Investigation of DC corona discharge properties using UHF method

Partial Discharge (PD) measurement is well known as powerful method to identify the condition of high-voltage insulation. This paper investigates the properties of the ultra-high frequency (UHF) electromagnetic (EM) wave emanating from the air discharge (corona) under high voltage DC source. By applying both positive and negative high voltage DC ranging up to 135 kV, a rod antenna and a horn antenna were used as UHF sensors to detect any EM wave emission from PD activity and breakdown in air insulation. The experiment results show that typical PD emission signals under positive DC have higher voltage amplitude and wider burst width pulses than the typical PD emission signals under negative DC. Moreover, it is found that the first-peak of EM wave emission under positive DC has negative polarity while under negative DC has positive polarity. In addition, FFT analysis shows that this typical air discharge has dominant amplitude in frequency bands below 250MHz. Another significant result of this experiment is the inability of the horn antenna to detect the EM emission from air discharge.