Measurements of temperature dependence of partial discharge in air gaps between insulated Bi-Sr-Ca-Cu-O tapes

Partial discharge (PD) in trapped air-filled gaps between two adjacent insulated high temperature superconducting (HTS) tapes made of Bi₂Sr₂Ca₂Cu₃O_x (BSCCO) was investigated experimentally. PD measurements were performed at several temperatures ranging from 295 K to 41 K. At each temperature a series of AC voltages of equal duration and increasing magnitude was applied to the inter-turn insulation until PD was initiated and observed on the insulation condition monitor ICM digital PD system. The PD data are presented in the form of phase and amplitude resolved PD (PRPD) patterns. The voltage at which PD initiation (PDIV) and extinction (PVEV) is observed at a particular temperature was measured on an oscilloscope. Experimentally obtained PDIV and PDEV values are compared with the Paschen curve values for air and the effect of temperature on PDIV is discussed. The data show that relatively low PD onsets can occur even when the insulation is cooled to the 40 to 50 K range which may be due to the presence of ice layers on the surface of the voids.