171 / 2018-08-25 21:56:48

A Model to Describe the Voltage-Current Characteristics in Nonlinear Dielectrics

nonlinear dielectrics,electrical properties,conductivity,high order polarization

With the development of material science, polymer dielectrics have become the main materials in modern electrical insulation. The conductivity and the permittivity (or relative permittivity, which is also called dielectric constant) are important electrical properties of dielectric materials. The nonlinear dielectrics is a kind of dielectrics whose conductivity or permittivity depending on the applied electric field. And because of its outstanding function of making electric field distribute uniformly and keeping the stability of the whole insulating structure, the nonlinear dielectrics is also called "smart insulating material". Up till now, there have been some models to describe the conductive process in solid dielectrics such as hopping theory, space charge limited electrical conduction, the Poole-Frenkel model and so on. And the permittivity is generally regarded as being independent of the filed strength in most insulation materials. But some experiment results we acquired do not consist with the calculation in theory if the permittivity is considered to be independent of the filed strength.
Nonlinear dielectrics is often achieved by filling nonlinear filler in polymer matrix. In this paper, ZnO fillers/LDPE composite samples are prepared to investigate the V-I characters. A model consists of three current components that conductive current, high frequency polarization current and relaxation current is proposed to describe the Voltage-Current(V-I) characters of the prepared samples. The high frequency polarization current is determined by the optical polarization. The conductive current lies on the conductivity and the relaxation current depends on the electrical susceptibility. The conductivity and the electrical relaxation susceptibility in our model are polynomial of applied electric field. At present, we just consider the second order conductivity and polarization related to the quadratic terms in electric field. Different voltage forms are applied to the samples, respectively, such as AC voltage, triangular voltage and trapezoidal voltage which are created by the combination of an arbitrary signal generator and a high voltage amplifier. The current data is collected by the oscilloscope.
The results calculated by the model proposed in this paper can coincide with the experimental V-I character well. This can verify that our model is proper to describe the V-I characteristics and the V-I performance in nonlinear dielectrics is regulated by the applied electric field to some degree. When the applied filed increase, the current curve will distort more obviously. That is because the quadratic terms in electric field will play a notable component. According to this feature we can speculate that the higher order conductivity and polarization will appear when the field is high enough. The changing rate of the applied electric field will also affect the higher order conductivity and the polarization. The reason for this phenomenon is similar to that explained above. In a nutshell, the model proposed in this paper is able to explain the voltage-current characters and. In the future work, more deeper physical reasons related to these phenomenon will be studied, which can help people to understand the nonlinear dielectrics more clearly.