Electromagnetic spectrum caused by partial discharge in air under AC and DC voltage application

The authors measured electromagnetic spectrum radiated from partial discharge with a magnitude from 80 to 50,000 pC occurring in needle-plane electrodes. Experimental results showed that the gain of the electromagnetic wave decreased with increasing the distance from PD source in the frequency range from 35 to 50 MHz. The results were discussed in terms of a model assuming that electromagnetic wave radiation from a small dipole antenna simulates that from the PD source. Consequently, the distance characteristics of the signal gain proved to agree well with the theoretical calculation. An attempt was also made to measure separately the electromagnetic spectrum caused by positive and negative PD pulses. At the same time, PD pulses were measured with a computer-aided measuring system. The authors discussed the relationship between the PD statistical characteristics and the electromagnetic spectrum