Surface electrical failure in the presence of contaminants: The inclined-plane liquid-contaminant test

Electrical failure of the surface of insulating materials can occur in several ways. These include: 1. Air breakdown (flashover) which transfers to the adjacent insulation surface. 2. Thermal degradation of the surface (from arc interruption nearby, etc.) which temporarily or permanently damages the surface so that electrical failure occurs. 3. Partial volume breakdown, particularly of alminates, just beneath the surface which produces thermal or other degradation so that final failure ultimately occurs on the surface. 4. Surface degradation from electrical corona starting initially in limited surface areas exposed to voltage gradients high enough to produce localized air breakdown. 5. Progressive failure across the surface resulting from tiny arcs (scintillation) caused by conducting, or partially conducting, surface contamination.