Allan T. Johns is Professor of Electrical Engineering and Head of the School of Electronic and Electrical Engineering at the University of Bath. He is the author of over 200 journal papers, and in 1982 he was awarded the degree of Doctor of Science for his original and substantial contribution to knowledge in the area of digital protection and simulation of electrical power systems. He worked for nine years in British industry, both in electricity supply and in manufacturing, and is still heavily involved in industrial consultancy. He is a Fellow of the IEE, a Series Editor for the IEE Power Series of books and Tutorial Editor of Power Engineering Journal. Among the awards he has earned are the IEE Crompton Premium in 1983 and the IEE Power Divisional Board Premium in 1989. Salman K. Salman is with the School of Electronic & Electrical Engineering at the Robert Gordon University in Aberdeen. His research interest covers analysis and protection of power systems. A graduate of Baghdad University, Sheffield University and UMIST, he is the author or co-author of more than 35 papers. He spent six years working in the electricity supply industry, and before his current position was Associate Professor at the Behghazi University, Libya. Dr. Salman is a Member of the IEE and a Senior member of the IEEE.