High quality electrical service is key to power systems around the world, particularly in utilities and industrial facilities. Both voltage and grid frequency must be kept within tight limits to maintain functioning of critical infrastructure. The growing use of renewable power of intermittent character is adding to that challenge. One of the keys to achieving quality service is the protection system, which needs to be reliable, fast and with a good cost/benefit ratio. It consists of various components, including relays, circuit breakers and fuses. An understanding of the different behaviours of these components in the face of malfunctions, and of countermeasures, is needed. This book has established itself as a classic work in its field, allowing the reader to easily follow the ideas explored. It provides an overview of most aspects of electrical protections, with emphasis on distribution systems; but protection of generation and transmission systems are also addressed. For this 4th edition, new topics have been added, such as protection of renewable power plants and transient stability analysis. It offers a thorough revision of the material, particularly the numerical type of relays, protective functions, control, measurement, communications and oscillography features. Most chapters have illustrative examples using MATLAB or PSAT (Power System Analysis Tools). This work remains essential reading for researchers, utility engineers, design, maintenance and consulting engineers as well as for instructors and senior students.