Diagnosis of Partial Discharges in High Voltage Oil-Filled Bushings Based on the Periodic Tests Results

A comparative analysis of the reliability of partial discharge recognition using the periodic test results performed at low voltage and the dissolved in oil gas analysis for 24 high voltage bushings of sealed design is given. It was found that the periodic test results allowed to recognise partial discharges in 6 bushings out of 24, and the dissolved gas analysis results allowed to recognise partial discharges in 23 bushings. The correlation analysis performed has shown that in the development of partial discharges a significant statistical relationship has been revealed between gases characteristic of partial discharges (hydrogen, methane and ethane), as well as between these gases and the values of the dielectric loss tangent of the main bushings insulation. Based on the analysis of the trends in the gases indicators over time, it is demonstrated that the development of partial discharges does not always lead to a significant change in the values of the basic insulation of the gases, but the nature of the gas concentration dependences changes significantly.