An Online UHF PD Monitoring System for Power Transformer and Its Applications

It is widely accepted that failure due to insulation defects are often preceded by some form of partial discharge (PD) activity in high voltage (HV) equipments. This study describes industrial application of ultra high frequency (UHF) PD detection technique on large oil-immersed power transformers. To suppress external interference internal UHF sensors were designed and successfully installed to 4 power transformers for their insulation assessment. As the frequency band of the UHF sensor was 500-1500 MHz, envelope detection technique was employed to extract UHF signals. Typical UHF PD patterns were recorded during PD acceptance test using the monitoring system. The results reveal that UHF PD measurements can detect small level of discharges with good sensitivity. Finally, the influence of external impact pulses such as lightning strike pulses, switching operation pulses was studied as well. The system has been put into service to 4 power transformers.