OPTICAL MONITOR FOR CONTAMINATION ON HV INSULATOR SURFACES

Ellipsometry is used to monitor naturally deposited contamination film s on HV electrical power insulators that are used in overhead transmis sion lines and substations. Good correlation is found between the conv entional ESDD (equivalent salt deposit density) method of measuring co ntamination and an ellipsometrically determined optical thickness of t hat contamination. The technique relies completely on the state of pol arization of light reflected from the surface of a ZnSe witness piece which is placed on or close to the power insulator. Such a technique r esults in the thickness and refractive index of the deposited contamin ant. The severity of contamination is then known by the value of the m easured film thickness. Three patches of witness pieces were placed in the Labarre substation in New Orleans, LA. Comparison between convent ional ESDD and ellipsometric measurements showed good agreement.