Longfei Cui

Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Electrical and Computer Engineering

Committee Chair

Ravi Gorur

Committee Member

Shangbing Ai

Committee Member

David Pan

Committee Member

Maria Pour

Committee Member

Yuri Shtessel


Electric insulators and insulation, Dielectrics, Electric power transmission


The economy of transporting large amount of power over long distance makes high voltage transmission line an important component of the power system. The continuous and stable operation of the transmission lines are critical for the power system. Outdoor insulators provide electrical insulation as well as mechanical support between energized conductor and grounded parts. Therefore, insulator performance is intimately related to the reliability of power delivery. Insulator performance is affected by weather parameters (such as rain and pollution) and aging characteristics of its components. High voltage transmission lines, passing through high vegetation areas, also face a risk of wildfire. During fire fighting activities, large amount of fire retardant is used to extinguish the fire. Under such severe and complex operation environment, there is pressing demand for utilities to obtain a simplified and rapid insulator diagnosis method to schedule an overhaul or replacement of aging insulators, so as to ensure operational continuity and reduce economic losses. In order to explore the characteristics of insulator flashover, experiments were conducted to gather flashover data for both composite and ceramic insulators, varying from distribution to transmission classes. Conventional pollutant and a new type of pollutant, a commercial fire retardant, were studied to learn their effect on the surface condition of insulators. A regression model was built to predict insulators’ performance under fire retardant conditions for higher voltage levels. Recommendations for insulator design have been provided for transmission lines located in the forest areas. A generalized statistical model was developed to predict flashover probability with a wide range of pollution severities, insulator shapes and materials. The model was validated with sensitivity analysis. Collecting all those parameters would be complex and challenging implement for utilities’ in-service insulator inspection. Insulator performance is most sensitive to electric field distribution inside and surrounding the insulator. Accordingly, a novel electric field measurement technology, which was commercially available recently, was utilized in the research to measure the electric field distribution around the insulators. The patterns of the electric field distribution were studied and its relation with the flashover voltages was explored. Further, electric field calculation with the boundary element method (BEM) was performed to validate the experiment results and broaden the conclusion to higher voltage levels.



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