A relay protection system is a comprehensive network of protective relays and associated devices designed to detect and isolate faults within a power system. Its primary purpose is to maintain the integrity of the grid by minimizing the impact of a fault, ensuring safety, and preventing damage to expensive equipment like transformers and generators. The system's operation is based on the principle of selectivity, where only the faulty section of the grid is isolated while the rest of the system remains operational, thereby ensuring a continuous power supply.

A typical relay protection system is composed of various types of relays, each with a specific function. For instance, overcurrent relays protect against current overloads, while distance protection relays are used for long transmission lines. The system also includes circuit breakers, which are the devices that physically interrupt the current flow, and current and voltage transformers that provide the necessary inputs to the relays. With the advent of digital protective relays, these systems have become more intelligent and integrated. Modern systems can communicate with each other, share data, and coordinate their actions to provide a faster and more precise response to a fault. The shift toward a smarter, more resilient grid is making the design and implementation of sophisticated relay protection systems more critical than ever before.