Dielectric spectroscopy techniques

Overview

We analyze the changes experienced by the dielectric materials, to be subjected to any physical or chemical treatment (physical aging, crystallization, oxidation ...) from the behavior of electrical conduction mechanisms. These conductive mechanisms, dipoles and free charges, are activated to polarize the material at high temperatures, and the situation achieved is "frozen" by cooling the material.

The monitoring of the state to which the material is made by applying the reverse process followed in the previous section, heating the material. The scheme explained is called the current thermo-stimulated technique. There are other techniques that also allow value through the perspective of an electrical insulating material situation.

THE TECHNIQUE OF THERMALLY STIMULATED CURRENTS (TSDC)

Formation of the electretMostrar forma romanizada

Initially, the TSDC technique involves placing the sample between two electrodes, as a sandwich, at high temperatures, applying an electric field and cooling the system with the applied field. The field causes orientation of permanent dipoles or induced, and movement of free charge located inside the volume of the material. The field can also cause deposition effects of surface charge (corona), or cause injection of free carriers on the surface or on the internal volume of the material.

Thermo Stimulation

When the temperature reaches room temperature, and we remove the applied field, the material is charged forming an electret, and conduction mechanisms are frozen and conditioned by prior treatment done. The Thermo Stimulation, based on controlled warming of the material, causes that the system electrically altered recover the balance rapidly. This is because with increasing temperature the material increases their energy, frozen carrier are activated and recover balance. Mostrar forma romanizadaIn this situation, and in the process of heat swept, it’s possible to record a displacement current j (T) that can give different peak current, reflecting the spectrum of the material. The peaks are associated with different dipolar groups activated or with free electric charges trapped in the process of polarization. The system is very sensitive and responds to any treatment that affects the structure of molecular materials.

TECHINQUE FOR MEASURING THE SURFACE CHARGE DEPOSITED ON INSULATION

This technique reveals the charge of a material. The tracking is done at room temperature using a compensation method that creates the field of trapped charge. The process is carried out following the fall of the potential burden placed and allows us to determine the amount of charge that accumulates the sample. In particular if you charge the material surface can track the trapped surface charge.

TECHNICAL ANALYSIS OF ELECTRIC-DYNAMICS

It is the oldest technique. The application of alternate fields to the isolates, the polarization and displacement are phased out. This delay is due to mechanisms that are conductive to keep the frequencies applied. Both the dipoles and free charges are subject to these conditions and this delay reflected in the permittivity (real and complex) and other related parameters (model electrical conductivity, impedance ...). It is usually record the variations of permittivities (real and imaginary) as a function of frequency at different fixed temperatures, or follow the behavior of these parameters depending on temperature. Both curves are obtained spectrum of the material. Today we have seen that TSDC spectrum and the DEA (permittivity versus temperature) are equivalent to frequencies of order of 10-4 Hz.

PULSE ELECTROACOUSTIC TECHNIQUE

This technique allows an analysis of the cumulative load distribution along the thickness of the insulation either during or polarization in the material already polarized by the piezoelectric transduction of sound waves that create burdens on receiving electrical impulses. The distribution allows obtaining the values of the total charge accumulated, using a suitable processing of data.