Probes for spot measurement of surface conductivity on polluted insulators

The surface conductivity of insulators in the field is often non-uniformly distributed. In this case the integral surface conductivity is not an appropriate parameter of pollution severity. A better evaluation can be achieved on the basis of local conductivity measurements by means of special probes, for example, the rod probe or tissue strip probe. In this work the form factors of different probes are given and the form factor for the rod probe was calculated. The influence of wet-contamination area, the meniscus and the pollution layer thickness on the measured value of surface conductivity are shown. It was found that the surface conductivity on polluted silicone rubber measured by a tissue strip probe is proportional to the equivalent contamination deposit density (ECDD).