-in occurs.

As a result of ionization, oxides of nitrogen and ozone appear, which destroy the insulation.At times when the ionization effect occurs on a plot of uneven fields, this during transmission leads to a decrease in the efficiency.

In solids

A solid dielectric has certain characteristics, such as composition, structure, and polarization, which lead to dielectric losses. For example, they are absent in sulfur, paraffin or polystyrene; therefore, these substances are widely used as a high-frequency dielectric.

Quartz, salt, and mica have through conductivity; therefore, they are characterized by an insignificant amount of these losses.

Dielectric losses do not depend on the frequency (a), will decrease along with the field frequency according to the hyperbolic law. But with temperature they depend directly on the exponential law (b).

A crystalline dielectric such as ceramic or marble has a characteristic indicator of this value. This is due to the fact that they contain semiconductor impurities. Such a material has a distinctive property: dielectric losses are directly related to the environment and its conditions. Therefore, depending on the change of factors that surround the dielectric, the value of one material may vary.

In liquids

In this case, losses are directly related to the composition of the material. If there are no impurities in the liquids, then it will be neutral and the loss will tend to zero, since the electrical conductivity is low.

Liquids with polarity or with the presence of impurities are used for certain technical purposes, since their dielectric loss will be much higher. This is due to the fact that such liquids have their own special properties, for example, viscosity. And since they are determined by dipole polarization, these liquids are called dipole polarizations. With increasing viscosity, dielectric losses increase.

In addition, liquids have a certain dependence of losses on temperature. When the temperature regime increases, the tangent of the angle also increases to a maximum value. Then it drops to the minimum value and increases again. This is because the conductivity changes under the influence of temperature.

Instrumentation Overview

There are special instruments for measuring losses. These include the IPI-10 device, a Tettex device, and dielectrics of solid and liquid substances are studied with it. An automated installation called "Tangent - 3M" is used to determine the tangent of the angle in liquid dielectrics (pictured below). Also use meter "Ш2 - 12ТМ".