This book provides a detailed overview of the vulnerabilities of digital protection relays to natural and intentional destructive impacts. From lightning strikes, electromagnetic fields generated by operating equipment, and issues with control cable shielding to modern technical tools that realize intentional destructive impacts remotely, this first-of-its-kind text covers the latest cyber and electromagnetic threats to digital protection relays. It discusses passive means of protection, such as screened cabinets, filters, cables, special materials, and covers, as well as advanced solutions based on hardware methods.