AC conductivity measurements of liquid-solid insulation of power transformers with high water content

Abstract

• Electron tunneling takes place between neighboring potential wells, water nano-drops. • In materials there are two types of hopping conductivity. • Activation energy of relaxation times at growth stages in σ( f ) plots are similar. • Composition and structure nanoparticles, between which electrons tunnel, are similar. The paper investigated the influence of temperature on the frequency dependence of the conductivity of cellulose-ester insulation of power transformers containing nano-drops of water. It was observed that in the insulation containing nano-drops of water on the σ( f ) dependence two sections of conductivity increase occur. It was found that the state of the frequency dependence of conductivity is affected simultaneously by the temperature dependence of conductivity and the temperature dependence of dipole relaxation time. Activation energies for conductivity and relaxation times were determined, the values of which are the same for both stages of the conductivity increase. This means that the structure of water nanoparticles, between which electrons tunnel, is the same for both stages of σ( f ) growth. The occurrence of the two growth stages on the frequency dependence of conductivity is associated with differences in distances between adjacent nanoparticles and the associated relaxation times.