The Effect of Barriers in the Low Field Regions of Non-Uniform Fields on Oil Breakdown

The influence of barriers in mineral oil on the stress at which partial discharges initiate and also on the stress at which failure occurs was investigated for non-uniform fields. The failure stresses were found to depend on the location of the barrier, while the partial discharge onset stresses were independent of the location of the barrier in the low field region. The variation of the failure stresses was interpreted in terms of an assumed critical stress at the tip of the streamer that is required to puncture the barrier. The partial discharge onset behavior was shown to be consistent with a particle initiated breakdown in which a particle shape effect was introduced. In addition, the voltage endurance data were obtained for oil without barriers where the failure times ranged from a few cycles to hundreds of hours of 60 Hz.