A novel combined in-oil PD sensor with AE and UHF methods for PD detection in transformer, part 2: experimental verification

A combined in-oil partial discharges (PD) sensor with acoustical emission (AE) and ultra high frequency (UHF) methods for PD detection in transformer is designed and developed, according to the disadvantages and advantages of electromagnetic and acoustic PD measurements shown in IEC TS 62478 Edition 1.0 2016–08. It is formed by placing an AE sensor inside the end part of UHF probe to fit for the transformer oil valve, which works independently of each other with two output channels for AE and UHF PD signals measurements. Test results of a 110 kV transformer with built-in tip, suspension and surface insulation defects show that the combined UHF/AE in-oil PD sensor designed and developed can effectively detect the electromagnetic wave and ultrasonic signal with a specific time difference $\Delta\mathbf{t}$ generated by the weak discharges in the transformer oil, which provides a new mixed electromagnetic and acoustic method for PD measurements of transformer.