Effects of thickness and area on the electric strength of polymers

When the short-time electric strength (E/sub st/) of low loss polymers is determined in accordance with IEC 243, breakdown is usually caused by 'surface discharges'. Unless there are gross isolated defects, E/sub st/ is more dependent on the thickness d than on the area of the samples. E/sub st/ is affected by the permittivity and electric strength of the immersion medium and when d>0.1 mm, E/sub st/ is usually higher when samples are tested in air than in a clean transformer oil.>