This book is a long awaited comprehensive introduction to the protection of electrical power systems using computer-based methods (i.e. digital relays). The treatment is logically structured, taking the reader through the mathematics and principles underlying the development and implementation of the major algorithms underlying different protection techniques. They can be applied to protection of generator transformers, lines, switchgear and cable the main components of transmission and distribution systems. The book deals with the research and development activity in the field of digital protection during the last 15 years. The reader will become familiarised with the fast developing field of power system protection using computers and microcomputers. This book provides a full introduction for senior undergraduates and graduates, and acts as a sound reference for engineers already practising in this area.