Analysis of Defects and Noise in Cast-Resin Transformers Using UHF Sensors

Cast-resin transformers have a risk of accidents leading to dielectric breakdown due to manufacturing defects such as cracks, thermal aging and voids. Detecting manufacturing defects and degradation in advance to prevent accidents is crucial in PD research. However, not only discharge caused by defects but also noise signals can be introduced through sensors. Therefore, it is necessary to study UPS noise that can be enter through sensors installed in cast-resin transformers. In this paper, the signals of defects and noise were measured and derived into PRPD patterns. The defects were selected as corona, surface and void discharges, and the noise sources were the rectifier and inverter of the UPS. It was confirmed that PRPD patterns differ according to the type of defect. Additionally, corona discharge showed pattern changes over time, while surface discharge extinguished. UPS noise varies depending on the operation of the rectifier and inverter. Through this, it is possible to distinguish between defects and noise.