A criterion for UV detection of AC corona inception in a rod-plane air gap

This paper presents a series of experimental investigations involving the use of ultraviolet (UV) detection of corona discharges from a rod-plane air gap subjected to high AC voltages. To establish a criterion to identify the beginning of dangerous levels of corona discharges, using UV images, coronas from air gaps of various lengths were observed using a UV camera located at a fixed position, and coronas from an air gap with a fixed gap length were recorded from various observation distances. The corresponding UV images were then analyzed via an image-processing method developed by the authors. In the processed UV images, the area ratio of the UV discharge zone to the total region of interest was defined as an indicator of the intensity of corona discharges. Test results revealed that for different corona discharges, their developing stages could be uniquely described using attenuation in the intensity of the corona UV image with observation distance. Based on the findings, a criterion is proposed for the detection of corona inception. An onsite application of the proposed method and criterion is provided and discussed.