Research the length of the positive corona using the digital image processing technology

This paper presents an experimental study of dc air discharge in a point-line electrode system. The digital image processing technology presented in our previously paper is used to calculate the length of the positive corona. The calculated results of the mean gray level, the standard deviation of the gray levels and the coefficient of variation which is the ratio of the standard deviation to the mean gray level, show that the jump location of the coefficient of variation is the end point of the corona and can be used as an index of the length of corona. With an increase of the voltage, the length of corona increases and the positive corona mingles with the negative corona at last. Compared with the other methods, the method is not only effective but also simple in the quantitative analysis the length of the corona.