Study on electromagnetic radiation of some kinds of typical partial discharge

Partial Discharge (PD), being the early manifestation of insulation faults within gas insulated substation (GIS), poses a potential threat to the normal operation of GIS. As a powerful diagnostic method, the ultra-high-frequency (UHF) PD detection system has many attractive advantages, such as good anti-interference, high efficiency of on-line detection, and strong ability of locating PD. So that it has been well accepted as the main electromagnetic method of detecting PD in GIS. But there are still some problems that need to be studied in the identification system including partial discharge type and developing stage. By using the high stability and high repetition experimental models of the needle-to-plate corona discharge, the surface discharge and the suspended discharge, the currents and its corresponding electromagnetic radiation of typical PD were measured. The results show that the radiation spectrum of corona discharge is quite low, the spectrum of surface discharge gathers around 125 MHz, and the spectrum of suspended discharge is wider, whose range is quite near around 25MHz, 75MHz and 125 MHz. For the corona discharge, there exists a segmentation phenomenon in the positive polarity current rising edge during the long brush discharge stage, and results in the segmentation phenomenon in electromagnetic radiation waveforms. The phenomenon is estimated by the analytical formula of electromagnetic radiation produced by a current pulse based on the dipole model. The part of quasistatic field dominated by i(t) and the part of radiation field dominated by di(t)/dt will determine the peak of radiation waveforms together. The above research has a good guidance to the relevant identification system which monitors PD.