Characterization of Electric Discharge-Induced EMI

EMI generated by corona and surface discharges were measured in an EMC chamber. Corona discharges (CDs) were generated using a high-voltage AC source connected to a 120 cm long copper conductor with conductor diameters of 180 µm, 850 µm, and 2650 µm. SDs were generated using two cylindrical stainless steel electrodes with a glass insulator between them. The diameter of the stainless steel electrodes is 53 mm, and the height of the cylinder is 58 mm. The cylindrical electrodes have rounded edges to eliminate partial discharges.
The applied AC voltage ranged from 5 kV to 55 kV with a voltage step of 5 kV for CDs and from 2 kV to 20 kV with a step of 2 kV for surface discharges (SDs). The frequency spectra of CDs (SDs) after application of high voltage (HV) were measured by a spectrum analyzer (SA) in the frequency range from 30 MHz to 1 GHz with a calibrated EMC antenna. A peak detector was used to measure the frequency response of EMI CDs and SDs, and the resulting value is the average of twenty sweeps. The distance of the CDs and SDs source from the EMC antenna is 2.35 m, and the height of the antenna above the floor is 1.3 m. The EMI generated by CD and SD is measured separately for horizontal and vertical polarization. The EMI values ​​represent the electric field strength in dBµV/m.
The frequency spectrum reveals the local maxima of EMI emission CDs and SDs, which increase with the increasing value of applied AC high voltage. EMI amplitudes are not equal at local maxima for horizontally and vertically polarized electromagnetic waves. Horizontally polarized EMI exhibited a sharp increase with increasing voltage, reaching saturation at 55 kV, while vertically polarized EMI showed a more gradual exponential trend. SDs' EMI values are 10 dB to 20 dB higher than CDs', depending on the diameter of the copper conductor and the local EMI maximum. The increase in EMI SDs with increasing voltage has an exponential trend, while EMI CDs show a more gradual increase after reaching the inception voltage.
CDs and SDs represent an undesirable source of EMI for radio communication technologies at some frequencies. SDs, by their nature and magnitude, appear to be a more intense source of EMI in the 30 MHz to 400 MHz band.