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. 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. In order to further improve the operational reliability of high-voltage relay protection equipment and reduce equipment maintenance costs, a comprehensive judgment method for the operation status of high-voltage relay protection equipment based on association rules and cloud model was proposed. By. This handbook covers the code of practice in protection circuitry including standard lead and device numbers, mode of connections at terminal strips, colour codes in multicore cables, dos and donts in execution. 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 order to verify the proper operation of complex multifunctional microprocessor-based protection devices (MPD) at their inspection, start-up after repairs, or during periodic tests, they should be tested for proper operation at several of the most critical preset characteristic points as well as.