If the field strength between two electrodes caused by electric fields exceeds a certain value, charge equalization takes place between them. This is announced by ionization and results in an electric spark.
The charge balance and the associated field strength depend on the type and distance of the two conductors, which are conductive, pointed, flat or round electrodes. Charge equalization occurs sooner on pointed conductors because the field lines are concentrated at the tips. Likewise, the electric fields increase when the distance between the conductors is reduced.
Charge equalization can be prevented by non-conductive and insulating materials inserted between the two electrodes. With such insulating materials, it is possible to increase the field strength without charge equalization taking place. The property that characterizes such materials is their dielectric strength. Depending on the material, this ranges from 3.3 kV/mm for air and rises to 20 kV/mm for porcelain, 50 kV/mm for polyvinyl chloride( PVC), up to 100 kV/mm for polypropylene ( PP) and 10 kV/mm for polystyrene( PS).
Dielectric strength is important wherever higher voltages are transformed and transmitted. Intransformers, capacitors, surge arresters, high- voltage lines, etc.