Identification of Insulation Defects in Cryogenic Dielectric Materials for the HTS Power Applications

Recently, various high temperature superconducting (HTS) power applications have been developed and prepared for field tests and commercial applications. Comparing to conventional power applications, it could offer several advantages such as reduced size and weight, high efficiency, decreased losses, no oil, nonflammable and decrease of CO2 emissions. Besides overload operation is possible with no loss of lifetime. For HTS power applications in low temperature and high voltage environments, partial discharge (PD) measurements in cryogenic dielectric materials of HTS power applications are very important because PD was regarded as primary source for ageing and breakdown of cryogenic materials. One of the diagnostic methods for safety of the power components, the detection of PD taking place inside the apparatus has been widely investigated. The first method, phase resolved partial discharge (PRPD) Analysis was developed in the early 1970s taking the phase information of the applied AC voltage into account. We also proposed a pattern analysis method named chaotic analysis of PD(CAPD) for PDs occurred in liquid nitrogen, considering three normalized parameters obtained from the values between two consecutive PD pulses: amplitude difference (P_t), occurring time difference (T_t) and correlation between T_t and P_t. This pattern analysis method can identify the type of defects by means of PD pattern classification without employing the phase information of the applied voltage signal. For the experimental investigation, three artificial defects have been fabricated considering possible defects formed during the manufacturing process of HTS power applications: turn to turn insulation, floating particle and protrusion. And PD signals originated from these artificial defects are measured and analyzed by means of CAPD. Throughout this work, it seems that the correlation between the consecutive PD pulses, depending on the nature PDs, co- ld be clarified by CAPD.