Deepening of the Study of Corona Discharges by Recent Advances of Electrical and Optical Measurement Techniques

The basic properties and applications of corona discharges have been studied for a long time. The fundamental research covers a wide range of discharge parameters, including corona starting voltage, current values and its distribution, several modes depending on the applied voltage polarity (glow and streamer for positive coronas, Trichel pulse and pulseless glow for negative coronas), ionic wind induced EHD gas flow, and ozone levels. In recent years, we have developed the methodology for the investigation of these all characteristics under repetitive ramp and triangular voltage applications. In particular, recent advances in measurement methods have led to an in-depth the understanding of corona discharges. Here, a typical needle-to-plate electrode system is used as the discharge electrode. The electrical characteristics of both positive and negative corona discharges (e.g., the corona onset voltage, the voltage at which the corona discharge transfers its mode, the appearance of corona discharge modes, the average current-voltage (I-V) characteristics, and the corona discharge hysteresis) is automatically investigated by repetitive ramp and triangular voltages generated with a high voltage amplifier with a function generator. Optical study makes clear the corona emission by full color observation with optical emission spectroscopy. Furthermore, real color corona imaging is performed by using a highly sensitive digital camera equipped with a zoom lens. Also the gas velocity flow field generated by ionic wind is observed by Schlieren technique. These extensive research opportunities will further advance our knowledge of corona discharges. This paper presents a broad overview of the latest corona discharge measurement technology we have developed.