UHF PD Online Monitoring of Huge-Size Transformers and Data Analysis

It is widely accepted that failures due to insulation defects are often preceded by some form of PD activities in HV equipments. This paper describes practical application of the UHF PD detection on a new oil-immersed power transformer. An internal UHF sensor was designed and installed to the transformer for insulation condition assessment. As the frequency band of this UHF sensor was 300~1500 MHz, envelope detection technique was used to extract UHF signals excited from PD sources inside the transformer. The results of MATLAB simulation and experimental measurements have shown that UHF PD signals can be effectively extracted by this method. Using the monitoring system established in this paper, typical UHF PD patterns were recorded during PD acceptance test, which reveal that UHF PD measurements can detect small level of discharges with good sensitivity. Finally, online monitoring data including strong external disturbances such as lightning strikes, switching operation pulses was studied.