Dielectric losses in dielectrics

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 also have a number of other additional ones. This feature includes dielectric loss - energy that is dissipated in a material under the influence of electric fields. This energy heats up the material, resulting in thermal degradation and other adverse effects. Next, we will consider what dielectric losses in dielectrics are, how they arise and how they are measured.

Calculation method

Dielectric losses require measurement using a rather complex rendering system. This system consists of several stages. First of all, it is necessary to calculate the power that the dielectric has and what is dissipated in it with an alternating voltage. It is determined by the formula:

Pa = U * Ia

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

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

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

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

In this case, the current is calculated by the formula: angular frequency * 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.

Loss types

In gases

In gaseous substances, the electrical conductivity is small and, as a result, dielectric losses will also be negligible. When gas molecules are polarized, nothing happens. In this case, the so-called ionization curve is applied.

This subordination indicates that with increasing voltage, the angle will also increase. This means that there is a gas inclusion in the insulation. In the case of high ionization, the loss of gas will be significant and as a result - heating and destruction of the 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: the insulation is dried in a vacuum. Then the pores are filled with a compound, which is under pressure, and then running-in takes place.

As a result of ionization, oxides of nitrogen and ozone appear, which destroy the insulation. At the moments when the ionization effect occurs in the area 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, that 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 electrical conductivity, so they are characterized by an insignificant amount of these losses.

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

Crystalline dielectric such as ceramics or marble has a characteristic value for 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 change.

In liquids

In this case, losses are directly related to the composition of the material. If there are no impurities in liquids, then it will be neutral and losses 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 losses will be much higher. This is due to the fact that such fluids have their own special properties, for example, viscosity. And since they are established by dipole polarization, these liquids are called dipole. With increasing viscosity, dielectric losses increase.

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

Overview of measuring instruments

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

Finally, we recommend watching a useful video on the topic:

Now you know what dielectric losses in dielectrics are, how they are calculated and measured. We hope the information provided was useful to you!

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