Failure Modes of Laminate Structures

Laminate structures composed of alternating thin layers of conductor and dielectric material are commonly used in energy storage and transmission components. The failure of the dielectric layers in regions of high field stress, with applied 60 Hz ac, de and impulse voltages, was studied. Several geometries were compared, including staggered and fiush edges. Electrical trees developed between the laminated dielectric layers. The visual characteristics and growth rates of the electrical trees under ac, de and impulse stresses were different. Partial discharge detection and analysis was used to measure the inception voltage and discharge activity at the conductor edge voids, to observe tree formation and growth, and to predict impending failure due to dielectric erosion. Electric field distributions were modeled and partial discharge inception levels were estimated from known void geometries. The staggered edge geometry appears to enhance the electric field stress at the recessed electrode.