Protective relays and devices have been developed over 100 years ago to provide “last line” of defense for the electrical systems. They are intended to quickly identify a fault and isolate it so the balance of the system continue to run under normal conditions. What controls it: Relay performance depends on the protected zone, CT/PT inputs, pickup settings, time delay, breaker clearing time, trip. An electrically operated switch like a relay plays a key role in controlling an electrical circuit through an independent low-power signal, otherwise used where a number of circuits should be controlled through the single signal. Types of Protective Relays: Protective relays are categorized by their mechanism (electromagnetic, static, mechanical) and function. Static Relays: Use solid-state electronic components to process analog input signals without moving parts, providing faster response and greater reliability. Digital/Numerical Relays: Employ microprocessors and software algorithms to analyze electrical quantities, execute multiple protection. Protective relays can be classified based on their operating principle, construction, or function: 1. Based on Operating Principle Electromechanical Relays: Work using moving parts and electromagnetic forces (traditional relays).
