This presentation reviews the established principles and the advanced aspects of the selection and application of protective relays in the overall protection system, multifunctional numerical devices application for power distribution and industrial systems, and addresses some. This presentation reviews the established principles and the advanced aspects of the selection and application of protective relays in the overall protection system, multifunctional numerical devices application for power distribution and industrial systems, and addresses some. Protective relays are essential devices used in electrical power systems to detect faults and abnormal conditions, initiating corrective actions to prevent equipment damage and ensure system stability. These relays play a crucial role in the protection of transformers, generators, transmission. 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. The selection and applications of. In modern industrial plant maintenance, protective relays play a critical role in preventing equipment damage, minimizing downtime, and ensuring worker safety.