LOW-TEMPERATURE DIELECTRIC LOSS DUE TO ANTIOXIDANTS IN POLYETHYLENE

Certain antioxidants added to polyethylene are known to cause increased dielectric loss in the audio-frequency range at liquid helium temperature. Although the peak loss factor occurs at several kilohertz, the increase at power transmission frequency is sufficient to affect the performance of an ac superconducting cable insulated with polyethylene tape. Contrary to recent reports, we now have reason to believe that the effect is an exclusive feature of antioxidant molecules which are 3, 5-ditert-butyl-4-hydroxy-phenyl compounds. It is attributable to tunnelling of the hydroxy hydrogen atom. Other substituted phenols and non-phenol antioxidants can all effectively protect the polyethylene without increasing the dielectric loss. 4.2 K dielectric loss measurement may be used as a rapid, sensitive and specific test for the presence of 3, 5-ditert-butyl-4-hydroxy-phenyl compounds in polyethylene. © 1979.