Surface contamination of insulators in high voltage transmission and distribution systems may lead to troublesome flashovers which interrupt service. Insulator contamination may be monitored using direct measurement of equivalent salt deposit density (ESDD), which directly relates to the flashover voltage. A fiber-optic evanescent- coupling fiber-optic ESDD monitor is presented. The use of a piece of D-shape E-core fiber as sensor head can provide a sensitive and large area ESDD monitoring system. We have demonstrated the use of D-shape fiber in monitoring ESDD on insulator surfaces. A simple process has been developed to precisely etch the D-fiber. The polarimetric and evanescent loss sensors have been investigated. The evanescent loss sensor is particularly suitable for in-situ ESDD monitoring in power transmission lines and substations.
A division-of-aperture in-line fiber-optic photopolarimeter using a 1 by 5 fused fiberoptic star coupler has been demonstrated. All five output beams of the star coupler have nearly identical states of polarization except that they have unknown orientations of optical axes. The photopolarimeter output is taken from one of the star coupler output beams, whose state of polarization is measured from the other four beams. The construction of the in-line photopolarimeter is identical to that of conventional ones except that the linear and circular analyzers are aligned with the respective beam optical axes determined from calibration. Such a system is compact, light weight, efficient, robust and inexpensive. The new photopolarimeter agrees within one percent with a HP 8509A off-line photopolarimeter.