Fractal analysis of discharge current on polybutylene terephthalate

In this paper, an artificial atmospheric chamber was set up to investigate the fractal characteristic of discharge currents on polybutylene terephthalate under a reduced pressure. The decompression chamber was made from a glass cylinder with two sheets of acrylic board for the cover and the bottom. The test equipment was placed in the chamber, and the pressure was reduced from 100 kPa to 1 kPa by using a rotary pump. The experiment was carried out on the sample surface by a DC pulse voltage applied between a plate electrode and a needle electrode. The distance between the two electrodes was 6 mm. The frequency of applied pulse voltage ranged from 100 Hz to 250 Hz. The effects of atmospheric pressure and the frequency of applied voltage on the discharge currents have been studied. The fractal theory is used to analyze the discharge characteristics. The fractal dimension of discharge currents increases inversely with decreasing the atmospheric pressure and decreases with increasing the frequency of applied voltage. It is suggested that the fractal dimension can be used to analyze the insulation degradation of polybutylene terephthalate