Monitoring contamination level on insulator materials under dry condition with a microwave reflectometer

Current techniques used for monitoring the levels of contamination on high voltage insulators, such as leakage current and infrared, are not effective in dry conditions since they require the surface of the insulator to be wetted by fog, rain or snow. If a buildup of contamination occurs during a prolonged dry period prior to a weather change there will be a significant risk that flashover may occur before there is time to implement preventative maintenance. Previous work has demonstrated the use of microwave radiometry to determine the levels of contamination on an insulator material under dry conditions, however practical applications are limited by low sensitivity. This paper reports the development of a novel technique based on microwave reflectometry to detect the power levels reflected from the surface of the insulator material. The level of contamination is then determined as a function of received power. A theoretical model establishes the relationship between equivalent salt deposit density levels on insulator surface and the dielectric properties of the contamination layer. A Finite Difference Time Domain (FDTD) model is used to simulate the total loss as a function of the contamination level. Experimental results verify the FDTD model and demonstrate the sensitivity of the reflectometer system to be approximately 100 times greater than the radiometer system. Therefore, the reflectometry system has considerably greater potential for practical applications to provide advance warning of the future failure of insulators under dry conditions for both HVDC and HVAC systems

Feasibility study on application of microwave radiometry to monitor contamination level on insulator materials

This paper introduces a novel method for monitoring contamination levels on high voltage insulators based on microwave radiometry. Present contamination monitoring solutions for high voltage insulators are only effective in predicting flashover risk when the contamination layer has been wetted by rain, fog or condensation. The challenge comes where the pollution occurs during a dry period prior to a weather change. Under these conditions, flashover can often occur within a short time period after wetting and is not predicted by measurements taken in the dry period. The microwave radiometer system described in this paper measures energy emitted from the contamination layer and could provide a safe, reliable, contactless monitoring method that is effective under dry conditions. The relationship between equivalent salt deposit density and radiometer output is described using a theoretical model and experimentally verified using a specially designed X-band radiometer. Results demonstrate that the output from the radiometer is able to clearly distinguish between different levels of contamination on insulator materials under dry conditions. This novel contamination monitoring method could potentially provide advance warning of the future failure of wet insulators in climates where insulators can experience dry conditions for extended periods