Effect of discharges between electrodes on the surface of organic insulation

Measurements of the temperature of the surface of polymeric insulating materials immediately under discharges between electrodes upon the surface show that a `breakdown¿ temperature can be defined, which is constant for each material. It is shown that this temperature is related to thermal decomposition of the insulating material. For any particular geometry, a `threshold¿ current exists for each material, which can be predicted from a knowledge of the heat-conduction field in the material and the breakdown temperature. These results are useful in interpretation of tracking and erosion test results and for the design of insulators manufactured from synthetic resin.