Evaluation of Insulation Performance in Oil-Immersed Power Equipment Under Low Temperatures

To investigate the dielectric properties of oil-impregnated paper and transformer oil at low temperature conditions that effect the performance of power equipment situated at cold climatic zone. This research focuses on the effects of aging and temperature on the dielectric properties, moisture content, viscosity, conductivity of transformer oil and oil-paper insulation. Frequency Domain Spectroscopy method is used to determine dielectric loss, and real and imaginary permittivity over a temperature range of 10°C to -40°C, where the results indicate that aging drastically changes the dielectric response, increases dielectric losses and lowers molecular mobility at low temperatures. The findings showed that aging significantly alters the dielectric response, increases dielectric losses, and reduces molecular mobility specifically at low temperatures. The Cole-Cole model was employed to assess the dielectric relaxation model, but its accuracy was compromised at extremely low temperatures. The effect of low temperatures on transformer oil viscosity and DC conductivity also considered. Which shows the viscosity increases exponentially as the temperature decreased, leading to reduced conductivity. The temperature dependence of viscosity and conductivity was well described by the Arrhenius and Vogel Fulcher Tammann models. These findings highlight the critical need to assess the aging and temperature effects on insulating materials to ensure the reliability of power equipment under harsh operating conditions.