Optical monitor for contamination on HV insulator surfaces

Ellipsometry is used to monitor naturally deposited contamination films on HV electrical power insulators that are used in overhead transmission lines and substations. Good correlation is found between the conventional ESDD (equivalent salt deposit density) method of measuring contamination and an ellipsometrically determined optical thickness of that contamination. The technique relies completely on the state of polarization of light reflected from the surface of a ZnSe witness piece which is placed on or close to the power insulator. Such a technique results in the thickness and refractive index of the deposited contaminant. The severity of contamination is then known by the value of the measured film thickness. Three patches of witness pieces were placed in the Labarre substation in New Orleans, LA. Comparison between conventional ESDD and ellipsometric measurements showed good agreement.