Effects of Antioxidant Additives on Electrical Tree Characteristics in EPDM Under Liquid Nitrogen

To investigate liquid nitrogen (LN
₂
) effects on insulation materials in high temperature superconducting (HTS) systems, the electrical tree was studied in ethylene propylene diene monomer (EPDM)/antioxidant specimens by using a needle-plane electrode system. The pulse amplitude and frequency were 25 kV and 200 Hz, respectively. In LN
₂
, as the free volume was reduced and the nonband energy got larger, the charge carriers were difficult to migrate in the samples. The charge trapping center was decreased from 0.925 to 0.195 eV as the temperature was reduced from 293 to 77 K, there were less charges to collide with molecular chains in LN
₂
. The electrical tree growth was restrained in EPDM specimens under LN
₂
. When the antioxidant was filled into EPDM, the charge trapping center was increased from 0.195 to 0.21 eV, the nonband energy was improved to reach a more stable state. Thus, the antioxidant could be served as the degradation inhibitor in EPDM/antioxidant specimens by regulating the charge transportation to restrain the electrical treeing process. This research has substantial commercial significance for insulation design and preshipment inspections in HTS insulation areas.