Effect of voltage frequency on surface discharge characteristics and aging process

Power electronic transformers, also known as solid state transformers, are drawing more and more attention of the researchers. One of its key components is high frequency power transformer (HFPT) subjected to electrical stress of several kilohertz. Voltage frequency has a significant impact on discharge behaviors of insulation material, or even brings about accelerated insulation aging and premature failure. In order to investigate the influence of voltage frequency on surface discharge behaviors and aging process, an experimental platform with variable applied voltage for electrical aging tests was set up. Presented aging tests in this paper were conducted on polyimide films subjected to surface discharges under sinusoidal voltage at different frequencies ranging from 5 kHz to 30 kHz. In the paper special focus is given to the lifetime of specimens and discharge characteristics, including maximum and average discharge amplitude, total discharge number and amplitude per cycle or per second. In terms of these data, insulation lifetime plot relevant to voltage frequency is computed, and the correlation between lifetime and discharge characteristics is built, considering partial discharge as the core cause of insulation failure. Experimental results reveal the accelerated aging mechanism from high frequency electrical stresses based on the analyses of lifetime and discharge characteristics of specimens under different frequencies.