الفهرس 
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Abstract
The flashover of polluted voltage insulators is one of the major problems for operation of transmission lines and substations in Egypt. In January 2010, the insulators’ pollution was the cause of several interruptions in the Egyptian electrical network. The insulator begins to fail when the pollutants which exist in the air settle on the surface of the insulator forming an electrolyte layer on the insulator surface under the influence of environment and weather conditions such as humidity, fog, rain, or dew. The significant variation of the climatic conditions and the large industrial developments in the last few years necessitated to update the map of the distribution of pollution especially in northern Egypt (Cairo and Alexandria) and asses the outdoor insulator behavior in these regions. To achieve this, six sites in both cities of different types of pollutions have been investigated. These sites cover marine pollution, Light mixture between marine, Desert and Industrial (cement), carbon pollution (Brick Kilns), mixture between marine pollution and industrial pollution (iron), mixture between quarries pollution and desert pollution, and finally mixture between desert pollution and industrial pollution (cement). In order to assess the behaviour of line insulators in these sites, IEC standard cap-pin suspension insulators were hanged for a time zone of 5 months and study the effect of pollution upon the performance of insulators through the measurement of; equivalent salt deposition density (ESDD), surface conductivity (SC), maximum leakage current (MLC) and flashover voltage (FOV) were carried out. The naturally polluted insulators have been tested in the Pyramids High Voltage Research Center (PHVRC), Cairo, Egypt. Also, to quantify the contaminants on outdoor insulators, numerous samples are gathered from these regions and subjected to a comprehensive chemical analysis at the scale analysis laboratory of the Egyptian Electricity xi Transmission Company. Regression models for predicting the flashover voltage as related to ESDD and MLC as related to surface conductivity were developed. The models were validated through statistical analysis as well as comparison with measured data. The obtained results would be useful: to assess the insulation performance in different environmental situations and to improve the design if necessary, to determine the rate of contamination in various environments, to decide the periodical maintenance and suitable method of maintenance, to suggest the proper creepage distance of insulator and finally propose an updated pollution map in northern Egypt.