Experimental investigation of the effect of nano particles on the breakdown strength of transformer liquids by harmonic current analysis

The different dielectric strength behaviour that occurs when the metal particles broken off from the iron core and copper windings penetrate into the transformer oil needs to be examined in detail. These metals, which are in oxide form, generally penetrate into the liquid dielectric material in the form of circular powders in nanometre size. Copper oxide (CuO) and iron oxide (Fe3O4) components change the characteristics of leakage currents in the oil by affecting the ionization process in different directions under electric field stress. These nano powders, which orientate differently in both polarities under AC Voltage, can generate current in different frequency components except from grid frequency. In this study, the dielectric behaviour of mineral oil, natural ester and synthetic ester was investigated under the influence of nano metal particles. In accordance with ASTM D1816-12 and ASTM D877/87M-19 standards, the mentioned liquid dielectrics were tested with 1 mm electrode gap using disc and VDE type electrodes. The harmonic values between 0 and 1 kHz frequency band were calculated from the current signals obtained over the voltage divider. By calculating the total distortion effect of these harmonics, the liquids were compared amongst themselves in terms of dielectric strength. In addition, FTIR application was carried out for the analysis of functional groups in the structures of liquids. According to the FTIR analysis, it is shown that the difference of functional groups in the liquid dielectric also affected the dielectric strength. It has been demonstrated that the bond structure in the synthetic ester liquid is more resistant to electric field stresses.