In this book, most fundamental dimensional analysis technique is used to develop some mathematical relationships to understand the flashover mechanism of contaminated insulator. All mathematical models have been verified by the experiments. This book has been written based on PhD thesis. In addition, the relationships between leakage resistance and ESDD, and ESDD and wind velocity have been developed. The expression of time to flashover, flashover voltage in terms of ESDD and surface conductivity has been developed.