Investigation of Temperature Effect on Conductance Characteristics of Transformer Oil-based Nanofluids

Abstract

Adding some nanoparticles to the transformer oil can improve its heat exchange properties as well as its dielectric withstanding characteristics, which has attract more and more attentions in the world. The conductance characteristics of transformer oil-based nanofluids (TNFs), especially at different temperatures, will help to understand the modification theory. The charge carrier transport processes at different electric fields can be divided into three stages: Ohmic, tunneling and space charge limited current (SCLC), respectively. In Ohmic stage at a very low field, the addition of nanoparticles increases the carrier number density, thus the conduction current is increased. In tunneling stage at medium to high electric field strengths, the main charge carriers in the transformer oil change from ions and colloidal particles to electrons emitted from the electrodes. The addition of nanoparticles increases the barrier thickness at the metal-liquid interface, which reduces the amount of electrons passing through the interface region. Therefore, the field strength required for electron transport is enhanced, and the dielectric strength is improved. In the space charge limited current stage at a very high electric field, the large trap density of TNFs lowers the carrier mobility, suppressing the discharge. In addition, as the temperature increases, the accelerated movement of the carriers increases the conduction current in the transformer oil. However, the electron tunneling process in the tunneling stage is little affected by the change in temperature.