On spectral characteristics and chemical product analysis of AC discharge plasma under atmospheric pressure

Abstract Tip defects in power equipment components generate non-uniform electric fields that induce sustained partial discharge (PD). Previous studies on spectral characteristics of PD lack in-depth analysis of reaction mechanisms and spectral evolution across different discharge stages. In this study, spectral measurements were performed from corona to arc discharge, covering deep ultraviolet to near-infrared regions. Through spectral analysis and calculations, the investigation revealed spectral evolution and energy distribution characteristics during discharge process. An energy level transition diagram was then established to elucidate potential reaction mechanism. The study found that with increasing discharge severity, spectral lines from atomic ionization appeared before N 2 + spectral lines, though this did not lead to breakdown. During critical breakdown phases as well as at spark discharge events, atomic emission lines at wavelengths beyond 760 nm in the infrared region showed significant enhancement, particularly the O I line at 777 nm. These characteristic spectral signatures emerge as critical indicators of discharge severity and predicting breakdown. Upon breakdown, the spectral intensity of N 2 + first negative band at 391 nm exhibited a dramatic increase, indicating that direct molecular ionization of N 2 into N 2 + was the primary mechanism responsible for the breakdown process. Chemical detection of O 3 and NO showed good agreement with the spectral analysis results. Additionally, the rapid consumption of NO in early stages indicated the formation of oxidizing species stronger than O 3 . Based on these findings, the study characterized the stage-specific discharge products and their degradation mechanisms on insulation materials, leading to targeted maintenance strategies.