High Temperature Insulation Materials for DC Cable Insulation — Part I: Space Charge and Conduction

Fundamental studies of potential candidates for DC electric power transmission in high temperature environment, including ETFE, FEP, PTFE, PI and PEEK, are carried out and presented in form of the series papers containing space charge and conduction as part I, partial discharge as part II, and the degradation and surface breakdown as part III. In this part, the space charge at 20kV/mm was measured at 25 °C and with a thermal gradient at 50 °C. The electrical conductivity was measured at electric fields ranging from 10kV/mm to 30kV/mm in temperatures ranging from 25 °C to 200 °C. The experimental results showed that considering the effect of thermal condition and electric field, FEP has the lowest total amount of space charge accumulation and electric field distortion among these materials at the measured conditions. PI and PEEK have the lowest amount of trap-controlled mobility at 25 °C due to deeper average trap level because of the aromatic rings in the structure. PTFE and PI have the lowest amount of thermal activation energy and temperature-dependent electrical conductivity due to the more uniform morphological phase comparing to ETFE, FEP, and PEEK. The outcomes of this paper serve as a benchmark for the fundamental researches over high temperature materials for DC applications and lay a basis for Part II and Part III.