Effect of Zeolite Addition on Partial Discharge and Dielectric Behavior of Thermally Aged Synthetic Ester Fluid Under External Magnetic Field

In recent times, ester based liquids have met high standards and are being considered as potential alternatives over mineral oil transformer insulation. This paper investigates the effect of adding micro-porous zeolite to the thermally aged synthetic ester oil (SEO) to evaluate its electrical performance under the influence of external local magnetic field variation from 0 mT to 165 mT. It is observed that the Corona Inception Voltage (CIV) and Particle Levitation Voltage (PLV) have a declining tendency with ageing, in the presence of magnetic field. Under the influence of magnetic flux density (
$\simeq 160$
mT), the detected UHF signal was dominant at low frequencies (400 MHz - 900 MHz). The UHF voltage signals peak-to-peak magnitude demonstrates that the discharge magnitude increases with increased ageing duration. Further, it was observed that the addition of zeolite in the synthetic ester liquid tends to improve the electrical performance of the aged oil. The fluorescence spectroscopic analysis shows a shift of the fluorescence maxima together with increased intensity in samples with zeolite as compared to the samples without zeolite addition, which shows a relatively lower concentration of the polar contamination. The frequency dielectric spectroscopy also confirms that synthetic ester specimens showed improved dielectric properties after the zeolite treatment.