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.

本研究在电磁兼容（EMC, Electromagnetic Compatibility）暗室中，测量了电晕放电与沿面放电产生的电磁干扰（EMI, Electromagnetic Interference）。电晕放电（CD, Corona Discharges）采用高压交流电源激发，该电源连接至长度为120 cm的铜导体，铜导体直径分别设置为180 µm、850 µm与2650 µm。沿面放电（SD, Surface Discharges）则通过两枚圆柱状不锈钢电极实现，电极间夹有玻璃绝缘子；不锈钢电极直径为53 mm，圆柱高度为58 mm，且电极边缘做圆角处理以避免产生额外局部放电。
针对电晕放电，施加的交流电压范围为5 kV至55 kV，电压步长为5 kV；针对沿面放电，交流电压范围为2 kV至20 kV，步长为2 kV。施加高压（HV, High Voltage）后，通过经校准的电磁兼容天线与频谱分析仪（SA, Spectrum Analyzer），在30 MHz至1 GHz的频率范围内，采集电晕放电与沿面放电的频率谱数据。采用峰值检波器测量两类放电的电磁干扰频率响应，最终结果为20次扫描的平均值。放电源与电磁兼容天线的间距为2.35 m，天线距地面高度为1.3 m。本数据集分别针对水平极化与垂直极化两种模式，单独测量电晕放电与沿面放电产生的电磁干扰，测量值以分贝微伏每米（dBµV/m）为单位的电场强度表示。
频率谱分析显示，电晕放电与沿面放电的电磁干扰发射存在局部峰值，且峰值随施加的交流高压升高而增大。水平极化与垂直极化电磁波的局部峰值处电磁干扰幅值并不一致：水平极化电磁干扰随电压升高呈陡增趋势，并在55 kV时达到饱和；而垂直极化电磁干扰则呈现更为平缓的指数增长趋势。沿面放电的电磁干扰幅值较电晕放电高10 dB至20 dB，具体差值取决于铜导体直径与电磁干扰局部峰值的位置。沿面放电的电磁干扰幅值随电压升高呈指数增长，而电晕放电则在达到起晕电压后呈现更为平缓的增长态势。
在部分频率下，电晕放电与沿面放电会对无线电通信技术造成不良电磁干扰。从特性与幅值来看，沿面放电在30 MHz至400 MHz频段内属于强度更高的电磁干扰源。