Discharge phenomena in voids filled with fibrous materials

To obtain a waterstop in the longitudinal direction of a three-phase belted cable, a thin nonwoven tape was applied to the core insulation and to the interstices between the belt insulation and the core insulation. As these tapes are very poor dielectrics with low breakdown stress, it was expected that the breakdown tests would be impaired. On the contrary, the life expectancy was raised from less than 10 years to more than 30 years at 10 kV. Further study revealed that this dielectric improvement was caused by a considerable reduction of the discharges in the interstices of the cable; reductions of several hundred times were measured. The fibers at the air-dielectric interface appear to act as barriers for the surface discharges