Theoretical model of applying radiometry to monitor insulator contamination

This paper introduces a novel method for monitoring contamination levels on high voltage insulators based on microwave radiometry. Contamination monitoring systems for high voltage insulators are often based on leakage current measurements using either a current transformer or a shunt resistor. These traditional systems suffer from two drawbacks: (1) they require physical installation onto the insulator circuit and (2) they are best suited to detecting contamination severity when the insulator surface is wet; a condition in which flashover is likely to occur within a short time period. The described microwave radiometer measures energy emitted from the contamination layer and could provide a safe, reliable, contactless monitoring method that is effective under dry conditions. This will potentially facilitate advanced warning of the future failure of a wet insulator in climates where insulators experience dry conditions for extended periods. The relationship between equivalent salt deposit density and radiometer output is presented using a dielectric mixing model and a brightness temperature model. A dielectric mixing model is presented to evaluate the dielectric properties of insulator contamination as a function of moisture, salinity, environment temperature and humidity. A brightness temperature model is also presented, which describes the influence of the dielectric properties on emissivity of the insulator contamination layer. This paper provides a basis for future work on the development of an on-line monitoring system.