Understanding incipient discharge characteristics in nano ester oil under AC/DC voltages adopting UHF technique

Ester Oil has been most commonly suggested as an alternative transformer oil insulation owing to its higher biodegradability and excellent dielectric and thermal properties. Development of nanofluids based on ester oil is considered as the future of insulating fluids which hold great potential to enhance the design aspect of high voltage apparatus. In the current study effect of SiO2 on dielectric properties of natural ester oil has been studied. Based on various electrical analysis, an attempt has been made to identify the optimum concentration of nanoparticles in terms of volume concentration. In order to enhance dispersion and improve surface properties, CTAB has been chosen as a surfactant and its optimum concentration with respect to nanofluid has been established. Corona Inception Voltage (CIV) results indicate that beyond a certain value, addition of nanoparticles can degrade the dielectric properties of oil. These results are further confirmed by testing the Levitation Voltage of the particle in the electrode gap. It is realized that incipient discharges due to corona/particle movement can radiate electro-magnetic waves with its frequency lying in Ultra High Frequency (UHF) signal range. It is observed that the bandwidth of the radiated signal lies in the frequency range of 0.7-2 GHz, with its dominant frequency at 0.9 GHz. It was observed that the number of discharges caused due to corona/particle movement are less for the identified optimum concentration of nano SiO2 in transformer oil. It has been observed that the number of discharges is higher for AC voltage than DC voltage, due to particle movement.