Recurrence plot analysis of discharge currents in tracking tests of gamma-ray irradiated polymers

Due to the widespread use of polymeric insulating materials in radiation environments, there is an increasing demand to evaluate the radiation effects on the surface dielectric characteristics of polymeric insulating materials. This paper presents a recurrence plot approach to analyze the surface discharge of gamma-ray irradiated polymeric insulating materials based on the tracking test described in IEC60112. Because the resulting comparative tracking index has wide variation, an attempt has been made to evaluate the resistance to tracking more consistently. In this research, for different dosages of gamma-ray irradiation, the discharge currents are detected when the discharge occurs on the sample surface. Recurrence plots of the discharge currents are derived. It is found that the resistance to tracking could be projected on a map as a function of the dosage of irradiation. The recurrence plots are sensitive and give visual methods for identification of the dosage of irradiation effects on the resistance to tracking. Results obtained show that with the increase of dosage of irradiation, the resistance to tracking of polybutylene terephthalate decreases, but increases for polyethylene terephthalate.