A test method using to measure the corona onset and the corona loss of transmission-line in a corona test cage is described. Compared the corona loss and the change of capacitance with the observation through a micro-light device

we found that there are different physical characteristics between rough factor and nature factor during the line corona. It is experimentally shown that the traditional method to measure the corona onset is obtained from mat hematic statistics

but the corona and its onset resulting from the nature factor this paper mentioned will be of greater value both in theory and in practice.