Influence of aged conductor surface conditions on AC corona discharge with a corona cage

Relatively little investigation has previously been done on the effects of aging on conductor surface conditions, or on the ac corona discharges from these conductors. In the present work these were investigated by means of comparing corona on typical aged conductors with that on new ones. The aged conductors from the ac power transmission lines had been in service for 12, 15 and 20 years. Scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis were employed to characterize the surface morphology and composition of the conductors; and a non-contact surface profiler was used to measure the surface roughness of the six samples. As a result of corrosion and the adherence of various substances to the conductors, their surfaces were far rougher than the new ones. The ac corona discharge characteristics of these conductors were studied in a small corona cage using an ultraviolet imaging detector. As a result of the rough surfaces, the corona discharge intensity for the aged conductors was found to be much stronger than that for the new ones; and the corona inception voltages for the aged conductors were 10 to 25% lower than the new ones.